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This happens mostly in Head builds.

When you test the amp, make sure it doesn’t feedback and squeal when Gain , Fat and PAB are pulled, Vol is on max. and guitar plugged in. If it does, it is probably the wire dressing around V1. Particularly in a Head format build.

Pushing the wire connected to pin 6 towards pin 2 and 3 will induce squeal. When the wires almost touch, the squealing starts. Pulling the pin 6 wire as far from pins 2 & 3 wires as possible eliminated the squealing. Shorten these wires and secure them so they won't move around during transit and end up moving and repeating the squeal conditions.

If you need to stop any remaining squealing. Put a .001uF - .0015uF poly cap (Mallory 150) between grid pin 2 to the ground lug of the terminal strip.
At maximum volume & power, the squeal should be gone.

- from a collaboration of various members

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Stephen
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