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Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
What I meant to write was: Like the transconductance values, the voltage across each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
The cathode resistors are new 15R, 1%, 1W.
Barry - N4BUQ
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Can someone please tell me what is meant by the term "soft finals"? I'm still
having problems getting proper output from my TR-4 and, for all I know, that
might be the problem. I've tested them for transconductance and all three are
very close to the same value and, furthermore, that value is quite a bit above
the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy
load), I notice that if I hold down the key for a few seconds the plate current
tends to drop just slightly and I think if I were to continue holding the key
down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same
phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit.
Like the transconductance values, each cathode resistor is "matched" in value
and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that
would cause this?
Thanks,
Barry - N4BUQ
|
"Soft" referring to a tube means gassy.? There are many symptoms of gas but a change in characteristics as the tube heads is one of them. Very gassy tubes can have a glow inside something like the glow in a voltage regulator tube ? However, tubes running at high voltage can have a slight glow without gas, and the glow on the inside surface of the glass envelope from high voltage is due to electron bombardment and is normal.
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Show quoted text
-------- Original message -------- From: n4buq <n4buq@...> Date: 5/17/25 8:44 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
What I meant to write was:? Like the transconductance values, the voltage across each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing. The cathode resistors are new 15R, 1%, 1W. Barry - N4BUQ > Can someone please tell me what is meant by the term "soft finals"?? I'm still > having problems getting proper output from my TR-4 and, for all I know, that > might be the problem.? I've tested them for transconductance and all three are > very close to the same value and, furthermore, that value is quite a bit above > the minimum for a good tube. > > Aside from low output (i.e. about 300 mA plate current maximum into a dummy > load), I notice that if I hold down the key for a few seconds the plate current > tends to drop just slightly and I think if I were to continue holding the key > down, the current would continue to slowly decrease. > > I measured the voltage across each cathode resistor and I notice the same > phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. > Like the transconductance values, each cathode resistor is "matched" in value > and behavior to the other two so I suppose that's one good thing. > > Am I seeing the result of weak/soft tubes or is something else going on that > would cause this? > > Thanks, > Barry - N4BUQ > > >
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Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq < n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Richard, Steve,
Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing.
Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
There is a common misconception that our Drake rigs were designed for 115VAC or even 110VAC.? They were designed for 120VAC nominal -- which, through all my years of testing and helping to design raw and linear power supplies, were given a tolerance of +/-5% (so, 114 - 126 VAC.? Of course many of those supplies would do just fine outside that tolerance band.? It also explains why you get 6.3VAC at the filaments at 120VAC.
When I started working as a tech in 1976, 120VAC had already been the standard.? Interestingly, the buss bars at out plant were sometimes labelled "120V/60CPS", so the changeover to 120 preceded the changeover from CPS to Hz.
We had the whole gamut in that Digital Equipment plant: 120/240 single-phase and 208/440 three-phase (IIRC).? Our equipment runs fine at 120VAC.? Yes, you can eke a little more tube life running the filaments slightly lower but our rigs were designed for 120 (it's in the manuals).
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Sunday, May 18th, 2025 at 6:23 PM, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
I found a couple of references that agree that the standard US line voltage went to 120 in 1967.
The US started at 110/220 in the late 1800s because Edison¡¯s light bulbs were designed for 110 ¡ª AC or DC.
Europe started well after the US, in Germany, and started with 220V, 50 Hz. ?The rest of Europe and colonies followed.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, May 18, 2025 at 6:35 PM, Steve Wedge, W1ES/4 via groups.io < w1es@...> wrote:
There is a common misconception that our Drake rigs were designed for 115VAC or even 110VAC.? They were designed for 120VAC nominal -- which, through all my years of testing and helping to design raw and linear power supplies, were given a tolerance of +/-5% (so, 114 - 126 VAC.? Of course many of those supplies would do just fine outside that tolerance band.? It also explains why you get 6.3VAC at the filaments at 120VAC.
