?

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 3^rd 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

On Mar 22, 2023, at 10:34 AM, Mark - WB0IQK via groups.io <mgilger@...> wrote:

?There are 3 vintage nets held on 14.292.5 every Sunday.? If someone wanted to start a Drake net how about either 2pm or 6pm eastern? Would have to coordinate with the NCS's of those nets to let them know as they sometimes tend to run over their hour time slot.?

3pm Eastern = Vintage SSB net
4pm Eastern = Heathkit net
5pm Eastern = Swan net

73's,
Mark, WB0IQK

On Mar 22, 2023, at 10:34 AM, Mark - WB0IQK <mgilger@...> wrote:

?There are 3 vintage nets held on 14.292.5 every Sunday.? If someone wanted to start a Drake net how about either 2pm or 6pm eastern? Would have to coordinate with the NCS's of those nets to let them know as they sometimes tend to run over their hour time slot.?

3pm Eastern = Vintage SSB net
4pm Eastern = Heathkit net
5pm Eastern = Swan net

73's,
Mark, WB0IQK

From: "Dave Edwards" <kd2e@...>
To: "DRAKE-RADIO" <[email protected]>
Cc: "Gary Follett" <xntrick1948@...>
Sent: Wednesday, March 22, 2023 6:51:25 AM
Subject: Re: [DRAKE-RADIO] 2-C Receiver

I would first check really carefully...with a loupe or magnifying glass,
and a STRONG light to see if the existing knob is not already split perhaps.

As far as the control itself...I would avoid spray stuff.

I'd suggest a thin oil, with a toothpick. study the control carefully,
finding the bearing points. Drop one drop of oil wherever you see the
point where something supports the rotation (perhaps front and rear
bearing??)

Again, a strong lamp is key. Be nice to the 2C. It is an amazing, and
trailblazing rig!!

...Dave? KD2E

On 3/21/23 5:17 PM, Dave via groups.io wrote:

Gary, Dave, John,

Thanks for the replies!

I removed the knob this afternoon and it is in good shape.
It looks like the set screw presses against a fiber like bushing that
surrounds the shaft and this presses against the shaft for a tight fit.
It did not feel stuck but I cannot turn it by just grabbing the shaft
with my fingers.
The shaft is round without a flat spot so I guess it is just a tight
compression fit that does the work.
I can move the switch to all three positions with a pair of pliers and
LSB/USB works just fine !!!

I may open it up and look at the underside and then try some lubricant
of some sort on the shaft, any suggestions?
I have WD40 & PB Blaster here to loosen it up some to start but maybe
some kind of light oil after that?

Dave KC3AM

On 3/20/2023 9:50 PM, Gary Follett wrote:

That knob? should most certainly operate with a click at each
position, allowing reception of AM, USB and LSB/CW.

There are two possibilities. One is simple, that the set screw for
the knob is loose. I think this is a setscrew type knob…

If the set screw is very tight but you still cannot get a switch
action, remove the knob and have a look at the shaft. Try to turn it
gently with a pliers. If you get the same result, remove the cover
and have a look at the coupling between the small inner shaft and the
switch behind it to see if it is loose or broken. That coupling is
below the chassis (underside) towards the back, with the shaft going
between the coils of the bandpass filter coils.

Try that. If no joy, I have the last possibility you. Don’t want to
hear unless you are really good at repair work.

Gary

W0DVN

On Mar 20, 2023, at 8:28 PM, Dave via groups.io
<kc3am@...> wrote:

Hello everyone,

Last summer I picked up a 2-C to go with my 2-NT.
I have been using it for CW without any troubles.
I tried to listen to some SSB signals tonight and I found a problem...

I cannot tune in the SSB signals, the mode control just spins around
and has no effect.

This is the first time I have tried to listen to SSB so this is new
to me.

Looking at the schematic before I open it up it looks like the mode
switch should have a few positions to it and not just spin around.

Am I correct?

Thanks much,

Dave KC3AM

We tried a 20 meter net many years ago and it never worked out. Very limited check-ins.? We also had a 75m swap net and had to disband that some years ago due to lack of participation.?

73's,
Mark, WB0IQK?

Gary, Dave, John,

Thanks for the replies!

I removed the knob this afternoon and it is in good shape.
It looks like the set screw presses against a fiber like bushing that surrounds the shaft and this presses against the shaft for a tight fit.
It did not feel stuck but I cannot turn it by just grabbing the shaft with my fingers.
The shaft is round without a flat spot so I guess it is just a tight compression fit that does the work.
I can move the switch to all three positions with a pair of pliers and LSB/USB works just fine !!!

I may open it up and look at the underside and then try some lubricant of some sort on the shaft, any suggestions?
I have WD40 & PB Blaster here to loosen it up some to start but maybe some kind of light oil after that?

