Studio Pre Tube stages/schematics? Need help for a tube swap

[Thrashman]

So Ive been searching for a layout of the tubes in the studio pre, to see what tube does what, and where it sits in the preamp..

Just wondering if anyone can help me.

The issue for that matter is feedback without any guitar plugged in if the drummer jams a little, if the pre's volume is at 7, and lead gain is at almost 4, or higher.

Microphonic tube that is, or tubeS?

Help out!

 

[elvis]

The schematic is available on the web. V1 is by the input, running in order to V4 on the other side. V5 (reverb driver) is off by itself toward the back.

Could be a tube - you can tap each one lightly with a pencil eraser to see if one (or more) are very sensitive. Note that they will all make noise when you tap, but one may be a lot more sensitive than the others. Could also be a microphionic capacitor (one of the 25uF cathode bypass caps, for example).

Could be your power amp as well (assuming it's also tubes).

 

[Thrashman]

thanks.

Yes, but what does v1, v2, v3, and v4 do?? This is unknown to me

- Chris

 

[elvis]

The signal goes:

V1A (input buffer, gain)
tone circuit
V1B (tone circuit buffer, gain)
If LEAD is selected, then V3A and V3B, which gain and compress the heck out of the signal
If RHYTHM selected, V3 is bypassed
Both modes go thru V2A (gain stage)
Lead master and master controls
signal splits into reverb circuit and V2B (gain stage)
V2B runs to EQ (all solid-state), then to FX send/returns
FX return splits into channels A and B, with V4A and V4B as buffer/gain to record and main outputs

Reverb circuit is V5B driving tank and V5A buffering return. Reverb signal is mixed back in at input of V2B.