When I started working as a tech in 1976, 120VAC had already been the standard.? Interestingly, the buss bars at out plant were sometimes labelled "120V/60CPS", so the changeover to 120 preceded the changeover from CPS to Hz.
We had the whole gamut in that Digital Equipment plant: 120/240 single-phase and 208/440 three-phase (IIRC).? Our equipment runs fine at 120VAC.? Yes, you can eke a little more tube life running the filaments slightly lower but our rigs were designed for 120 (it's in the manuals).
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with
secure email.
On Sunday, May 18th, 2025 at 6:23 PM, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks,
Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve,
Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing.
Thanks again,
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <
n4buq@...> wrote:
Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Out mains typically runs 126VAC and that puts the HV well over 700VDC (I don't recall the exact value at the moment).? 6JB6s are rated at 770VDC plate voltage max so I think that's probably okay.
I bought a heavy-duty transformer with two 12VAC windings that, when in parallel, can give 8A that I want to use as a bucker.? In retrospect, that may not work as well as I'd hoped and I may need to look for a 6VAC version.? If the the rig is intended to run with the AC-4 at 120VAC, then perhaps that extra 6V may not matter too much and I can just leave the bucker out of the setup.? I was just looking at prolonging the life of the tubes as much as practical.
Thanks for the info.? I was thinking that 115 was probably the standard when these rigs were built but apparently that's not the case.
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 5:35:37 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
There is a common misconception that our Drake rigs were designed for 115VAC or even 110VAC.? They were designed for 120VAC nominal -- which, through all my years of testing and helping to design raw and linear power supplies, were given a tolerance of +/-5% (so, 114 - 126 VAC.? Of course many of those supplies would do just fine outside that tolerance band.? It also explains why you get 6.3VAC at the filaments at 120VAC.
When I started working as a tech in 1976, 120VAC had already been the standard.? Interestingly, the buss bars at out plant were sometimes labelled "120V/60CPS", so the changeover to 120 preceded the changeover from CPS to Hz.
We had the whole gamut in that Digital Equipment plant: 120/240 single-phase and 208/440 three-phase (IIRC).? Our equipment runs fine at 120VAC.? Yes, you can eke a little more tube life running the filaments slightly lower but our rigs were designed for 120 (it's in the manuals).
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Sunday, May 18th, 2025 at 6:23 PM, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down. With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess. Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage. Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Barry, Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73, Another Barry KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
I have found that virtually all of the resistors in my TR-4 have not aged out of tolerance which is a little surprising.? ?I did, though, replace the three 15R cathode resistors.? I think one or two were over 20 ohms but I replaced them mainly because they were no longer all the same value.
Since R13 is "selected", then I presume one can read the bands and should be able to check whether it's out of tolerance.? At least R45 is not "selected".
Thanks for the tip! Barry - N4BUQ (the other, other Barry)
Barry, Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73, Another Barry KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Make that "R13A is selected".? I was looking at the schematic for my version (schematic 26000) and that resistor was still labeled simply R13, which was already taken by the "real" R13 at V3.
Thanks, Barry - N4BUQ
I have found that virtually all of the resistors in my TR-4 have not aged out of tolerance which is a little surprising.? ?I did, though, replace the three 15R cathode resistors.? I think one or two were over 20 ohms but I replaced them mainly because they were no longer all the same value. Since R13 is "selected", then I presume one can read the bands and should be able to check whether it's out of tolerance.? At least R45 is not "selected". Thanks for the tip! Barry - N4BUQ (the other, other Barry)
Barry, Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73, Another Barry KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Interesting topic about the aging resistors in our 4-line gear.
Any time a rig comes into the shop ALL resistors get visibly?checked, but some get more attention than others.....
Here they are...
All PA screen and cathode resistors on the T-4X(any) and TR-4(any), as we all know.
On the T4XC...R-81 and R91 in plate leads to V-9.? Both are high value resistors which tend to go high with time, reducing plate voltage.? If your audio drive seems low check?these for sure. Also check Plate Voltage on V-9, and if below spec, these resistors are likely the reason.? I found plate voltage on one T-4XC I fixed for a friend years ago at +69VDC on V-9, while spec is +95VDC.? R81 had?gone way?high. Drakes aren't the only rigs I see this?happening to.? K4OAH's "CD's" will help you locate the?resistors, though that's just the start of the fun!? Frankly, ALL resistors with values above?200K or so deserve a resistance?check.? Doesn't seem to be as big an issue on the B-line and?earlier?in this circuit as the circuits are different and resistances are lower....cursory check though, so keep that in mind.
Also on the T-4XC...R49 and R59 on the relay board.? Often seen heat-stressed.
On the TR-4C series...R 192 and R-45 on the relay board.
On all TR-4(any) - R163 on the 200 VDC line to the S meter.? ?It seems to act as a fuse and have found several visibly?open!!!
I'm sure there are more, but this is a start.? I'm sure there are others who can add to the list.
73 Peter VE7PS
I have found that virtually all of the resistors in my TR-4 have not aged out of tolerance which is a little surprising.? ?I did, though, replace the three 15R cathode resistors.? I think one or two were over 20 ohms but I replaced them mainly because they were no longer all the same value.
Since R13 is "selected", then I presume one can read the bands and should be able to check whether it's out of tolerance.? At least R45 is not "selected".
Thanks for the tip! Barry - N4BUQ (the other, other Barry)
Barry, Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73, Another Barry KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq < n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks, Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve, Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true. My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing. Thanks again, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via " <w1es=[email protected]>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example.? Power falls off first on the higherbands as the gain (transconductance) decreases.? The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load.? The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <n4buq@...> wrote: Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Speaking of resistors, Where are you sourcing your resistors??
?
Thanks
?
George NE2I
|
My mains can get to 126, so I set my variac to around 118. It doesn¡¯t hurt. All modern equipment that aren¡¯t controlled by the C-4 runs on the mains directly.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, May 18, 2025 at 20:05, n4buq < n4buq@...> wrote:
Out mains typically runs 126VAC and that puts the HV well over 700VDC (I don't recall the exact value at the moment).? 6JB6s are rated at 770VDC plate voltage max so I think that's probably okay.
I bought a heavy-duty transformer with two 12VAC windings that, when in parallel, can give 8A that I want to use as a bucker.? In retrospect, that may not work as well as I'd hoped and I may need to look for a 6VAC version.? If the the rig is intended to run with the AC-4 at 120VAC, then perhaps that extra 6V may not matter too much and I can just leave the bucker out of the setup.? I was just looking at prolonging the life of the tubes as much as practical.
Thanks for the info.? I was thinking that 115 was probably the standard when these rigs were built but apparently that's not the case.
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 5:35:37 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
There is a common misconception that our Drake rigs were designed for 115VAC or even 110VAC.? They were designed for 120VAC nominal -- which, through all my years of testing and helping to design raw and linear power supplies, were given a tolerance of +/-5% (so, 114 - 126 VAC.? Of course many of those supplies would do just fine outside that tolerance band.? It also explains why you get 6.3VAC at the filaments at 120VAC.
When I started working as a tech in 1976, 120VAC had already been the standard.? Interestingly, the buss bars at out plant were sometimes labelled "120V/60CPS", so the changeover to 120 preceded the changeover from CPS to Hz.
We had the whole gamut in that Digital Equipment plant: 120/240 single-phase and 208/440 three-phase (IIRC).? Our equipment runs fine at 120VAC.? Yes, you can eke a little more tube life running the filaments slightly lower but our rigs were designed for 120 (it's in the manuals).
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with
secure email.
On Sunday, May 18th, 2025 at 6:23 PM, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks,
Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve,
Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing.
Thanks again,
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <
n4buq@...> wrote:
Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
Of course, there¡¯s nothing to prevent any of us from replacing the SAT resistor with a pot and then being able to directly calibrate the metering during an alignment. I¡¯ve not done this but it¡¯s certainly doable ¡ª I just don¡¯t think that amount of precision buys much.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, May 18, 2025 at 21:49, n4buq < n4buq@...> wrote:
I have found that virtually all of the resistors in my TR-4 have not aged out of tolerance which is a little surprising.? ?I did, though, replace the three 15R cathode resistors.? I think one or two were over 20 ohms but I replaced them mainly because they were no longer all the same value.
