Champ 5e1 sounds like an analog synth...WTF?!

[wcrankshaw]

I just replaced a prototype chassis on the first amp I built, a 5E1. After I got everything wired up seemingly correct, there is a very bizarre problem. When it's first turned on, everything is normal until the volume gets to around 3 or so. At that point it begins outputting a high frequency that drops down lower and lower until nothing as you turn up the volume. It sounds almost exactly like a tone generator on an old synthesizer. What in the world did I do wrong?

UPDATE: When the 12AX7 comes out the tone goes away. when the 12AX7 is plugged back in, the tone comes back starting low, and building up to wherever it was before the tube came out.

[wcrankshaw]

another update: I've got a ground buss taking the circuit board grounds to the chassis. I noticed that if I pressed on it, hum was less, so a bad ground connection. When it was loose the noise from the speakers was less like a synthesizer and more like really loud hum with a pitch. It's when the ground is fully tightened to the chassis that I get the sawtooth wave tone.

[Gtr_tech]

Thats called oscillation...caused by improper lead dress or layout errors.