I'm having a problem with the power supply/amp section of my 612v3, 1946 RCA victrola. The amp tubes (6f6g)are being cooked by 650 to 700 volts on pin 3 where the voltage should be (according to the RCA original and sams photofact) 375 volts. The full wave rectifier is pumping out 720 volts into pin 8 when it should be 420VAC according to the sams schematic. All volts are there no matter what mode (AM,FM, SW, etc.) Make a long story short, everythings being cooked downstream of the rectifier. The power and speaker transformers ring out and all new power caps. I'm thinking maybe the amps (6F6G's).
Any hints

Regards
Steve

:I'm having a problem with the power supply/amp section of my 612v3, 1946 RCA victrola. The amp tubes (6f6g)are being cooked by 650 to 700 volts on pin 3 where the voltage should be (according to the RCA original and sams photofact) 375 volts. The full wave rectifier is pumping out 720 volts into pin 8 when it should be 420VAC according to the sams schematic. All volts are there no matter what mode (AM,FM, SW, etc.) Make a long story short, everythings being cooked downstream of the rectifier. The power and speaker transformers ring out and all new power caps. I'm thinking maybe the amps (6F6G's).
:Any hints
:
:Regards
Steve

Hoo, boy, this is one big old radio. I need to peruse the schematics a while to get a feeling about this guy. I don't see, right off hand, hows the 6F6s could be causing this problem. I'll get back with you later, after I have studied the schematic a while.
Lewis

::I'm having a problem with the power supply/amp section of my 612v3, 1946 RCA victrola. The amp tubes (6f6g)are being cooked by 650 to 700 volts on pin 3 where the voltage should be (according to the RCA original and sams photofact) 375 volts. The full wave rectifier is pumping out 720 volts into pin 8 when it should be 420VAC according to the sams schematic. All volts are there no matter what mode (AM,FM, SW, etc.) Make a long story short, everythings being cooked downstream of the rectifier. The power and speaker transformers ring out and all new power caps. I'm thinking maybe the amps (6F6G's).
::Any hints
::
::Regards
:Steve
:
:
:Hoo, boy, this is one big old radio. I need to peruse the schematics a while to get a feeling about this guy. I don't see, right off hand, hows the 6F6s could be causing this problem. I'll get back with you later, after I have studied the schematic a while.
:Lewis
:
:
:
:

:::I'm having a problem with the power supply/amp section of my 612v3, 1946 RCA victrola. The amp tubes (6f6g)are being cooked by 650 to 700 volts on pin 3 where the voltage should be (according to the RCA original and sams photofact) 375 volts. The full wave rectifier is pumping out 720 volts into pin 8 when it should be 420VAC according to the sams schematic. All volts are there no matter what mode (AM,FM, SW, etc.) Make a long story short, everythings being cooked downstream of the rectifier. The power and speaker transformers ring out and all new power caps. I'm thinking maybe the amps (6F6G's).
:::Any hints
:::
:::Regards
::Steve
::
::
::Hoo, boy, this is one big old radio. I need to peruse the schematics a while to get a feeling about this guy. I don't see, right off hand, hows the 6F6s could be causing this problem. I'll get back with you later, after I have studied the schematic a while.
::Lewis
::
::
::
::Lewis
Thanks for replying so soon. Just a follow up, the main transformer is supposed to pump out 720VAC outta pins2 and 6. However, its like, as I stated earlier, theres no rectification of the + wave only but the whole + and - wave. My B+ voltage off of pin 8 of 5U4G is +370VDC, again just as it should be.

Regards
Steve

Did you do anything with the power transformer or rectifier wiring???? If you confused the three high voltage wires, you could easily have 700 volts instead of 350 at your rectifier cathode. Here's how: You're supposed to connect the two ends of the winding to the rectifier plates. The center tap goes to B-. However, if you connected one end to one plate, the center tap to the other plate, and the other end to B-, you'd get 700 volts. If you were to look at the cathode output from the rectifier on a scope, you'd see that every other wave was 700 volts and every other wave was 350 volts. When that passes through the filter system of your radio, it's a bit better than half wave rectification (350 volts is better than 0 volts), so it probably gets filtered quite well. The output should be something around 700 volts DC, and rather smooth. You may notice some excessive hum, but not too much.

Definitely check out the power transformer. Disconnect all three high voltage wires. Power up the transformer and carefully meter across two of them at a time. The two that give the highest reading are the two that should go to the rectifier plates. The remaining wire should give a reading half of what you saw with the other two wires when measured to either one of them (not both at the same time...don't do that or you'll fry the transformer). That remaining wire should be connected to B- according to the schematic. Also, the voltage between each of the other wires and this last remaining wire should be pretty much the same for both of the other wires. Significant difference may indicate transformer problems.

T.

Hi

Agree with Thomas. That's the only way you can have that high of voltage. The other thing may be your meter? Either reading wrong or on AC rather than DC?

Don't operate a radio if voltage is that high. It's way above rating of electrolytic caps. They will get hot and explode with excessive voltage.

6F6's will get hot but plates & screen shouldn't be red.

Norm

:Did you do anything with the power transformer or rectifier wiring???? If you confused the three high voltage wires, you could easily have 700 volts instead of 350 at your rectifier cathode. Here's how: You're supposed to connect the two ends of the winding to the rectifier plates. The center tap goes to B-. However, if you connected one end to one plate, the center tap to the other plate, and the other end to B-, you'd get 700 volts. If you were to look at the cathode output from the rectifier on a scope, you'd see that every other wave was 700 volts and every other wave was 350 volts. When that passes through the filter system of your radio, it's a bit better than half wave rectification (350 volts is better than 0 volts), so it probably gets filtered quite well. The output should be something around 700 volts DC, and rather smooth. You may notice some excessive hum, but not too much.
:
:Definitely check out the power transformer. Disconnect all three high voltage wires. Power up the transformer and carefully meter across two of them at a time. The two that give the highest reading are the two that should go to the rectifier plates. The remaining wire should give a reading half of what you saw with the other two wires when measured to either one of them (not both at the same time...don't do that or you'll fry the transformer). That remaining wire should be connected to B- according to the schematic. Also, the voltage between each of the other wires and this last remaining wire should be pretty much the same for both of the other wires. Significant difference may indicate transformer problems.
:
:T.

:Did you do anything with the power transformer or rectifier wiring???? If you confused the three high voltage wires, you could easily have 700 volts instead of 350 at your rectifier cathode. Here's how: You're supposed to connect the two ends of the winding to the rectifier plates. The center tap goes to B-. However, if you connected one end to one plate, the center tap to the other plate, and the other end to B-, you'd get 700 volts. If you were to look at the cathode output from the rectifier on a scope, you'd see that every other wave was 700 volts and every other wave was 350 volts. When that passes through the filter system of your radio, it's a bit better than half wave rectification (350 volts is better than 0 volts), so it probably gets filtered quite well. The output should be something around 700 volts DC, and rather smooth. You may notice some excessive hum, but not too much.
:
:Definitely check out the power transformer. Disconnect all three high voltage wires. Power up the transformer and carefully meter across two of them at a time. The two that give the highest reading are the two that should go to the rectifier plates. The remaining wire should give a reading half of what you saw with the other two wires when measured to either one of them (not both at the same time...don't do that or you'll fry the transformer). That remaining wire should be connected to B- according to the schematic. Also, the voltage between each of the other wires and this last remaining wire should be pretty much the same for both of the other wires. Significant difference may indicate transformer problems.
:
:T.

Think I found it, the bleeder resistor R1B in parallel w/ C2 (16 mf cap) burned up. It's a big mother, 2520, 4W rating.
Heres hoping.
By the way, thanks for the transformer suggestion, it led me back to the resistor. I had to replace the 180 earlier on.
Regards
Steve

Interesting. I see how voltages could get out of control, but I'm not sure how they could go up to 700. I assume that they are fine now? Did you replace the resistor? .....Please do check the transformer thoroughly. The resistor could have burned up due to a mis-wire of the transformer. If you replace the resistor and the transformer is mis-wired, you could both burn up your new resistor and burn up the transformer.

T.

:Interesting. I see how voltages could get out of control, but I'm not sure how they could go up to 700. I assume that they are fine now? Did you replace the resistor? .....Please do check the transformer thoroughly. The resistor could have burned up due to a mis-wire of the transformer. If you replace the resistor and the transformer is mis-wired, you could both burn up your new resistor and burn up the transformer.
:
:T. Tom,
Absolutely, the first thing I did was remove the rectifier tube and ring out and check voltages and pin connections. Good call, but alas, all was hooked up right and the xfmr is pumping out all the correct voltages. The plate volts are correct according to the part description in sams photofact list. The center tap volts are are about 15 volts high. (-40 as opposed to -25 as it should be). I can almost see the power supply in my sleep, I've been over it so many times. Check me on this one, the only way to get a xfmr voltage to drop is to load it down with some circuit. Sams says that pin 4 and 6 on the full wave rectifier should be 420VAC and I continue to read the 700VAC. The unly thing comes to mind is a full AC wave at these pins. I have no o'scope to verify. Am I barking up the wrong tree???

Regards and Happy New Year
Steve

Sams says that pin 4 and 6 on the full wave rectifier should be 420VAC and I continue to read the 700VAC. The unly thing comes to mind is a full AC wave at these pins. I have no o'scope to verify. Am I barking up the wrong tree???
:
:Regards and Happy New Year
:Steve

Pins 4 or 6 may read close to or around 400 -420 vAC but that is if you reference it FROM the CT.

Across the whole winding (from pin 4 to pin 6) you will read 700vAV

But everything is referenced from the CT.
So you should also measure the DC voltage from the chassis or CT as a reference also.

Measuring DC referenced from the Chassis or CT you should measure about 370-400VDC at the input of the field coil and about 270-290vDC on the other side of the field coil.