Since R13 is "selected", then I presume one can read the bands and should be able to check whether it's out of tolerance.? At least R45 is not "selected".
Thanks for the tip!
Barry - N4BUQ (the other, other Barry)
Barry,
Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73,
Another Barry
KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks,
Barry - N4BUQ
From: "Barry" <n4buq@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve,
Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing.
Thanks again,
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example. ?Power falls off first on the higherbands as the gain (transconductance) decreases. ?The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load. ?The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <
n4buq@...> wrote:
Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
If R192 in the TR-4C(any) appears heat stressed, check the can cap. Replace R192 with the same value and wattage ¡ª it is a safety for the MV. If you still have the original can, change it ASAP.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, May 18, 2025 at 22:56, VE7PS via groups.io < ve7ps@...> wrote:
Interesting topic about the aging resistors in our 4-line gear.
Any time a rig comes into the shop ALL resistors get visibly?checked, but some get more attention than others.....
Here they are...
All PA screen and cathode resistors on the T-4X(any) and TR-4(any), as we all know.
On the T4XC...R-81 and R91 in plate leads to V-9.? Both are high value resistors which tend to go high with time, reducing plate voltage.? If your audio drive seems low check?these for sure. Also check Plate Voltage on V-9, and if below spec, these resistors are likely the reason.? I found plate voltage on one T-4XC I fixed for a friend years ago at +69VDC on V-9, while spec is +95VDC.? R81 had?gone way?high. Drakes aren't the only rigs I see this?happening to.? K4OAH's "CD's" will help you locate the?resistors, though that's just the start of the fun!? Frankly, ALL resistors with values above?200K or so deserve a resistance?check.? Doesn't seem to be as big an issue on the B-line and?earlier?in this circuit as the circuits are different and resistances are lower....cursory check though, so keep that in mind.
Also on the T-4XC...R49 and R59 on the relay board.? Often seen heat-stressed.
On the TR-4C series...R 192 and R-45 on the relay board.
On all TR-4(any) - R163 on the 200 VDC line to the S meter.? ?It seems to act as a fuse and have found several visibly?open!!!
I'm sure there are more, but this is a start.? I'm sure there are others who can add to the list.
73
Peter
VE7PS
I have found that virtually all of the resistors in my TR-4 have not aged out of tolerance which is a little surprising.? ?I did, though, replace the three 15R cathode resistors.? I think one or two were over 20 ohms but I replaced them mainly because they were no longer all the same value.
Since R13 is "selected", then I presume one can read the bands and should be able to check whether it's out of tolerance.? At least R45 is not "selected".
Thanks for the tip!
Barry - N4BUQ (the other, other Barry)
Barry,
Something else to consider - Every TR-n that I've worked on has had the plate current meter resistors aged high.? The result is that plate current measurement is not correct which of course means that idle current is not set correctly.? Seems to me that idle current is the basic foundation for everything and if its not right than there may be some odd things happen.? There are two resistors.? One is a standard value and the other is determined by the Drake tech during final alignment before the radio was shipped.
Also, I don't recall if you mentioned checking it or not but the 68ohm and 15ohm resistors under the amp tubes are also prone to aging high.? I always check and usually replace those resistors and then measure the resistors for the meter and replace if they have drifted.? You can of course verify your idle current by measuring resistance and voltage drop across the three resistors under the amp tubes, calculating the current draw, and adding up the current draw for all three.
73,
Another Barry
KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <
n4buq@...> wrote:
I tested all three tubes for gas and none were bad in that respect.? Interestingly, I decided to perform the "LIFE TEST" where the filament voltage is reduced (I think it goes down to about 5.8V or maybe 5.9V for a 6.3V filament).? While transconductance drops by an acceptable amount when that button is pressed, the fall in value looked a lot like what I see for plate current when the key is down.
