From tremolu–(at)–ol.com Sat Aug 22 00:59:57 CDT 1998
Article: 122708 of alt.guitar.amps
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: alt.guitar.amps
Subject: Re: Brown Fenders
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Date: 20 Aug 1998 22:34:19 GMT
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>>Anybody spend much time with the brown pitch-vibrato amps?
>I’ve found I can’t increase the value of the p/i input cap (.001) without
>getting the awful “beating” when the vibrato is in use.
>I’d like to thicken up the tone a bit. Already subbed .022 tone caps and
>biased
>my NOS 6L6’s to 35mA per tube.
>Any suggestions?
>
>Matt D
>

I’ve spent some time with those circuits. the small cap at the PI input is
used to kill the subsonic artifact signal coming from the 12AX7 that does the
actual modulation in the circuit. It functions as a single pole high-pass
filter in conjunction with the PI’s input impedance. There’s nothing you can
do to eliminate it entirely. You can minimize it by hand selecting the 12AX7.
Just try different ones, and one will have less of the beating than the others.