1957 RCA 9-ES-6J Schematic Epiphany

[Hi-Fi-Mogul]

I bought this little 3 tube RCA, because I had not had an RP-205
changer to work on for some time.

When I pulled the Sams and the Beitman's schematics,
they each had different tube complements.
Sams: 12SQ7, 35Z5, and 50L6.

Beitman's: 12AV6, 35W4, and 50C5.

I found a production change of the audio tube from a 12SQ7 to
a 12AV6, but that was the only tube mentioned being changed.

Sams had a line to chassis capacitor. Beitman's did not.

My chassis had the 12AV6 lineup (Beitmans), but also the
Sams line to chassis cap.

I finally realized that no matter which tube was in my
chassis, that I should look to how the circuit connected
to the discreet parts of the tube.

So, e.g. both schematics used the plate
of the output tube in the same design.
Then it was very simple to review the circuit.

Every now and then I this little boost in
observation and learning. It's great.

[electra225]

Mr. Mogul, you have either chassis RS 157 or RS-157B. Sams 351-15 shows one version with the octal tubes, 12SQ7, 35Z5, 50L6. Beitmans shows RS 157B with the miniature tubes, 35W4, 12AV6, 50C5. There is an update in Sams 365-1 that shows Production Change Bulletin 188-D. That's the one you need to shed some light on your question. I'm sorry, but I don't have that. Good luck.

[Hi-Fi-Mogul]

Mr. Mogul, you have either chassis RS 157 or RS-157B. Sams 351-15 shows one version with the octal tubes, 12SQ7, 35Z5, 50L6. Beitmans shows RS 157B with the miniature tubes, 35W4, 12AV6, 50C5. There is an update in Sams 365-1 that shows Production Change Bulletin 188-D. That's the one you need to shed some light on your question. I'm sorry, but I don't have that. Good luck.

Thanks Greg.
I have both schematics, and another forum's nice
member found the Bulletin 188-D.
It had one sentence saying the 12SQ7 was changed to the 12AV6.
And a diagram with a 5.6 Meg resistor as a change.
Very odd no mention of the rectifier and output tube changes.

I've got the caps together, and will try to saw off the
multi-value e-lytic can, so I can stuff the 2 new ones in it.

[electra225]

I believe we may both have seen the same information on another forum. I thought it might help you.

[electra225]

I believe we may both have seen the same information on another forum. I thought maybe it would help you.

[electra225]

I believe we may both have seen that information on another forum. I thought maybe it would help you.

[Hi-Fi-Mogul]

Recap is all done and I have sound.

There is some distortion at the 3/4 vol control point.

The original Sonotone 2-T is good. Speaker tested OK.

I checked the 12AV6, and it is in the Replace/Weak zone
on my Precision 10-12 tube tester.

A friend down the street says he has the tube for me.

Questions please:
Is the distortion likely due to the bad tube ?

And, if so, what component in this tube is failing ?

[electra225]

I've seen audio tubes that test bad that will still work fine. Subbing that tube would answer your question. You really haven't given enough information on the distortion. 3/4 volume is pretty loud. IT could be lots of things. A speaker with a rubbing voice coil, something vibrating in the cabinet, or something else in the amplifier. Voltage checks might be in order. What is the output of the rectifier? How about the other audio tubes? Did they test good? Have you subbed them to see if it makes any change? Did you check or change the cathode bypass components? What are the voltages on the audio output tubes? Good luck.

[Hi-Fi-Mogul]

Thanks for the reply, Greg.

For this, single 50C5 output tube amp,
3/4 on the Vol pot only gets the volume
to listenable level.

I checked the speaker, no rub.
Subbed another speaker to confirm.
Speaker is on work table out of cabinet.

I replaced the 50C5, known for issues,
with a tested NOS, no change.

35W4 rectifier tests OK.

Will run voltage checks tomorrow with the
new 12AV6 installed.

I know it's a rarity that a problem is actually
caused by a "bad tube", ha ha !

[electra225]

Can you describe the distortion? Could it be a needle or cartridge issue? Have you tried increasing/decreasing tone arm pressure to see if that makes any difference? Are the motor mounts nice and soft? If they or the drive tire are hard, that might transmit rumble to the cartridge, then to the amp at a certain volume level. I'd feel more comfortable giving better advice if I knew a little more about the distortion. Voltage checks at B+ (cathode of the rectifier) and at the plates and screens of the audio tubes would tell me more.