Dave KC3AM

On 3/20/2023 9:50 PM, Gary Follett wrote:

That knob? should most certainly operate with a click at each position, allowing reception of AM, USB and LSB/CW.

There are two possibilities. One is simple, that the set screw for the knob is loose. I think this is a setscrew type knob…

If the set screw is very tight but you still cannot get a switch action, remove the knob and have a look at the shaft. Try to turn it gently with a pliers. If you get the same result, remove the cover and have a look at the coupling between the small inner shaft and the switch behind it to see if it is loose or broken. That coupling is below the chassis (underside) towards the back, with the shaft going between the coils of the bandpass filter coils.

Try that. If no joy, I have the last possibility you. Don’t want to hear unless you are really good at repair work.

Gary

W0DVN

On Mar 20, 2023, at 8:28 PM, Dave via groups.io <kc3am@...> wrote:

Hello everyone,

Last summer I picked up a 2-C to go with my 2-NT.
I have been using it for CW without any troubles.
I tried to listen to some SSB signals tonight and I found a problem...

I cannot tune in the SSB signals, the mode control just spins around and has no effect.

This is the first time I have tried to listen to SSB so this is new to me.

Looking at the schematic before I open it up it looks like the mode switch should have a few positions to it and not just spin around.

Am I correct?

Thanks much,

Dave KC3AM

?

Hi Rob,

It is Network Sciences

Date Code (?) 7905

Thanks Lionel?

?

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

On Mar 21, 2023, at 4:17 PM, Dave via groups.io <kc3am@...> wrote:

Gary, Dave, John,

Thanks for the replies!

I removed the knob this afternoon and it is in good shape.
It looks like the set screw presses against a fiber like bushing that surrounds the shaft and this presses against the shaft for a tight fit.
It did not feel stuck but I cannot turn it by just grabbing the shaft with my fingers.
The shaft is round without a flat spot so I guess it is just a tight compression fit that does the work.
I can move the switch to all three positions with a pair of pliers and LSB/USB works just fine !!!

I may open it up and look at the underside and then try some lubricant of some sort on the shaft, any suggestions?
I have WD40 & PB Blaster here to loosen it up some to start but maybe some kind of light oil after that?

Dave KC3AM

On 3/20/2023 9:50 PM, Gary Follett wrote:

That knob ?should most certainly operate with a click at each position, allowing reception of AM, USB and LSB/CW.

There are two possibilities. One is simple, that the set screw for the knob is loose. I think this is a setscrew type knob…

If the set screw is very tight but you still cannot get a switch action, remove the knob and have a look at the shaft. Try to turn it gently with a pliers. If you get the same result, remove the cover and have a look at the coupling between the small inner shaft and the switch behind it to see if it is loose or broken. That coupling is below the chassis (underside) towards the back, with the shaft going between the coils of the bandpass filter coils.

Try that. If no joy, I have the last possibility you. Don’t want to hear unless you are really good at repair work.

Gary

W0DVN

On Mar 20, 2023, at 8:28 PM, Dave via groups.io <kc3am@...> wrote:

Hello everyone,

Last summer I picked up a 2-C to go with my 2-NT.
I have been using it for CW without any troubles.
I tried to listen to some SSB signals tonight and I found a problem...

I cannot tune in the SSB signals, the mode control just spins around and has no effect.

This is the first time I have tried to listen to SSB so this is new to me.

Looking at the schematic before I open it up it looks like the mode switch should have a few positions to it and not just spin around.

Am I correct?

Thanks much,

Dave KC3AM

That knob should most certainly operate with a click at each position, allowing reception of AM, USB and LSB/CW.

There are two possibilities. One is simple, that the set screw for the knob is loose. I think this is a setscrew type knob…

If the set screw is very tight but you still cannot get a switch action, remove the knob and have a look at the shaft. Try to turn it gently with a pliers. If you get the same result, remove the cover and have a look at the coupling between the small inner shaft and the switch behind it to see if it is loose or broken. That coupling is below the chassis (underside) towards the back, with the shaft going between the coils of the bandpass filter coils.

Try that. If no joy, I have the last possibility you. Don’t want to hear unless you are really good at repair work.

Gary

W0DVN

On Mar 20, 2023, at 8:28 PM, Dave via groups.io <kc3am@...> wrote:

Hello everyone,

Last summer I picked up a 2-C to go with my 2-NT.
I have been using it for CW without any troubles.
I tried to listen to some SSB signals tonight and I found a problem...

I cannot tune in the SSB signals, the mode control just spins around and has no effect.

This is the first time I have tried to listen to SSB so this is new to me.

Looking at the schematic before I open it up it looks like the mode switch should have a few positions to it and not just spin around.

Am I correct?

Thanks much,

Dave KC3AM

On Tuesday, March 21, 2023 at 02:15:29 PM MDT, Mark - WB0IQK <mgilger@...> wrote: