• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Help me tame this Angela Super Single-Ended guitar amp? Oscillating + no headroom

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#22
The relation between supersonic oscillations and audio range sound is called "squeeging" by old Ham radio guys. The circuit oscillates at some VHF, driving active stages into cutoff, the oscillation stops, DC voltages relax, VHF oscillations resume, repeat at an audible rate.

Any film cap is fine for the Zobel, 100VDC rating is plenty. Might want a 2W 10R resistor since it's actually oscillating now. Use a 10K dropping resistor with your 16uF cap for first stage B+.

All good fortune,
Chris
 
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#23
yes, the FB resistor is out. I've rebuilt the thing 3 times today and I believe Kay was correct. Simplifying the grounding scheme and judicial application of wire ties and sticky squares seems to have done the trick, no more squealing. I also installed a 30uF/500v reservoir cap...is this too big for a 5Y3?

now, as to the high voltages. perhaps because the PT has a hv rating of 640v @ 173mA and I'm only using ~90mA, I am getting voltages on the plates and screens that are just too high for a 6V6. The RobRob calculator had me at 100% and the screen voltages were 360v, where the rating for a new JJ is 315v. While a larger K resistor would lower the current thru the tubes, it would raise the b+ and subsequently make the screen voltage even higher. Should I be adding resistors before the rectifier tube, or maybe swap to 5881s?

thanks

w
 
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