With all the tubes back in place, I decided to monitor the filament voltage.? I've been running the rig between 110VAC and 115VAC and that was giving me a low-to-start-with filament voltage of just under 6VAC.? With that, key-down would cause that voltage to drop to around 5.7VAC.? I then bumped the autotransformer up to closer to 120VAC which gave me very close to 6.3VAC and, oddly enough, on key-down, that voltage would drop just a small amount - perhaps 0.1VAC to 0.2VAC.? That seems a bit odd that the sag was smaller but, perhaps, the transformer is more efficient at the input voltage closer to 120VAC but that's just a guess.
Also, with the input voltage closer to 120VAC, I think I'm seeing a good increase in plate current at resonance.? I suppose that's expected since the plate voltage also climbs with that input voltage.
Thanks,
Barry - N4BUQ
From: "Barry" <
n4buq@...>
To: "DRAKE-RADIO" <
[email protected]>
Sent: Sunday, May 18, 2025 1:03:51 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Richard, Steve,
Thank you both for the responses.? I wasn't sure if "soft" was just a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of excess gas (e.g. white coating or a "getter-like" spot but that's not a very good indicator of small gas amounts.? I'm going to pull them again and run the gas test as I didn't do that when I was testing them.? Maybe that will be revealing.
Thanks again,
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via
" <w1es=
[email protected]>
To: "DRAKE-RADIO" <
[email protected]>
Sent: Sunday, May 18, 2025 12:37:22 PM
Subject: Re: [DRAKE-RADIO] TR-4 - Soft Finals?
Yep, that sounds like a textbook example.? Power falls off first on the higherbands as the gain (transconductance) decreases.? The electrons are generated at the heated cathode and eventually, the cathode material gets depleted.
I¡¯m starting to think that my TR-4Cw RIT is having similar issues, though strangely, the output only sags when on the antenna and not on the dummy load.? The tubes in it are well-used.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, May 17, 2025 at 10:46 PM, n4buq <
n4buq@...> wrote:
Can someone please tell me what is meant by the term "soft finals"? I'm still having problems getting proper output from my TR-4 and, for all I know, that might be the problem. I've tested them for transconductance and all three are very close to the same value and, furthermore, that value is quite a bit above the minimum for a good tube.
Aside from low output (i.e. about 300 mA plate current maximum into a dummy load), I notice that if I hold down the key for a few seconds the plate current tends to drop just slightly and I think if I were to continue holding the key down, the current would continue to slowly decrease.
I measured the voltage across each cathode resistor and I notice the same phenomenon: the voltage climbs to about 1.6 VDC and then begins to drop a bit. Like the transconductance values, each cathode resistor is "matched" in value and behavior to the other two so I suppose that's one good thing.
Am I seeing the result of weak/soft tubes or is something else going on that would cause this?
Thanks,
Barry - N4BUQ
|
On Mon, May 19, 2025 at 06:11 AM, Steve Wedge, W1ES/4 wrote:
My mains can get to 126, so I set my variac to around 118. It doesn¡¯t hurt.
?
?
Ditto.? I use a Superior Electric "Variac" mounted under the operating desktop, within easy reach to make line voltage adjustments. ?Voltage is monitored with a Viz (formerly RCA) WV-120B line voltage monitor.
This setup is only used for boatanchor gear.? 110V for pre-WWII gear, 115V for gear made until about 1975, then 120V thereafter.? ? Additionally, a hospital-grade toroid isolation transformer with multiple receptacles follows the Variac device.? Photos attached.? Paul, W9AC
 
?
|
My shack is converted from an ¡°extra¡± bedroom in the finished part of my cellar and my ¡°stockroom¡± is the large walk-in closet. Lots of room for parts. I have a mixture of older and new parts and I¡¯ll test the older ones before use.?
Before I got these bins back from my friend (long story) I had a 1/2W assortment that I bought on Amazon. Those are standard values but are 1% tolerance.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, May 19, 2025 at 07:04, George Cortez Jr via groups.io < ne2i@...> wrote:
Speaking of resistors, Where are you sourcing your resistors??
