Re: FWD: A100 with a hum

[bobs@hopf.dnai.com (Bob Schleicher)]

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>>From CousinGJ@aol.com  Thu Jan  4 00:50:16 1996
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>Subject: A100 with a hum
>
>     I recently purchased an A100. There is a small problem in the percussion
>circuit. I'm hoping someone can help. There is a low frequency hum that is
>always present (the pitch of the hum is the same as B1 played with the
>fundamental drawbar pulled). It completely disappears when percussion is
>utilized. 
>

Sounds like 120HZ ripple getting into the +205V power supply, which in turn
is divided to provide the +37 and +33 volt supplies for the percussion.  My
best guess would be an open filter cap.  Check them all.  An easy way is to
bridge each section with a known good cap, about 40MFD @ 450V.  (watch the
polarity)

This is not uncommon and is a cheap & easy fix.  Also make sure the 12AU7,
last tube on the right, dosen't have a heater to cathode short.

The Leslie kit installation is very straightforward and should present no
problems if you follow instructions.

Bob S.