About the Vibroverb: are the tapped treble pots necessary ?

4/16/2000 3:51 PM

EmScott

About the Vibroverb: are the tapped treble pots necessary ? The 6GL6 (or is it 6G16 [sixteen ?]) Vibroverb   tone controls used a 70K-tapped 250K audio taper   pot for the treble pot.     However, Doug Hoffman's AB763 circuit board (see   layout diagram at http://www.hoffmanamps.com/ab763.htm)   appears to use a Brownface-era tremolo, i.e.,   without an optoisolator like the BF/SF tremolos   used.     He told me once on the phone that it modulated the power tubes bias, like the brownface tremolo did.     However, there doesn't seem to be a   tapped pot (or a 68K resistor used as a "work-   around") anywhere near the treble pot on the   Hoffman diagram.     Does that mean that you can just use a   "regular", salt-of-the-earth 250KA pot in the   treble position? What about the connection at   the tap on the Fender diagram--can one just   IGNORE ?     I'm just not able to quite get it when I look   at the 6GL6 circuit diagram and the Hoffman   diagram--thanks in advance to anyone who can   help.