?
Thanks
?
George NE2I
|
I had a similar problem with R111 (3.3K 1/2W) series resistor in my
TR3 that
overheated and burnt in half, lots of smoke. The cause of the
overheating of
R111 was C145B, 60ufd 250VDC capacitor in C145 can. It didn't show a
short
with an ohm meter but under voltage it shorted causing R111 to
overheat.
Not only did C145B short internally under voltage but the
capacitance value of
C145B had increased from 60ufd to "108ufd", an "80% increase" in
capacitance
value, C145B in my TR3 not only took out TR3's R111 but it also took
out R4 in
the AC3 power supply resulting in complete loss of +250VDC LV
supply.
If R192 in the TR4C is getting hot then it's quite possible C145A
20ufd can
capacitor is going bad. I agree, replace C145 can capacitor before
it takes
out R192 and quite possibly the AC power supply LV supply.
73
Mike W5RKL
On 5/19/25 8:21 AM, Steve Wedge, W1ES/4
via groups.io wrote:
toggle quoted message
Show quoted text
If R192 in the TR-4C(any) appears heat stressed,
check the can cap. Replace R192 with the same value and wattage
¡ª it is a safety for the MV. If you still have the original can,
change it ASAP.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, May 18, 2025 at 22:56, VE7PS via groups.io <ve7ps@...> wrote:
Interesting topic about the aging resistors in
our 4-line gear.
Any time a rig comes into the shop ALL resistors get
visibly?checked, but some get more attention than
others.....
Here they are...
All PA screen and cathode resistors on the T-4X(any) and
TR-4(any), as we all know.
On the T4XC...R-81 and R91 in plate leads to V-9.? Both
are high value resistors which tend to go high with time,
reducing plate voltage.? If your audio drive seems low
check?these for sure. Also check Plate Voltage on V-9, and
if below spec, these resistors are likely the reason.? I
found plate voltage on one T-4XC I fixed for a friend years
ago at +69VDC on V-9, while spec is +95VDC.? R81 had?gone
way?high. Drakes aren't the only rigs I see this?happening
to.? K4OAH's "CD's" will help you locate the?resistors,
though that's just the start of the fun!? Frankly, ALL
resistors with values above?200K or so deserve a
resistance?check.? Doesn't seem to be as big an issue on the
B-line and?earlier?in this circuit as the circuits are
different and resistances are lower....cursory check though,
so keep that in mind.
Also on the T-4XC...R49 and R59 on the relay board.?
Often seen heat-stressed.
On the TR-4C series...R 192 and R-45 on the relay board.
On all TR-4(any) - R163 on the 200 VDC line to the S
meter.? ?It seems to act as a fuse and have found several
visibly?open!!!
I'm sure there are more, but this is a start.? I'm sure
there are others who can add to the list.
73
Peter
VE7PS
I have found that virtually all of the resistors
in my TR-4 have not aged out of tolerance which is a
little surprising.? ?I did, though, replace the three
15R cathode resistors.? I think one or two were over
20 ohms but I replaced them mainly because they were
no longer all the same value.
Since R13 is "selected", then I presume one can
read the bands and should be able to check whether
it's out of tolerance.? At least R45 is not
"selected".
Thanks for the tip!
Barry - N4BUQ (the other, other Barry)
Barry,
Something else to consider - Every
TR-n that I've worked on has had the plate
current meter resistors aged high.? The result
is that plate current measurement is not correct
which of course means that idle current is not
set correctly.? Seems to me that idle current is
the basic foundation for everything and if its
not right than there may be some odd things
happen.? There are two resistors.? One is a
standard value and the other is determined by
the Drake tech during final alignment before the
radio was shipped.
Also, I don't recall if you
mentioned checking it or not but the 68ohm and
15ohm resistors under the amp tubes are also
prone to aging high.? I always check and usually
replace those resistors and then measure the
resistors for the meter and replace if they have
drifted.? You can of course verify your idle
current by measuring resistance and voltage drop
across the three resistors under the amp tubes,
calculating the current draw, and adding up the
current draw for all three.