[electra225]

The "50C5 issue" is an old wives tale somebody started on ARF. Why, I have no idea. Maybe like the "don't plug it in until you spend thousands on it or you;ll burn your house down" and, more famously, the 6X5 rectifiers burning up Zenith power transformers. There were millions upon millions of small radios built using a 50C5 output tube. I'll bet in the 40 years I've been tinkering with radios, I haven't replaced two dozen 50C5's that I could prove were bad. They run hot, but I've found them no more trouble-prone than any other output tube. Occasionally, I'll find one with grid emissions or with gas, but that's about it. I have way more trouble with 6EU7's than I do the 50C5's.

[William]

Here's my two cents worth, something that happened to me. I went through the same thing awhile back. Everything seemed to test ok, but just did not sound right and the volume was off. My final solution was to change the cartridge and bingo all the problems were gone. I was really hoping that was not the case as the cartridge was a Shure ceramic. I have another unit with a Shure ceramic that is a real performer, it makes the unit. But, having a bad cartridge, not matter what brand, is not a good thing.

Bill

[electra225]

Bill, I read on another forum about a member who had an old cartridge that didn't sound "quite right". He put it under a microscope and found it filled with dirt and debris. He cleaned it, and put it back in. A good cleaning fixed his cartridge. Did you toss the Shure?

[Hi-Fi-Mogul]

Okay guys, here's more data.
(BTW, I still cannot load a pdf file, so I
made a .png of the schematic)

1. The new 12AV6 made no difference in the
distortion.
If I had to characterize it, I would say its most pronounced
in the lower frequencies of the songs.

2. Voltages measured with DMM

12AV6
Plate Pin 7: 48 V
Grid Pin 1: (-) 0.74 V
Cathode Pin 2 : 0 V

35W4
Plate Pin 5: 0.23 V
Cathode Pin 7 : 105 V

50C5
Plate Pin 7: 96 V
Grid Pin 2: 1.16 V
Cathode Pin 1: 10.4 V
Grid Pin 6: 90 V

[electra225]

The schematic says all voltages should be + or - 20% from those given, at 115 volts line voltage. If your line voltage is 115 volts, then the voltages are within tolerance. If it is higher than 115, they are a tad low. My suggestion would be to sub the rectifier if you have a new one. See if the voltages change. I really don't think they are that far off. The cathode voltage on the 50C5 is high, the rest are low. You might measure R6 to see if it has drifted. It should be real close to value, 150 ohms. Cathode voltage is still within the 20% tolerance.

We can't load pdf files on the forum. Only jpeg or png, something like that. That is a change to the 3.0 version of the forum software. Pdf files can be used, we just have to handle them differently, like in an Archive or similar, when that time comes...

[William]

Greg, I still have the Shure cartridge and I did try cleaning it but no difference.

Bill

[Hi-Fi-Mogul]

Thanks for the check out on those voltages.
I think my VAC is around 120 here, if I remember.

I do have several 35W4 tubes to try.

I will disconnect one side of R6 out of circuit and test it.

I did try another cartridge, with the same distortion.

But, I think things are getting close now for a solution.

No problem about the pdf files, easy enough to make an
image.

[electra225]

You might check C6 and R4 as well. I assume C6 was replaced. Make sure R4 hasn't drifted.

[Hi-Fi-Mogul]

You might check C6 and R4 as well. I assume C6 was replaced. Make sure R4 hasn't drifted.

C6 and all other caps replaced.

R4 (470K reads 500K ohms)

R6 (150 reads 200 ohms)

I have both values and will replace the old
ones.

R6 certainly is off, and I hope that will
rectify the problem.

[Hi-Fi-Mogul]

Ix-Nay on the new resistors solving the distortion.

I'm going to spray the audio tube pins w/deoxit and
put tube in/out of socket to clean it.
Then I'm going to re-flow the audio
tube pins' solder points.

Everything's been replaced, except R5, R9 & R3 resistors, which
check OK.

Now a bit perplexing....