|
In comparing early and later R4C power supply schematics, a capacitor (C201) was added going from the output of the low voltage diodes to the high end of the filament string. It is listed as 20uf 150V. I am attaching a schematic showing it. I was wondering what its purpose was and why it was added. Does anyone have any ideas? I thought it might have something to do with audio hum.?
?
Doug, WA3DSP
|
Doug,
?
Yes it had to do with reducing audio hum.? The whole power supply was poorly designed from day one with too much ripple in the 150 volt, -70 volt and 14 volt
supplies.? In this case I think it reduced 120 Hz hum and made 60 Hz hum worse which wasn’t reproduced as well by the speaker.?
?
I must have sold 500 or more total replacement power supply boards that got rid of the ripple (hum) and eliminated the two 5-watt dropping resistors.?? Once
the 12-volt three-terminal regulator came along, I never understood why Drake never redesigned the power supply.? Eliminating the heat from those two dropping resistors, plus replacing the power? hog audio amplifier, made the PTO more stable. ?The replacement
boards were the RPS-4 and AMP-4.
?
Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 12:02 PM
To: [email protected]
Subject: [DRAKE-RADIO] R4C power supply question
?
In comparing early and later R4C power supply schematics, a capacitor (C201) was added going from the output of the low voltage diodes to the high end of the filament string. It is listed as 20uf 150V. I am attaching a schematic showing
it. I was wondering what its purpose was and why it was added. Does anyone have any ideas? I thought it might have something to do with audio hum.?
?
Doug, WA3DSP
|
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to the 7812 to about 14.5-15 volts and the 7812 loafs along.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of #30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
Doug, WA3DSP
|
Doug, I had the same issue with the filament voltages on my R4-C. I coiled up (I am guessing about 6 ft) of small gauge hookup wire and trimmed it to get the correct voltage. The coil was about 1 1/2 diameter and I just laid it down next to the PS board. There are a number of sharp edges in that area and I felt better using insulated hookup wire instead of enameled wire.
On Tue, Mar 21, 2023 at 11:28?PM Doug Crompton WA3DSP < wa3dsp@...> wrote: Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to the 7812 to about 14.5-15 volts and the 7812 loafs along.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of #30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
Doug, WA3DSP
|
Doug,
By the looks of it, production ended in 1979.??
The last one that Ron has listed is 29306, so there are probably some higher than that, but not many I suspect.?
73's,
Mark, WB0IQK
|
Hi Doug,
?
Please see comments inserted below.
?
Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to
the 7812 to about 14.5-15 volts and the 7812 loafs along.
?
Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.? I used the LM-383T which puts out more power than the
LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the
pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
?
Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.? That is likely what you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of
#30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on most of the hundreds of R-4Cs that came through my shop.? I
recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have
had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
?
Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The TR-7 wasn’t any better with all the heat in regulators sinked
to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power transformer oriented 90 degrees from where it is in the R-4C.?
In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related sidebands.? If you remove the R-4C power transformer, punch two
new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached PDF from my 2012 Drake Dayton Forum presentation.
?
COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have been drastically reduced, decreasing assembly time and cost.?
The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid of the 3rd mixer.? That didn’t happen with the 6HS6
circuit. ?Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had been more proactive whether the TR-8 would? have had a chance in
the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8. ?Was it designed well?? I? have no idea. ?????
?
