Silvertone 1484 Owners Please Confirm This Resistor Value.

[Guitarist1983]

V4 12AX7 Pin 2 is connected to 2 resistors: R40: 560K and R41: 68K. Mine is connected to a 560K and a 150K (Brn-Green-Yellow). Anyone else have a non-68K resistor for R41?
Follow-up question: Any resources for understanding the Silvertone's reverb circuit?

[The Dude]

Schematic?

[Guitarist1983]

[Enzo]

That is the reverb recovery circuit. I can't see that it would matter much. If you are concerned, slap another 150k in parallel to see it it changes the reverb. That would result in 75k, which is close enough for testing. Might increase the reverb signal a bit.

REverb? I don't know of any book analysis, but the ends are piezos. A piezo drives the spring and another is the pickup. The drive side is a push-pull stage comprising V5. The tiny square on the print is a piezo element.

On the pickup end, a piezo gathers the reverb signal and feeds it to your pin 2. That triode amplifies it and mixes it into V3 with the channels.

The reverb unit itself is utter crap. It has all the tone of a screen door spring. Sorry. It is one large spring. TRhe two piezo elements are stuck into little claamps that make electrical contact too. The piezoz stick up into the spring coils to make mechanical contact.

[Guitarist1983]

That is the reverb recovery circuit. I can't see that it would matter much. If you are concerned, slap another 150k in parallel to see it it changes the reverb. That would result in 75k, which is close enough for testing. Might increase the reverb signal a bit.

REverb? I don't know of any book analysis, but the ends are piezos. A piezo drives the spring and another is the pickup. The drive side is a push-pull stage comprising V5. The tiny square on the print is a piezo element.

On the pickup end, a piezo gathers the reverb signal and feeds it to your pin 2. That triode amplifies it and mixes it into V3 with the channels.

The reverb unit itself is utter crap. It has all the tone of a screen door spring. Sorry. It is one large spring. TRhe two piezo elements are stuck into little claamps that make electrical contact too. The piezoz stick up into the spring coils to make mechanical contact.

Thank you for the information. My 1484 was "serviced" by the previous owner(s)--new caps, 3-prong power cord, a few new resistors. I'm just walking my way through the amp looking for bugs. It sounds quite good, but there are a few quirks/issues I'm researching--a low-level buzz here, a hum there. Reverb works some days, other days it doesn't....

[Helmholtz]

V4 12AX7 Pin 2 is connected to 2 resistors: R40: 560K and R41: 68K. Mine is connected to a 560K and a 150K (Brn-Green-Yellow). Anyone else have a non-68K resistor for R41?
Follow-up question: Any resources for understanding the Silvertone's reverb circuit?

Higher value R41 increases rev recovery level.


The rev drive circuit is wired like a Paraphase PI. As the load (piezo transducer) is connected between the anti-phase outputs, this results in push-pull operation.
So the circuit can be described as a self-splitting class A push-pull stage.

The PP operation allows for large voltage swings, needed for the high impedance piezo

[Guitarist1983]

Higher value R41 increases rev recovery level.


The rev drive circuit is wired like a Paraphase PI. As the load (piezo transducer) is connected between the anti-phase outputs, this results in push-pull operation.
So the circuit can be described as a self-splitting class A push-pull stage.

The PP operation allows for large voltage swings, needed for the high impedance piezo

Thanks. Based on your summary of the rev drive circuit, I have a lot to learn--or perhaps I'll ignore the Silvertone Reverb circuit since I don't like its sound.