73,
Another Barry
KJ5GQM
On Sunday, May 18, 2025 at 05:23:44 PM
CDT, n4buq < n4buq@...>
wrote:
I tested all three tubes for gas
and none were bad in that respect.?
Interestingly, I decided to perform
the "LIFE TEST" where the filament
voltage is reduced (I think it goes
down to about 5.8V or maybe 5.9V for
a 6.3V filament).? While
transconductance drops by an
acceptable amount when that button
is pressed, the fall in value looked
a lot like what I see for plate
current when the key is down.
With all the tubes back in
place, I decided to monitor the
filament voltage.? I've been running
the rig between 110VAC and 115VAC
and that was giving me a
low-to-start-with filament voltage
of just under 6VAC.? With that,
key-down would cause that voltage to
drop to around 5.7VAC.? I then
bumped the autotransformer up to
closer to 120VAC which gave me very
close to 6.3VAC and, oddly enough,
on key-down, that voltage would drop
just a small amount - perhaps 0.1VAC
to 0.2VAC.? That seems a bit odd
that the sag was smaller but,
perhaps, the transformer is more
efficient at the input voltage
closer to 120VAC but that's just a
guess.
Also, with the input voltage
closer to 120VAC, I think I'm seeing
a good increase in plate current at
resonance.? I suppose that's
expected since the plate voltage
also climbs with that input voltage.
Thanks,
Barry - N4BUQ
From: "Barry" < n4buq@...>
To: "DRAKE-RADIO" < [email protected]>
Sent: Sunday, May 18, 2025
1:03:51 PM
Subject: Re: [DRAKE-RADIO]
TR-4 - Soft Finals?
Richard, Steve,
Thank you both for the
responses.? I wasn't sure if
"soft" was just a generic for
"weak" and, in general, maybe
that's true.
My three tubes do not
exhibit some of the more
obvious signs of excess gas
(e.g. white coating or a
"getter-like" spot but that's
not a very good indicator of
small gas amounts.? I'm going
to pull them again and run the
gas test as I didn't do that
when I was testing them.?
Maybe that will be revealing.
Thanks again,
Barry - N4BUQ
From: "Steve Wedge,
W1ES/4 via "
<w1es= [email protected]>
To: "DRAKE-RADIO"
< [email protected]>
Sent: Sunday, May
18, 2025 12:37:22 PM
Subject: Re:
[DRAKE-RADIO] TR-4 - Soft
Finals?
Yep, that sounds like
a textbook example.? Power
falls off first on the
higherbands as the gain
(transconductance)
decreases.? The electrons
are generated at the
heated cathode and
eventually, the cathode
material gets depleted.
I¡¯m starting to think
that my TR-4Cw RIT is
having similar issues,
though strangely, the
output only sags when on
the antenna and not on the
dummy load.? The tubes in
it are well-used.
Steve Wedge, W1ES
Time flies like an
arrow. Fruit flies
like a banana.
On Sat, May 17, 2025 at
10:46 PM, n4buq < n4buq@...>
wrote:
Can someone
please tell me what is
meant by the term "soft
finals"? I'm still having
problems getting proper
output from my TR-4 and,
for all I know, that might
be the problem. I've
tested them for
transconductance and all
three are very close to
the same value and,
furthermore, that value is
quite a bit above the
minimum for a good tube.
Aside from low output
(i.e. about 300 mA plate
current maximum into a
dummy load), I notice that
if I hold down the key for
a few seconds the plate
current tends to drop just
slightly and I think if I
were to continue holding
the key down, the current
would continue to slowly
decrease.
I measured the voltage
across each cathode
resistor and I notice the
same phenomenon: the
voltage climbs to about
1.6 VDC and then begins to
drop a bit. Like the
transconductance values,
each cathode resistor is
"matched" in value and
behavior to the other two
so I suppose that's one
good thing.
Am I seeing the result of
weak/soft tubes or is
something else going on
that would cause this?
Thanks,
Barry - N4BUQ
|
Paul Christensen