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I finally finished my first amp build, a tweed princeton (5f2a) with a switch to lift the tone control. Everything seems to be working except when either the volume or tone knob hits 2 o'clock I get a loud screech and static sound. I tought it might be caused by the lift switch being grounded to a bus and not the back of the pot, and that might be causing some kind of ground loop. Might be obvious that I dont fully grasp the concept of a ground loop yet . well I changed that and I'm still getting that noise. Any ideas? Thanks in advance for any help

-Nate

P.S. I used 2 1n4007's insted of the 5y3.

You could try re-wiring all your circuit-grounds so that they form what's called a Star-Grounding System, basically each ground for each gain-stage gets returned to only one point on the Amp chassis, I'm thinking that the screeching-noise you're getting is in fact caused by the Amp going into self-oscillation, which the Star-Grounding System should cure, also make sure that the amp's HT has a suitably rated Electrolytic Cap or two going to ground to bypass any noise on the HT to ground....

If you're unsure what a Star-Grounding System is, you could try googling it....


Using 1N4007 Silicon Power Rectifier Diodes instead of a 5Y3 Rectifier Tube shouldn't cause any trouble, your amp's HT supply should be a bit stiffer and not sag as much, that's all....

Thanks Doc I'll give that a try and report back to the thred if that dosent fix it

Fixed. Tiny bit oscillation when maxed out, but no one ever said that was a bad thing

nat-han wrote:Fixed. Tiny bit oscillation when maxed out, but no one ever said that was a bad thing

You might be able to cure that by putting some small-value caps on the control grids of the power tubes to circuit ground, also, try putting a 100nF/630V cap in parallel with any HT bypass caps....