1957 RCA 9-ES-6J Schematic Epiphany

[electra225]

What does R3 meadure?

[Hi-Fi-Mogul]

What does R3 measure?

Whoops, R3 270 K read 625 K, and I now replaced it.

Replacing it had no effect on the distortion.

Sorry this is dragging on, but it's a good review
for me.

[William]

No apologies needed, it's a learning session for all of us. At least I know it is for me.

Bill

[electra225]

What is the voltage now on pin 7 of the 12AV6?

[electra225]

And did you sub the 35W4? Did that raise B+ voltage?

[Hi-Fi-Mogul]

Pin 7 12AV6 now good at 58 V

I did sub another 35W4 tube, but I need to
take that reading.

[Hi-Fi-Mogul]

Okay, B+ off the 35W4 cathode is raised to 109 V.

[electra225]

The voltages seem better. How about the distortion? Still there?

[Hi-Fi-Mogul]

The voltages seem better. How about the distortion? Still there?

Yes, that dang distortion won't let go.

I also checked the OP transformer for primary
winding shorts per a friend's suggestion.
No shorts.

[electra225]

Do you have a method of injecting audio into the volume control? A transistor radio with an earphone jack works well. Maybe a tape deck or, better yet, a signal generator. I read where you subbed the cartridge with no change. I'd like to suggest injecting clean audio directly into the volume control. This test should tell us definitely whether the issue is what is fed to the amp, or how the amp is processing the signal. The old radio repair technique of "divide and conquer". That's about all I can suggest at this point. I'd say you have the basics covered.

[Hi-Fi-Mogul]

Do you have a method of injecting audio into the volume control? A transistor radio with an earphone jack works well. Maybe a tape deck or, better yet, a signal generator. I read where you subbed the cartridge with no change. I'd like to suggest injecting clean audio directly into the volume control. This test should tell us definitely whether the issue is what is fed to the amp, or how the amp is processing the signal. The old radio repair technique of "divide and conquer". That's about all I can suggest at this point. I'd say you have the basics covered.

Tomorrow I'll connect a CD player I have,
using alligator clip leads connected to an RCA cable.

Would you mind confirming which lugs
of the Vol pot I should connect the CD
positive and ground leads ?

And, I'll disconnect the phono cart input plug from
the amp chassis jack.

[electra225]

You want to connect the hot lead of the test oscillator (CD player) to where the cartridge was connected at the volume control. The center tap of the volume control feeds the amp. The third terminal will be grounded. You should protect the test oscillator with a .01 @ 630 volt, or similar, in the hot lead going to the amp. Then connect the other lead (neutral) to the amp chassis. You are working with a "hot chassis" record player amp. The cap in the hot lead will protect you and the device from high DC potential. If you have an isolation transformer, you should power up the record player amp on it to eliminate hum. If you get hum with the test oscillator, reverse the power plug to the record player amp. Make sure the test oscillator and the record player amp don't come into contact with each other. You can protect the common lead of the oscillator with a cap as well. I'd say that would be overkill, but you can sure do it and it won't hurt anything. If you have questions, just ask. I hope this makes sense.

Edit: I realize you may be getting sick of hearing from me, but I just thought of one more thing. Wiggle both audio tubes with the amp on. See if wiggling the tubes produces noise. If it does, you have a bad connection at the tube socket. Clean the tube pins and the tube sockets until there is no noise when you wiggle the tubes. Just for grins.....

[Hi-Fi-Mogul]

I am definitely not tired of your assistance, I'm always grateful
to learn.

I have copied and printed out your instructions for safely
using the CD player to test the RCA amp.

So, on the Beitman's schematic, I see Pin 2 of
J 1 to be the phono cart signal IN to Vol control.

That side of the Vol pot (lug 3) is where I would place
the signal/hot lead of the CD player.

I have a 0.01 mF 630 V cap to place in series
b/t CD player hot and lug 3 of Vol pot.

Other lead (ground) of CD player to chassis.

Before I do anything, I am curious about capacitor
C1. (0.06 mF)

There was no such capacitor in my chassis.
Lug 1 on J 1 was clean, no sign of removal of
anything.

Now, my chassis DID have a line to chassis 0.06 mF
cap.
It was connected from Lug 1 of J 2 to chassis.
I replaced that with an X1Y2 0.01 mF cap.

Question: Did the 0.06 mF cap C1 on Beitman
schematic perform as a line to chassis cap ?

Or would installing that cap make any
difference in the amp distortion ?

[Hi-Fi-Mogul]

The test was done, and no change in distortion
using the CD player as input.

I wonder if subbing a good 50C5 AA5 radio
OP transformer might be worth a try ?

I think that C1 is a B-/chassis
isolator cap, looking closely at the schematic.

[electra225]

I was also curious about C1. Why not sub a cap where C1 is supposed to be and see if it makes any difference. Is the distortion there immediately on power up, or does it take a few minutes to appear? The cathode of the 12AV6 is connected to common negative. C1 is from common negative to chassis. I don't see what it would hurt to sub that cap. Good luck.

[Hi-Fi-Mogul]

I put the 0.068 mF cap in, no improvement.

Well, I have a 4K ohm OP transformer.

Would it be worth subbing it out for a test ?

I know the 50C5 uses 2.5 K ohm load, but
maybe I'll know then if I have a bad OP
transformer.

Thanks !

[Hi-Fi-Mogul]

I realized the OP transformer I wanted to sub out,
was for PP amps. After reading about it I learned
it cannot be used for a single output tube amp.

[electra225]

If you have a little AA5 radio, you can use its output transformer without removing it from the radio. Hook it up with test leads. Leave the radio unplugged, of course. Just wire it like the original one is wired. You can even leave the original one in place. Use the speaker in the radio instead of in the record player. If the distortion goes away, then connect the record player speaker to make sure it's not the problem. Good luck.

What is the measured value of R2?

[Hi-Fi-Mogul]

Okay. Mystery solved.
Greg, I remembered you asked if the distortion
was immediate or delayed.

Well, last night I removed an OPT from a Steelman
3 tube junk chassis that used a 50C5.

Hooked it up today as you advised, and I thought it
sounded good for a few minutes.
Then muddy distortion after 7-8 minutes of play.

So, I turned it off, let the 50C5 (NOS) tube cool.
Put back a used 50C5, and the tube was the problem.

I guess even testing tubes, it's not the same as
putting them under a full load.

Then, I took off the Steelman OPT, and re-connected
the RCA one. Sounds just fine.

Thanks for the trek through the forest on this one.
My mind kept saying it has to be something simple
after almost all components were replaced.

[electra225]

Great job! Good to hear you found the problem. You kept at it and followed diagnostic procedures. You found components that were out of tolerance. Although they were not the cause of concern, you always do the right thing when you replace any known out of tolerance components. That thing will run dependably for years. Had you only fixed "what was broke" something else may have caused trouble in a short time, and all that work would be to do again. This forum is specifically for projects like yours. I thoroughly enjoyed participating in your project, and thank you for sharing it. I'll assure you, I had as much fun with your project as you did.