73, Rob, NC0B
Doug, WA3DSP
|
Rob, ? I don’t recall if you and I reached the same but independent conclusions at the same time, but I discovered the power transformer issue back in 2011 when my R-4C and R-4B underwent thorough upgrades.? However, the transformer fix only affected the R-4C.? ? Although the root cause is different, and as your slides show, it has the classic characteristics of so-called “hum modulation,” essentially FM-like sidebands at 60 Hz intervals.? I first noticed it on my R-4C when listening to the crystal calibrator up at 500 kHz on the top end of the PTO.? As the PTO is adjusted toward the 500 kHz end, the ferrite core moves closer to the power transformer.? That coupled with the wrong transformer orientation creates this effect in the R-4C, sometimes even after separately grounding the PTO case. ? I think the reason this had gone unnoticed for decades is because the CW portion of the bands are at the other extreme of the PTO ferrite core position.? If the reverse were true (i.e., CW portion at the high end of the bands), no doubt some folks would have picked up on this limitation much sooner.? Hum modulation effects are much more apparent when listening in CW mode than when listening to SSB transmissions although when bad enough it makes voice sound “fuzzy.” ? After the transformer mod, 60 Hz sidebands are diminished to the point of inaudibility.? It would probably be wrong for everyone to start modifying their R-4C receivers.? As a rule, I get deeply perturbed by the presence of any hum or buzz in receiver audio.? Shortly after working on the Drake receivers, I moved on to Collins 75S-3A and 75S-3C C receivers and eliminated hum in those receivers but it took many hours of work.? On my bench at the moment is a Hallicrafters SR-400A “Cyclone III” transceiver that will soon get the same treatment. ? Paul, W9AC ? ? tom: [email protected] <[email protected]> On Behalf Of Rob Sherwood
Sent: Wednesday, March 22, 2023 1:00 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question ? Hi Doug, ? Please see comments inserted below. ? Rob, NC0B ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question ? Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to the 7812 to about 14.5-15 volts and the 7812 loafs along. ? Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.? I used the LM-383T which puts out more power than the LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the pot disconnected. It is very low level, but being a purist, I was looking for possible fixes. ? Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.? That is likely what you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of #30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so. Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on most of the hundreds of R-4Cs that came through my shop.? I recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
? Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The TR-7 wasn’t any better with all the heat in regulators sinked to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power transformer oriented 90 degrees from where it is in the R-4C.? In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related sidebands.? If you remove the R-4C power transformer, punch two new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached PDF from my 2012 Drake Dayton Forum presentation. ? COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have been drastically reduced, decreasing assembly time and cost.? The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid of the 3rd mixer.? That didn’t happen with the 6HS6 circuit. ?Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had been more proactive whether the TR-8 would? have had a chance in the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8. ?Was it designed well?? I? have no idea. ????? ? 73, Rob, NC0B
Doug, WA3DSP
|
I would first have to determine if this is actually a problem in my R4C but I doubt I would go to the trouble of reorienting the transformer. I have a large piece of mumetal somewhere that we used in our magnetic disk test equipment. It would be interesting to see if a piece of that between the transformer and the PTO would help.
Doug, WA3DSP
|
I definitely noticed the hash on the audio when I bought my first later-production R-4C and spent a fair amount of time trying to tame it.? The location of that third mixer and its design meant that very small differences in shield locations, variations in individual 6EJ7 tubes, etc., were critical to how well the 3rd mixer worked.? I was lucky in that doing the Sartori circuit tamed it enough that I could ignore whatever artefacts were still there.? The early R-4C, with the 6HS6 mixers, didn't have this issue at all.? I agree that the performance of that mixer really threw a wet blanket on the whole experience but I did keep that C Line for a few years and even did some contesting with it.? By that time, we were starting to hear the siren song of the Kenwood TS-930S and I made the switch in the late 80s.
I have since discovered that one can cherrypick 6EJ7's from a bunch of NOS tubes and get one that reduces the hash almost enough to not need to change any circuitry.
I still love the sharpness of the R-4C filters and have a C Line that works pretty well, stone-stock.
73,
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
------- Original Message -------
On Wednesday, March 22nd, 2023 at 12:59 PM, Rob Sherwood <rob@...> wrote:
Hi Doug,
?
Please see comments inserted below.
?
Rob, NC0B
?
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to
the 7812 to about 14.5-15 volts and the 7812 loafs along.
?
Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.? I used the LM-383T which puts out more power than the
LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the
pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
?
Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.? That is likely what you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of
#30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on most of the hundreds of R-4Cs that came through my shop.? I
recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have
had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
?
Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The TR-7 wasn’t any better with all the heat in regulators sinked
to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power transformer oriented 90 degrees from where it is in the R-4C.?
In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related sidebands.? If you remove the R-4C power transformer, punch two
new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached PDF from my 2012 Drake Dayton Forum presentation.
?
COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have been drastically reduced, decreasing assembly time and cost.?
The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid of the 3rd mixer.? That didn’t happen with the 6HS6
circuit. ?Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had been more proactive whether the TR-8 would? have had a chance in
the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8. ?Was it designed well?? I? have no idea. ?????
?
73, Rob, NC0B
Doug, WA3DSP
|
Hi Paul,
Comments inserted below.
Ro
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Paul Christensen
Sent: Wednesday, March 22, 2023 11:27 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
?
