Silvertone 1333 tube amp

[frankeg]

I have a 1956 Silvertone model 1333 to re-cap and I found 2 pots wired as variable resistors between the plates of the 6SC7 & 6SN7GT preamp tubes and their power supply source voltage. The schematic I have shows normal resistors there. Could this be someones mod?

[galaxiex]

I would say that's a mod.
Someone trying to tweak something, or didn't have the correct resistors on hand.

[olddawg]

Those pots are not from 1956....

[Enzo]

Most pots have a date code on them.

[frankeg]

Thanks guys. The only thing these pots would tweek is the two preamp tubes plate voltage. I haven't worked with 6SC7 or 6SN7GT tubes but I'm guessing he was playing with their bias for whatever sound he wanted. It still seems a onnce and done thing since you have to take out the chassis to tweek.

[frankeg]

Here's the schematic

Here is the schematic. The pots are wired to pin 5 of each preamp tube.

[g1]

I'd think someone was tweaking the plate voltage (while disregarding the bias, which seems common ) as you mentioned.
If the pots are rated 1/2W or better, I suppose you could leave them as is.
Out of curiosity, how far off are the set values from the stock values shown on schematic?

[frankeg]

You are correct they are CTS pots made in 76 & 77.

[Chuck H]

The only thing these pots would tweek is the two preamp tubes plate voltage.

Well, no. They also change the plate load and that changes everything. Gain, current, bias, impedance AND voltage. With a pot as a plate load, and no other circuit parameters considered, it would be very easy to dial in an operational circumstance that is clearly undesirable (at best) or even dangerous (at worst).

[frankeg]

I'm taking it back to stock. I don't care for his soldering either. He told my friend that he's had it since the 60's and it's completely stock. That doesn't jive with CTS pots from 76 & 77. I'll let you know the values once I desolder which will be a week or so when the new parts arrive. The more I see of these old amps the more I liken them to a box of chocolates, you never know what you're gonna get...

[frankeg]

Well, no. They also change the plate load and that changes everything. Gain, current, bias, impedance AND voltage. With a pot as a plate load, and no other circuit parameters considered, it would be very easy to dial in an operational circumstance that is clearly undesirable (at best) or even dangerous (at worst).

Hi Chuck! Hope all is well. You always have the right words to expand and clarify what I'm trying to say and yes I totally agree with you! Thanks

[mozz]

Those pots are out of a color tv set.

[frankeg]

Those pots are out of a color tv set.

Hence the blue and red colors right? Makes sense. Thanks for the insight!

[Chuck H]

Hence the blue and red colors right? Makes sense. Thanks for the insight!

Oh I gave it a right away because I remember seeing these pots in TV's. I've never serviced them, but I took a few apart It didn't click before mozz mentioned it and then I got a little kick out of it. Fun.

[g1]

You are correct they are CTS pots made in 76 & 77.

Well I think Sears stopped branding TV's with the Silvertone name around 73. So I guess my hopes that they might still be official 'Silvertone' parts are dashed.