Hi, this is my first post. I am working on my YBA-1 and I am trying to lower my preamp voltages from stock. A bit closer to 1986/7 specs. The b+ rail is as it is in the stock schematic (with the exception of new 50uf caps and more screen protection) until v1 &2. To be clear, in the stock configuration there are no issues.
Changes I have made. 10k resistor right before the b+ goes to v2 pin 1 then an additional 15k right before the 100k plate resistors on v1. I have tied v1 cathodes to an 820R bypassed with a 220uf but this problem has occurred with all cathode resistor values I have tried. As soon as I bring the voltages back up all is fine. But I want to be able to brown it out a bit.
voltages:
- and about 437 on the plates of v4&5
My issue is I seem to be getting some nasty distortion (not the good kind) like v1 is out of bias. and if I turn up past 3 o'clock on the volumes it goes into microphonic feedback. I know that lowering the voltage on v1&2 is pretty common on these but I have never heard of anyone having to change plate resistors.
Any help would be appreciated thank you.