I don’t recall if you and I reached the same but independent conclusions at the same time, but I discovered the power transformer issue back in 2011 when my R-4C and R-4B underwent
thorough upgrades.? However, the transformer fix only affected the R-4C.
?
Reply:? We must have arrived at the same conclusion and solution independently.? First I tried some mu metal shielding to no avail, and my R-4C was likely modified
sometime in 2011 before my 2012 Hamvention presentation. ?The hum sidebands, solder braid and grounding solder lug improvement were in my 2010 Drake Forum presentation with attribution where appropriate.? My original R-4, when I was in high school, needed
a better ground than provided by the PTO spring .? As a 16 or 17 ?year old I demonstrated the problem to Drake at the factory and was blown off as a “snot nosed kid”.? Hi Hi? ??They replaced my PTO saying the newer production PTOs had harder ball bearings
that provided a better ground.? Drake never put the flexible grounding braid on the PTO into production until late TR-7s.? ?
?
?
Although the root cause is different, and as your slides show, it has the classic characteristics of so-called “hum modulation,” essentially FM-like sidebands at 60 Hz intervals.?
I first noticed it on my R-4C when listening to the crystal calibrator up at 500 kHz on the top end of the PTO.? As the PTO is adjusted toward the 500 kHz end, the ferrite core moves closer to the power transformer.? That coupled with the wrong transformer
orientation creates this effect in the R-4C, sometimes even after separately grounding the PTO case.
?
Reply:? No question about that.
?
I think the reason this had gone unnoticed for decades is because the CW portion of the bands are at the other extreme of the PTO ferrite core position.? If the reverse were
true (i.e., CW portion at the high end of the bands), no doubt some folks would have picked up on this limitation much sooner.? Hum modulation effects are much more apparent when listening in CW mode than when listening to SSB transmissions although when bad
enough it makes voice sound “fuzzy.”
?
Reply:? I agree, but I found the effect on “fuzzy” SSB unacceptable, too.? I wasn’t doing much CW in those days.?? ??
?
After the transformer mod, 60 Hz sidebands are diminished to the point of inaudibility.? It would probably be wrong for everyone to start modifying their R-4C receivers.?
?
Reply:? Yes likely too much trouble, but if an R-4C owner is a nitpicker like you and I the difference is very significant.
?
As a rule, I get deeply perturbed by the presence of any hum or buzz in receiver audio.? Shortly after working on the Drake receivers, I moved on to Collins 75S-3A and 75S-3C
C receivers and eliminated hum in those receivers but it took many hours of work.?
?
Reply:? I eventually owned an S Line and spent a few years “fixing” some of its issues.? PDFs attached.?
?
On my bench at the moment is a Hallicrafters SR-400A “Cyclone III” transceiver that will soon get the same treatment.
?
Comment:? I briefly owned a Squires Sanders SS-1R and modified it to cover 160 meters.? Unfortunately I sold it before I started testing receivers.? I have
always wondered how well it would? have performed from a noise floor and dynamic range standpoint.? See link to the receiver.? http://www.w1vd.com/SS-1R.html
?
73, Rob, NC0B
?
?
Paul, W9AC
?
?
tom: [email protected]
<[email protected]> On Behalf Of Rob Sherwood
Sent: Wednesday, March 22, 2023 1:00 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Hi Doug,
?
Please see comments inserted below.
?
Rob, NC0B
?
From:
[email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to
the 7812 to about 14.5-15 volts and the 7812 loafs along.
?
Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.? I used the LM-383T which puts out more power than the
LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the
pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
?
Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.? That is likely what
you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of
#30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on most of the hundreds of R-4Cs that came through my shop.? I
recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have
had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
?
Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The TR-7 wasn’t any better with all the heat in regulators sinked
to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power transformer oriented 90 degrees from where it is in the R-4C.?
In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related sidebands.? If you remove the R-4C power transformer, punch two
new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached PDF from my 2012 Drake Dayton Forum presentation.
?
COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have been drastically reduced, decreasing assembly time and cost.?
The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid of the 3rd mixer.? That didn’t happen with the 6HS6
circuit. ?Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had been more proactive whether the TR-8 would? have had a chance in
the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8. ?Was it designed well?? I? have no idea. ?????
?
73, Rob, NC0B
Doug, WA3DSP
|
Hi Doug,
?
