|
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead, seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
Hi Barry
I usually just tune for the dip, and ignore the possibility that there are incremental power gains that might be had with further tuning.? The small additional power didn't seem worth the stress on the tube.
That said, I'm sure someone smart will come along with the right answer :-)
John K5MO
I don't think I've ever owned a power meter and now I have one in my MN-2000.? Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead, seems to occur on the "edge" of that dip.? Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output.? Furthermore, I presume that getting the dip first and then tweaking for maximum output is the most efficient way to run.? Is that correct?? Is what I'm seeing normal?? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote: I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead, seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
Isn¡¯t this behavior discussed under neutralization in the manual? ?Rob, NC0B?
toggle quoted message
Show quoted text
On Apr 3, 2025, at 8:19?AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
?
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands
Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead,
seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output
is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
It certainly is and is exactly what I'm seeing.? Thank you for pointing that out!? I plan to go through the entire alignment soon.
Thanks, Barry - N4BUQ
Isn¡¯t this behavior discussed under neutralization in the manual? ?Rob, NC0B?
On Apr 3, 2025, at 8:19?AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands
Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead,
seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output
is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
Yes, it must be.
All my ham growing up years I understood peak output and current dip occurring at different settings was the primary symptom of poor neutralization.
That reality, and the mantra of >always< dip the plate >last<, were the gotta-haves of tuning up a tube transmitter.
Dan WB4GRA
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Show quoted text
On Apr 3, 2025, at 11:04?AM, Rob Sherwood via groups.io <rob@...> wrote:
?
Isn¡¯t this behavior discussed under neutralization in the manual? ?Rob, NC0B?
On Apr 3, 2025, at 8:19?AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
?
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands
Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead,
seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output
is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
It is NOT normal. It is a sign that the amplifier needs to be neutralized. Plate dip and power peak should be simultaneous. The coincidence of these two is a very sensitive measure of neutralization. For the T-4 and some other models Drake specifies setting the neutralization using the coincidence but if the neutralization is not almost correct this may be a difficult adjustment to make. A better way to check neutralization is to measure the feed through of drive power to the plate by disconnecting the screens of tetrodes or the plates of triodes. Use something sensitive like a receiver or scope to see what is coming through, then set the neutralization adjustment to null it. Once that is adjusted you can check the neutralization via the Drake method, that is see if the plate dip and power peak are simultaneous.
There is a great deal of information on neutralizing on the web. You should be familiar with the theory of what is being done. The idea is roughly to eliminate any positive feedback through the tubes by means of a sort of bridge circuit. It is done to prevent the tubes from oscillating. If that happens the oscillation will be uncontrolled and destroy the tubes. In general neutralization is more critical at higher frequencies. You can get approximate neutralization at, say 20 meters, and then check it at 10 meters making any small adjustments necessary.
BTW, this is not a matter of the type of circuit used to match the output to the antenna, neutralization is necessary for any type of output pi-network or otherwise.
toggle quoted message
Show quoted text
On 4/3/2025 6:53 AM, n4buq wrote: I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead, seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Richard,
If I understand correctly, for the three 6JB6 (tetrodes), I can disconnect the screen connection (one connection goes to all three tubes) and then I can either scope the output or use an HF VTVM at the antenna jack to see the spurious oscillation and null it. Is that correct?
Thanks!
Barry - N4BUQ
toggle quoted message
Show quoted text
It is NOT normal. It is a sign that the amplifier needs to be
neutralized. Plate dip and power peak should be simultaneous. The
coincidence of these two is a very sensitive measure of neutralization.
For the T-4 and some other models Drake specifies setting the
neutralization using the coincidence but if the neutralization is not
almost correct this may be a difficult adjustment to make. A better way
to check neutralization is to measure the feed through of drive power to
the plate by disconnecting the screens of tetrodes or the plates of
triodes. Use something sensitive like a receiver or scope to see what is
coming through, then set the neutralization adjustment to null it. Once
that is adjusted you can check the neutralization via the Drake method,
that is see if the plate dip and power peak are simultaneous.
There is a great deal of information on neutralizing on the web.
