SF Twin Reverb - Vibrato Channel Breakup

[pdf64]

Brill, I bet that must be a relief
Bonus points? I'm enjoying the main prize too much to fully get my head around it, but yes, it seems weird
I initially thought you meant the 12k - 0.01uF on the pull boost, which as noted rolls the top end off a bit (FYI I thought it sounded better if both those and the bright cap on the master vol were removed).

But no, it's 220k - 0.01uF from the LTP plate.
Dunno, though it reminds me of the 220k feedback resistors on the power tubes of the AB165 Bassman http://schems.com/schematicheaven.ne...b165_schem.pdf
Perhaps the local feedback it adds helps to keep things under better control when the global loop loses control on being overdriven?
That would be consistent with the blocking distortion mitigating changes that were made; it may be something that's worth another look, being as the CBS engineers seem to know what they were doing.

The master vol does seem to mute the signal when set to min, so perhaps they tried it and thought 'why not'?

[nickb]

But no, it's 220k - 0.01uF from the LTP plate.
Dunno, though it reminds me of the 220k feedback resistors on the power tubes of the AB165 Bassman http://schems.com/schematicheaven.ne...b165_schem.pdf
Perhaps the local feedback it adds helps to keep things under better control when the global loop loses control on being overdriven?
That would be consistent with the blocking distortion mitigating changes that were made; it may be something that's worth another look, being as the CBS engineers seem to know what they were doing.

The master vol does seem to mute the signal when set to min, so perhaps they tried it and thought 'why not'?

I was thinking more about the fact that the MV lower end is returned to the 100 ohm feedback point.

When the MV is at min the feedback is applied equally to both V6A and V6B (inverting and non-inverting) inputs. Note the V6B input is referenced to the 100ohm feedback point also. When the MV is at max less feedback is applied to V6A so we have variable negative feedback control synced to the MV.

Seems they really wanted to get away from clean in this rev.