OK. My LAST question about SR mods!

[KeithC]

This one is in Gerald Webers book.
It is listed as "Improve Fidelity and Gain of One Channel" by eliminating series resistance on the phase inverter.

Basically is bypassing the 220k resistor and hooking up directly to the cap.

First what does "improved fidelity" and "series resistance" really mean as far as how the amp will sound?

I know in the end I would just have to try it but thought someone might have experience with it and could pass along some insight.

Any thoughts would be appreciated! :AOK

[ChrisGS]

I tried some of that stuff on my SR , and I put it back to stock. I think that those mods tend to make the pick attack more aggresive,and punchy. For me it seems to undo some of the sweetness of the Super Reverb clean sound, which I think is something that the SR does better than the other Blackface amps.

[KeithC]

I know I felt that way about disconnecting the negative feedback. I tried it that way for a while but put it back.

The easy things to change like removing V1 or putting a 12AX7 in the PI make a little difference.

If I get some feedback o this particular mod I may try it.

Thanks!

[hasserl]

The 220k resistor is there to prevent the signal from either channel bleeding back into the other. If you bypass the resistor you eliminate that function.

As for the nfb, try using a pot in series with the resistor rather than disconnecting it completely. As you've found out, some nfb is helpful. Try 5k for a value, that's what I've got and I like it.

[KeithC]

Originally Posted by hasserl

The 220k resistor is there to prevent the signal from either channel bleeding back into the other. If you bypass the resistor you eliminate that function.

As for the nfb, try using a pot in series with the resistor rather than disconnecting it completely. As you've found out, some nfb is helpful. Try 5k for a value, that's what I've got and I like it.

Thanks for the info.

From the mod in the book it would disconnect the Normal channel if you do it so channel bleeding wouldn't be a problem.

But, according to GW it increases "fidelity" and gain.
It must be somewhat different than just pulling V1 in that you do bypass the that 220k resistor. The mod then says to disconnect the other wire on the other 220k resistor that would be for the normal channel and tape it off to insulate it.

[tele_player]

Pulling V1 has a different effect - it increases the gain of the Vibrato channel by changing the bias on V2b.

[phsyconoodler]

Or simply separate the cathodes that share the same resistor and cap on V1 and V2.

[darkbluemurder]

Originally Posted by KeithC

This one is in Gerald Webers book.
It is listed as "Improve Fidelity and Gain of One Channel" by eliminating series resistance on the phase inverter.

Basically is bypassing the 220k resistor and hooking up directly to the cap.

First what does "improved fidelity" and "series resistance" really mean as far as how the amp will sound?

I know in the end I would just have to try it but thought someone might have experience with it and could pass along some insight.

Any thoughts would be appreciated! :AOK

Series resistance decreases high frequency response in connection with the miller capacitance in a tube. Since the 220k resistor goes to the phase inverter input cap I am not sure whether the miller capacitance of the PI tube can have any effect. Plus, the 12AT7's capacitance is lower than that of a 12 AX7. To make a long story short I would not bother to change it. A bad side effect would be that the channel isolation would no longer work.