You should be familiar with the theory of what is being done. The idea
is roughly to eliminate any positive feedback through the tubes by means
of a sort of bridge circuit. It is done to prevent the tubes from
oscillating. If that happens the oscillation will be uncontrolled and
destroy the tubes. In general neutralization is more critical at higher
frequencies. You can get approximate neutralization at, say 20 meters,
and then check it at 10 meters making any small adjustments necessary.
BTW, this is not a matter of the type of circuit used to match the
output to the antenna, neutralization is necessary for any type of
output pi-network or otherwise.
On 4/3/2025 6:53 AM, n4buq wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000.
Tuning up my TR-4, I notice that maximizing the output power doesn't
necessarily coincide with the "dip" in plate current but, instead, seems to
occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the
dip at its minimum value but now I'm wondering if that wasn't yielding maximum
power output. Furthermore, I presume that getting the dip first and then
tweaking for maximum output is the most efficient way to run. Is that correct?
Is what I'm seeing normal? I presume so but after all these years, I'm
beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
That is correct. You probably want something more sensitive than a VTVM, a scope is ideal but a radio receiver works well. As long as the screens are disconnected little or no power will come out. For tetrodes/pentodes it is not necessary to disconnect the plates. The neutralizing capacitor forms a bridge with the internal capacitances of the tube. When correctly adjusted the bridge nulls out the coupling through the tube. There are better explanations on the web.
You can start at some relatively low frequency, probably 20 meters is suitable, get a null, and then go up to 10 meters (or whatever the maximum frequency is) and refine the adjustment if necessary. The reason for retesting using the Drake method once the screens are reattached is that the Drake method is the most sensitive way to adjust the neutralization. If the screen method is used first you will be right on or very close so there will not be difficulty with the Drake method.
The driver can be adjusted at very low power before doing the neutralization. One problem with the internal feedback is that its possible to get the final amp oscillating is close to full power simply by adjustment of the plate. The warning is that there is power out with no drive and the output does not vary with the drive level. The output stage is NOT amplifying, it is oscillating and can burn up very quickly.
Note that some rigs, notably Kenwood, have switches for the screen voltage especially for neutralizing them. I am only familiar with a couple of Drake rigs but in both the screen feeds are easy to get to and disconnect.
I should not have to add this but better: For triodes it is the plates that should be disconnected. For tetrodes or pentodes disconnect the screens, that will cut the tube off. Do NOT disconnect the plates alone. You can disconnect BOTH screens and plates but disconnecting the plates is not necessary.
Success with this (I think you make your own luck) and please report back on your results.
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Show quoted text
On 4/3/2025 12:41 PM, n4buq wrote: Richard,
If I understand correctly, for the three 6JB6 (tetrodes), I can disconnect the screen connection (one connection goes to all three tubes) and then I can either scope the output or use an HF VTVM at the antenna jack to see the spurious oscillation and null it. Is that correct?
Thanks!
Barry - N4BUQ
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
I meant to add do NOT disconnect the plates of pentodes/tetrodes alone, the screens will try to absorb all the output of the cathode and burn up. If the screens are disconnected the electron flow in the tube will be cut off, which is what you want. Not necessary to disconnect both screens and plates, screens are enough.
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Show quoted text
On 4/3/2025 2:07 PM, Richard Knoppow via groups.io wrote:
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
The neut procedure is but no mention is made of what happens on the lower bands.
Neutralisation is most important at the highest frequencies, I have been told for years.? Being a bit "off" on lower bands is supposedly less critical.
Then we have the 40m oscillations in the TR7, so I guess these items aren't cast in stone.??
For the purposes of the TR-4(any), I'm guessing that 40m neut isn't as important.? There isn't one setting that causes exact plate-dip-max-power-out coincidence on all bands.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Thursday, April 3rd, 2025 at 11:03 AM, Rob Sherwood via groups.io <rob@...> wrote:
Isn¡¯t this behavior discussed under neutralization in the manual? ?Rob, NC0B?
On Apr 3, 2025, at 8:19?AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
?
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands
Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead,
seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output
is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
I took the PA cage off because it had a concavity to it that bothered me since it made the top of the cage that much closer to the plate caps.? I then noticed the neutralization capacitor is fully open.? I don't know if that's necessarily a bad thing but I can't help but think it should have at least a little capacitance.? I'll find out when I get around to adjusting it.
73, Barry - N4BUQ
The neut procedure is but no mention is made of what happens on the lower bands.
Neutralisation is most important at the highest frequencies, I have been told for years.? Being a bit "off" on lower bands is supposedly less critical.
Then we have the 40m oscillations in the TR7, so I guess these items aren't cast in stone.??
For the purposes of the TR-4(any), I'm guessing that 40m neut isn't as important.? There isn't one setting that causes exact plate-dip-max-power-out coincidence on all bands.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Thursday, April 3rd, 2025 at 11:03 AM, Rob Sherwood via groups.io <rob@...> wrote:
Isn¡¯t this behavior discussed under neutralization in the manual? ?Rob, NC0B?
On Apr 3, 2025, at 8:19?AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
Barry, I¡¯ve found with the TR-3/4 that they don¡¯t 100% neutralise on all bands ¡ª especially 40m but sometimes 20m as well. It is unavoidable and the modeling of it is way above my pay grade.?
I still neutralise on the highest 10m band available (newer rigs made the upper two 10m bands
Optional). If all you have is the low 10m band Xtal, run the PTO to 28.6 and neutralise only after checking for coincident dip And max Power out.?
I keep my TR¡¯s at the plate dip, as it¡¯s passing less current. Chances are, you may lose 10-20W output but that difference is probably not detectable at the other end.?
Also, be mindful of ¡°rogue¡± resonances when tuning the driver. Stick within the range shown by the alignment procedure: I.e., if the preset alignment is at 7, avoid any peaks that are at, say, 2.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 09:53, n4buq < n4buq@...> wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000. Tuning up my TR-4, I notice that maximizing the output power doesn't necessarily coincide with the "dip" in plate current but, instead,
seems to occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the dip at its minimum value but now I'm wondering if that wasn't yielding maximum power output. Furthermore, I presume that getting the dip first and then tweaking for maximum output
is the most efficient way to run. Is that correct? Is what I'm seeing normal? I presume so but after all these years, I'm beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
|
Apples and oranges. The TR7 40M problem is a common mode feedback path through the high pass filter module. Tube neutralization deals with only the PA circuit (and occasionally the driver tube has its own neutralization adjustment). On Thu, 03 Apr 2025 23:41:54 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: Then we have the 40m oscillations in the TR7, so I guess these items aren't cast in stone. -- 73 -Jim NU0C
|
I would say your PA is not neutralized, although IIRC the parallel capacitor needed to be changed for a certain brand of tube. Someone else probably knows. On Thu, 3 Apr 2025 21:25:37 -0400 (EDT) "n4buq via groups.io" <n4buq@...> wrote: I then noticed the neutralization capacitor is fully open. I don't know if that's necessarily a bad thing but I can't help but think it should have at least a little capacitance. -- 73 -Jim NU0C
|
Thanks, Jim.
This is concerning:
73,
Barry - N4BUQ
toggle quoted message
Show quoted text
I would say your PA is not neutralized, although IIRC the parallel capacitor
needed to be changed for a certain brand of tube. Someone else probably knows.
On Thu, 3 Apr 2025 21:25:37 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
I then noticed the neutralization capacitor is fully open. I don't know if
that's necessarily a bad thing but I can't help but think it should have at
least a little capacitance.
--
73
-Jim
NU0C
|
Well hey, it lasted 50 years! I have not heard of this failure before. It seems to me to be just an old age failure. Perhaps the collar had a weak spot or something. But by all means, do inspect it or replace it with a better designed cap if it concerns you. Some years back I was called over by a friend who was having netralization issues with his new-to-him TR4. It was a 30 second fix. I peeked in at the capacitor and the end plate had a bent corner that was making it short out. I straightened it out and we neutralized the rig. There was no damage to the rig or operator. It does pay to do a visual inspection first. On Thu, 3 Apr 2025 21:57:53 -0400 (EDT) "n4buq via groups.io" <n4buq@...> wrote: Thanks, Jim.
This is concerning:
73,
Barry - N4BUQ -- 73 -Jim NU0C
|
IIRC, you need a slightly higher value parallel cap with RCA tubes.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 9:50 PM, Jim Shorney via groups.io < jimNU0C@...> wrote:
I would say your PA is not neutralized, although IIRC the parallel capacitor needed to be changed for a certain brand of tube. Someone else probably knows.
On Thu, 3 Apr 2025 21:25:37 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
> I then noticed the neutralization capacitor is fully open. I don't know if that's necessarily a bad thing but I can't help but think it should have at least a little capacitance.
--
73
-Jim
NU0C
|
This one has GE tubes.? Not sure if those are considered the "good" ones (like the Sylvanias) or if they need more capacitance.? Hopefully I'll get to the neutralization adjustment today or tomorrow.
Thanks, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Friday, April 4, 2025 7:17:29 AM
Subject: Re: [DRAKE-RADIO] Tuning a pi-Network Output
IIRC, you need a slightly higher value parallel cap with RCA tubes.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 9:50 PM, Jim Shorney via groups.io <jimNU0C@...> wrote:
I would say your PA is not neutralized, although IIRC the parallel capacitor needed to be changed for a certain brand of tube. Someone else probably knows.
On Thu, 3 Apr 2025 21:25:37 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
> I then noticed the neutralization capacitor is fully open. I don't know if that's necessarily a bad thing but I can't help but think it should have at least a little capacitance.
--
73
-Jim
NU0C
|
The GE tubes are equivalent to the Sylvanias.? No problems.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, April 4th, 2025 at 8:42 AM, n4buq <n4buq@...> wrote:
This one has GE tubes.? Not sure if those are considered the "good" ones (like the Sylvanias) or if they need more capacitance.? Hopefully I'll get to the neutralization adjustment today or tomorrow.
Thanks, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Friday, April 4, 2025 7:17:29 AM
Subject: Re: [DRAKE-RADIO] Tuning a pi-Network Output
IIRC, you need a slightly higher value parallel cap with RCA tubes.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 3, 2025 at 9:50 PM, Jim Shorney via groups.io <jimNU0C@...> wrote:
I would say your PA is not neutralized, although IIRC the parallel capacitor needed to be changed for a certain brand of tube. Someone else probably knows.
On Thu, 3 Apr 2025 21:25:37 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
> I then noticed the neutralization capacitor is fully open. I don't know if that's necessarily a bad thing but I can't help but think it should have at least a little capacitance.
--
73
-Jim
NU0C
|
When there are spurious oscillations in the PA tubes, is there a particular frequency this usually occurs? In other words, does changing bands change the frequency of the oscillation? I'm just wondering what frequency I might try listening to in order to hear them.
Thanks,
Barry - N4BUQ
toggle quoted message
Show quoted text
It is NOT normal. It is a sign that the amplifier needs to be
neutralized. Plate dip and power peak should be simultaneous. The
coincidence of these two is a very sensitive measure of neutralization.
For the T-4 and some other models Drake specifies setting the
neutralization using the coincidence but if the neutralization is not
almost correct this may be a difficult adjustment to make. A better way
to check neutralization is to measure the feed through of drive power to
the plate by disconnecting the screens of tetrodes or the plates of
triodes. Use something sensitive like a receiver or scope to see what is
coming through, then set the neutralization adjustment to null it. Once
that is adjusted you can check the neutralization via the Drake method,
that is see if the plate dip and power peak are simultaneous.
There is a great deal of information on neutralizing on the web.
You should be familiar with the theory of what is being done. The idea
is roughly to eliminate any positive feedback through the tubes by means
of a sort of bridge circuit. It is done to prevent the tubes from
oscillating. If that happens the oscillation will be uncontrolled and
destroy the tubes. In general neutralization is more critical at higher
frequencies. You can get approximate neutralization at, say 20 meters,
and then check it at 10 meters making any small adjustments necessary.
BTW, this is not a matter of the type of circuit used to match the
output to the antenna, neutralization is necessary for any type of
output pi-network or otherwise.
On 4/3/2025 6:53 AM, n4buq wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000.
Tuning up my TR-4, I notice that maximizing the output power doesn't
necessarily coincide with the "dip" in plate current but, instead, seems to
occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the
dip at its minimum value but now I'm wondering if that wasn't yielding maximum
power output. Furthermore, I presume that getting the dip first and then
tweaking for maximum output is the most efficient way to run. Is that correct?
Is what I'm seeing normal? I presume so but after all these years, I'm
beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Rob Sherwood
Jim Shorney