I tried mu metal shielding but to no avail.? Yes rotating the transformer is tedious, but it solves the problem.? There is quite a variation from R-4C to R-4C
and I have? no idea why.? That said they are all bad from my perspective, just some worse than others.
?
Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Wednesday, March 22, 2023 11:50 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
I would first have to determine if this is actually a problem in my R4C but I doubt I would go to the trouble of reorienting the transformer. I have a large piece of mumetal somewhere that we used in our magnetic disk test equipment. It
would be interesting to see if a piece of that between the transformer and the PTO would help.
Doug, WA3DSP
|
Hi Steve,
?
I used the Sartori “sold tubes” in the 3rd mixer position for a while until he went out of production.? Then I designed my MIX-4 replacement.? There
were two versions with different mixer components (40673 & later the SA602).?
?
Before I figured out how RFI hash was getting into the 3rd mixer I used a 1:1 120 volt shielded isolation transformer to keep the hash from getting
to the receiver.
?
Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Steve Wedge, W1ES/4 via groups.io
Sent: Wednesday, March 22, 2023 11:58 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
I definitely noticed the hash on the audio when I bought my first later-production R-4C and spent a fair amount of time trying to tame it.? The location of that third mixer
and its design meant that very small differences in shield locations, variations in individual 6EJ7 tubes, etc., were critical to how well the 3rd mixer worked.? I was lucky in that doing the Sartori circuit tamed it enough that I could ignore whatever artefacts
were still there.? The early R-4C, with the 6HS6 mixers, didn't have this issue at all.? I agree that the performance of that mixer really threw a wet blanket on the whole experience but I did keep that C Line for a few years and even did some contesting with
it.? By that time, we were starting to hear the siren song of the Kenwood TS-930S and I made the switch in the late 80s.
I have since discovered that one can cherrypick 6EJ7's from a bunch of NOS tubes and get one that reduces the hash almost enough to not need to change any circuitry.
I still love the sharpness of the R-4C filters and have a C Line that works pretty well, stone-stock.
Time flies like an arrow.? Fruit flies like a banana.
------- Original Message -------
On Wednesday, March 22nd, 2023 at 12:59 PM, Rob Sherwood <rob@...> wrote:
Hi Doug,
?
Please see comments inserted below.
?
Rob, NC0B
?
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to
the 7812 to about 14.5-15 volts and the 7812 loafs along.
?
Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.?
I used the LM-383T which puts out more power than the LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the
pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
?
Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.?
That is likely what you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of
#30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on
most of the hundreds of R-4Cs that came through my shop.? I recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with
the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have
had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
?
Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The
TR-7 wasn’t any better with all the heat in regulators sinked to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power
transformer oriented 90 degrees from where it is in the R-4C.? In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related
sidebands.? If you remove the R-4C power transformer, punch two new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached
PDF from my 2012 Drake Dayton Forum presentation.
?
COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have
been drastically reduced, decreasing assembly time and cost.? The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid
of the 3rd mixer.? That didn’t happen with the 6HS6 circuit. ?Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had
been more proactive whether the TR-8 would? have had a chance in the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8. ?Was it designed well?? I? have no idea. ?????
?
73, Rob, NC0B
Doug, WA3DSP
?
|
" I? never found tube life a problem with the elevated filament voltage. "
I have a vintage text around here somewhere focused specifically on tube (receiving) longevity studies? and among the variables they looked at, filament voltage was the primary driver of reduced usable life.
John
On Wed, Mar 22, 2023 at 2:04?PM Rob Sherwood < rob@...> wrote:
Hi Steve,
?
I used the Sartori “sold tubes” in the 3rd mixer position for a while until he went out of production.? Then I designed my MIX-4 replacement.? There
were two versions with different mixer components (40673 & later the SA602).?
?
Before I figured out how RFI hash was getting into the 3rd mixer I used a 1:1 120 volt shielded isolation transformer to keep the hash from getting
to the receiver.
?
Rob, NC0B
?
From: [email protected] [mailto:[email protected]]
On Behalf Of Steve Wedge, W1ES/4 via
Sent: Wednesday, March 22, 2023 11:58 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
I definitely noticed the hash on the audio when I bought my first later-production R-4C and spent a fair amount of time trying to tame it.? The location of that third mixer
and its design meant that very small differences in shield locations, variations in individual 6EJ7 tubes, etc., were critical to how well the 3rd mixer worked.? I was lucky in that doing the Sartori circuit tamed it enough that I could ignore whatever artefacts
were still there.? The early R-4C, with the 6HS6 mixers, didn't have this issue at all.? I agree that the performance of that mixer really threw a wet blanket on the whole experience but I did keep that C Line for a few years and even did some contesting with
it.? By that time, we were starting to hear the siren song of the Kenwood TS-930S and I made the switch in the late 80s.
I have since discovered that one can cherrypick 6EJ7's from a bunch of NOS tubes and get one that reduces the hash almost enough to not need to change any circuitry.
I still love the sharpness of the R-4C filters and have a C Line that works pretty well, stone-stock.
Time flies like an arrow.? Fruit flies like a banana.
------- Original Message -------
On Wednesday, March 22nd, 2023 at 12:59 PM, Rob Sherwood <rob@...> wrote:
Hi Doug,
?
Please see comments inserted below.
?
Rob, NC0B
?
From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 11:28 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C power supply question
?
Rob,
Yes I completely rebuilt the supply adding a 7812 regulator board which are dirt cheap on Amazon and elsewhere. I also added an LM380 audio board. again, dirt cheap, and everything runs from regulated 12V. I use 3 diodes in series to lower the low voltage to
the 7812 to about 14.5-15 volts and the 7812 loafs along.
?
Reply:? I never used your diode idea, and at least the way I used a copper strap from the 7812 to the chassis, 17 volts into the regulator was a non-issue.?
I used the LM-383T which puts out more power than the LM-380, but 100mW produces plenty of audio with a typical high efficiency speaker. I also used the LM-383T in my SE-3 AM sync detector, but running on 18 volts instead of 12 volts.
My R4C never had the C201 as far as I remember although I ripped quite a bit off the power supply board. There is no heat there anymore. I do have some very low level hum that is coming from somewhere ahead of the volume pot. It is absolutely clean with the
pot disconnected. It is very low level, but being a purist, I was looking for possible fixes.
?
Reply:? My engineer carefully specified how my LM-383T audio amp board had to have a single ground return. Otherwise there would be a ground-loop hum problem.?
That is likely what you are observing.?
I wonder if others have measured filament voltage. I used several digital meters and they all agreed that the filaments were running at about 7.0-7.1 volts. This is with a 121 volt line. I figured I needed about .3 ohms to lower it so I wound about 6 feet of
#30 enameled wire on a high value 2W resistor which dropped it about .5 volts or so.
Reply:? Yes the typical filament voltage is slightly higher than +10% above nominal 6.3 volts on
most of the hundreds of R-4Cs that came through my shop.? I recently was dealing with an R-4C that took 5 minutes to warm up, and the filament voltage was 6.1 volts.? I never came up with a solution to the slow warmup.? I never found tube life a problem with
the elevated filament voltage.?
I was also wondering when the LM380 first came out. The earliest data I can find is an app note dated 1972, so it had to be early in the R4C production, My R4C is SN 28387 which is very close to the end of production in 1976 or later so it certainly could have
had a much better power supply and audio amp at that late date.? Think of the space that would have been saved as most of the powers supply and audio boards would have gone away, I guess by 1976 they were working on the TR7 design which used the newer chips.
?
Reply:? Drake is notorious for using big dropping resistors in products.? Look at the L-4B power supply and all the heat in those large resistors.? The
TR-7 wasn’t any better with all the heat in regulators sinked to the chassis near the PTO.? Also why put the 100 watt PA right by the PTO??? Why put the R-4C power transformer right behind the PTO?? The earlier Drake R-4, R-4A and R-4B receivers had the power
transformer oriented 90 degrees from where it is in the R-4C.? In the R-4C case, the transformer magnetic field couples into the PTO slug-tuned inductor causing hum sidebands on the PTO output. If you operate the PTO outside the radio it has no line-related
sidebands.? If you remove the R-4C power transformer, punch two new holes in the chassis, and remount the transformer 90 degrees from normal (as it is in earlier models), the line-related hum sidebands on the PTO signal are drastically lower.? Please see attached
PDF from my 2012 Drake Dayton Forum presentation.
?
COMMENTS:? Consider the parts count in the TR-7 DR-7 board with all those TTL chips.? The parts count on that board, and likely many others, could have
been drastically reduced, decreasing assembly time and cost.? The change in the R-4C from 6HS6 mixer tubes to 6EJ7s, and the subsequent circuit change for LO injection, was a terrible step backwards.? Any RFI noise on the AC line passed right into the grid
of the 3rd mixer.? That didn’t happen with the 6HS6 circuit.? Drake did well for decades in spite of design errors and the lack of production updates that would have saved money and made the products better. I wonder if the culture at Drake had
been more proactive whether the TR-8 would? have had a chance in the market?? David Assaf W5XU is the TR-8 guru, but I don’t know whether a schematic even exists for the TR-8.? Was it designed well?? I? have no idea. ?????
?
73, Rob, NC0B
Doug, WA3DSP
?
|
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle.
As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs.
There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts.
Many tubes are a limited resource so we need to take care of them!
?
Doug, WA3DSP
|
The extension of lamp and tube life applies to pure tungsten filaments.? These were common in large transmitting tubes.? For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored.? Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers.? These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice.? during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission.
toggle quoted message
Show quoted text
-------- Original message -------- From: Doug Crompton WA3DSP <wa3dsp@...> Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle. As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs. There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts. Many tubes are a limited resource so we need to take care of them! ? Doug, WA3DSP
|
Some of the earliest discussions were by the US Navy that was studying why tubes did not last long.? ?Filament voltage was generally the culprit and gave rise to the +_ 10 % voltage range.? The major culprit is that the older radios were designed for lower input voltages ranging from 110 volts to 115 volts and then to today's? standard of 120.? So a power transformer in an older set? was optimally sized for the input range of that day and use in todays world leads to all voltages in these radios being higher than intended.? For the filament consideration according to the navy study there then was a reduction in useful lifetime.? Tube manufacturers used this fact in designing filaments more tolerant of various voltages ( the 10%) so the result is they last longer but are still challenged in older sets in use today. David Assaf III
W5XU??? VP8RXU
On Thu, Mar 23, 2023, 3:38 AM Richard Knoppow < 1oldlens1@...> wrote: The extension of lamp and tube life applies to pure tungsten filaments.? These were common in large transmitting tubes.? For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored.? Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers.? These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice.? during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission.
-------- Original message -------- Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle. As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs. There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts. Many tubes are a limited resource so we need to take care of them! ? Doug, WA3DSP
|
I measured my line voltage here in central NC and it’s usually 123VAC or thereabouts. I decided that, rather than going through a dozen or so rigs, it was and is much easier to buy a 20A Variac and connect all of the non-amp equipment to it.?
I never have more than 2-3 sets in at any given time and so this works for me. It keeps everything more original and cuts down on stressed parts.?
The Variac I bought was one of those red Chinese ones on Amazon or eBay. Well under $100. And yes, I scraped some paint off some grounding points first. I’ve had no trouble in the several months that it has been installed.?
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
Sent from Proton Mail for iOS
On Thu, Mar 23, 2023 at 07:17, David < david.w5xu@...> wrote: Some of the earliest discussions were by the US Navy that was studying why tubes did not last long. Filament voltage was generally the culprit and gave rise to the +_ 10 % voltage range. The major culprit is that the older radios were designed for lower input voltages ranging from 110 volts to 115 volts and then to today's standard of 120. So a power transformer in an older set was optimally sized for the input range of that day and use in todays world leads to all voltages in these radios being higher than intended. For the filament consideration according to the navy study there then was a reduction in useful lifetime. Tube manufacturers used this fact in designing filaments more tolerant of various voltages ( the 10%) so the result is they last longer but are still challenged in older sets in use today. David Assaf III
W5XU VP8RXU
On Thu, Mar 23, 2023, 3:38 AM Richard Knoppow < 1oldlens1@...> wrote: The extension of lamp and tube life applies to pure tungsten filaments. These were common in large transmitting tubes. For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored. Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers. These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice. during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission.
-------- Original message -------- Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle. As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs. There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts. Many tubes are a limited resource so we need to take care of them! Doug, WA3DSP
|
Steve,
Since that variable transformer can be adjusted to output more than 125V you might consider removing the knob to prevent accidental voltage changes.
On Thu, Mar 23, 2023 at 7:36?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote:
I measured my line voltage here in central NC and it’s usually 123VAC or thereabouts. I decided that, rather than going through a dozen or so rigs, it was and is much easier to buy a 20A Variac and connect all of the non-amp equipment to it.?
I never have more than 2-3 sets in at any given time and so this works for me. It keeps everything more original and cuts down on stressed parts.?
The Variac I bought was one of those red Chinese ones on Amazon or eBay. Well under $100. And yes, I scraped some paint off some grounding points first. I’ve had no trouble in the several months that it has been installed.?
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
Sent from Proton Mail for iOS
On Thu, Mar 23, 2023 at 07:17, David < david.w5xu@...> wrote: Some of the earliest discussions were by the US Navy that was studying why tubes did not last long. Filament voltage was generally the culprit and gave rise to the +_ 10 % voltage range. The major culprit is that the older radios were designed for lower input voltages ranging from 110 volts to 115 volts and then to today's standard of 120. So a power transformer in an older set was optimally sized for the input range of that day and use in todays world leads to all voltages in these radios being higher than intended. For the filament consideration according to the navy study there then was a reduction in useful lifetime. Tube manufacturers used this fact in designing filaments more tolerant of various voltages ( the 10%) so the result is they last longer but are still challenged in older sets in use today. David Assaf III
W5XU VP8RXU
On Thu, Mar 23, 2023, 3:38 AM Richard Knoppow < 1oldlens1@...> wrote: The extension of lamp and tube life applies to pure tungsten filaments. These were common in large transmitting tubes. For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored. Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers. These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice. during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission.
-------- Original message -------- Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle. As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs. There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts. Many tubes are a limited resource so we need to take care of them! Doug, WA3DSP
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Same here, Steve.? A Stacor Variac is used along with a 4-recepticle isolation transformer.? An RCA WV-120B line voltage monitor plugs into one of the receptacles to monitor line voltage while adjusting the Variac to match line voltage with the vintage of the radio.? For example, I set Variac voltage to 110V when using 1930s-era gear like pre-war National and Hammarlund receivers.? Then step it up to 115-117V for 1950s and ‘60s gear like Drake and Collins.? ? The RCA monitor has its own receptacle to power additional equipment if needed.? Having the monitor is a great way to continuously watch line voltage as my utility line voltage varies from 120V to about 127V.? ? Paul, W9AC ?? ?
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From: [email protected] < [email protected]> On Behalf Of Steve Wedge, W1ES/4 via groups.io Sent: Thursday, March 23, 2023 7:36 AM To: [email protected]Subject: Re: [DRAKE-RADIO] R4C power supply question ? I measured my line voltage here in central NC and it’s usually 123VAC or thereabouts. I decided that, rather than going through a dozen or so rigs, it was and is much easier to buy a 20A Variac and connect all of the non-amp equipment to it.? I never have more than 2-3 sets in at any given time and so this works for me. It keeps everything more original and cuts down on stressed parts.? The Variac I bought was one of those red Chinese ones on Amazon or eBay. Well under $100. And yes, I scraped some paint off some grounding points first. I’ve had no trouble in the several months that it has been installed.? Time flies like an arrow. Fruit flies like a banana. Sent from Proton Mail for iOS On Thu, Mar 23, 2023 at 07:17, David <david.w5xu@...> wrote: Some of the earliest discussions were by the US Navy that was studying why tubes did not last long. Filament voltage was generally the culprit and gave rise to the +_ 10 % voltage range. The major culprit is that the older radios were designed for lower input voltages ranging from 110 volts to 115 volts and then to today's standard of 120. So a power transformer in an older set was optimally sized for the input range of that day and use in todays world leads to all voltages in these radios being higher than intended. For the filament consideration according to the navy study there then was a reduction in useful lifetime. Tube manufacturers used this fact in designing filaments more tolerant of various voltages ( the 10%) so the result is they last longer but are still challenged in older sets in use today. David Assaf III
W5XU VP8RXU ? On Thu, Mar 23, 2023, 3:38 AM Richard Knoppow <1oldlens1@...> wrote: The extension of lamp and tube life applies to pure tungsten filaments. These were common in large transmitting tubes. For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored. Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers. These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice. during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission. -------- Original message -------- Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle.
As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs.
There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts.
Many tubes are a limited resource so we need to take care of them!
Doug, WA3DSP
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It is under the desk and so won’t be hit by me. My cats don’t have the strength to turn it :-)
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
Sent from Proton Mail for iOS
On Thu, Mar 23, 2023 at 7:42 AM, Ken, WA2LBI < wa2lbi@...> wrote: Steve,
Since that variable transformer can be adjusted to output more than 125V you might consider removing the knob to prevent accidental voltage changes. On Thu, Mar 23, 2023 at 7:36?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote:
I measured my line voltage here in central NC and it’s usually 123VAC or thereabouts. I decided that, rather than going through a dozen or so rigs, it was and is much easier to buy a 20A Variac and connect all of the non-amp equipment to it.
I never have more than 2-3 sets in at any given time and so this works for me. It keeps everything more original and cuts down on stressed parts.
The Variac I bought was one of those red Chinese ones on Amazon or eBay. Well under $100. And yes, I scraped some paint off some grounding points first. I’ve had no trouble in the several months that it has been installed.
73,
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
Sent from Proton Mail for iOS
On Thu, Mar 23, 2023 at 07:17, David < david.w5xu@...> wrote: Some of the earliest discussions were by the US Navy that was studying why tubes did not last long. Filament voltage was generally the culprit and gave rise to the +_ 10 % voltage range. The major culprit is that the older radios were designed for lower input voltages ranging from 110 volts to 115 volts and then to today's standard of 120. So a power transformer in an older set was optimally sized for the input range of that day and use in todays world leads to all voltages in these radios being higher than intended. For the filament consideration according to the navy study there then was a reduction in useful lifetime. Tube manufacturers used this fact in designing filaments more tolerant of various voltages ( the 10%) so the result is they last longer but are still challenged in older sets in use today. David Assaf III
W5XU VP8RXU
On Thu, Mar 23, 2023, 3:38 AM Richard Knoppow < 1oldlens1@...> wrote: The extension of lamp and tube life applies to pure tungsten filaments. These were common in large transmitting tubes. For receiving tubes the general reccomendation is to keep filament voltage to within about +/- 5%. This applies to tjoriated tungsten also but voyage can be lowered somewhat if emission is monitored. Eimac has authoritative information in their tube application notes. A place where lowered voltage is often found is the filament of the 6H6 and 6AL5 twin diodes when used as detectors an noise clippers. These tubes have a tendency to produce hum which is reduced by lowering filament voltage by about a volt. However in general its not a recommended practice. during WW2 RCA published charts showing the effect of filament voltageon tube life for pure tungsten filaments. I don't off hand remember the numbers but a relatively small reduction increases life substantially with relatively small reduction in emission.
-------- Original message -------- Date: 3/23/23 12:04 AM (GMT-08:00) Subject: Re: [DRAKE-RADIO] R4C power supply question
I am picky about things, but the twins are not going to be rigs I will use a great deal and probably seldom. No doubt the Sherwood updates are top-notch but it just wouldn't be worth it to spend the time and money the way I would operate the receiver. I will leave that to the next guy. I did update the power supply and audio amp which are probably the first things someone with an R4C should tackle. As for the filaments, I did add a self wound resistor to reduce the voltage by about .5 volts. It is now sitting at about 6.5 @ 122 line volts. From what I have read, you don't want to run the filament voltage too low, but too high by a volt is not a good idea either. This greatly depends on your line voltage. Typical today is 120-122, but in some areas it can vary greatly. I remember in the old incandescent light bulb days seeing a chart that showed a bulb would last 10 times longer with 10% less rated voltage and 1/10 the time with 10% more. I don't know if that is true, and tube filaments would probably not directly correlate to the old bulbs. There is a lot of misinformation on the Internet so it is hard to get accurate information since tubes other than in hobby stuff are rarely used anymore. I saw many posts that warned of permanent loss of emission after running low filament voltage, and others saying that tube gain actually improved at lower filament voltage. Of course, we are talking about greatly lower. Keeping filaments between 6.0 and 6.5 volts is a good range to shoot for. It is also a good thing that Drake did not blast the hell out of plate voltage limits like Heath and other manufacturers. There are a couple of miniature tubes in the KWM2 that would give you a burn as bad as touching a soldering iron just by briefly touching. Heath often ran tubes at or higher than maximum ratings. There is no reason to run a receiving tube at 250-300 volts. Many tubes are a limited resource so we need to take care of them! Doug, WA3DSP
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Doug Crompton WA3DSP
Rob Sherwood
Paul Christensen
David