Two channel 5f2a Princeton

[glassesnvests]

I had just completed a 5f1 build, and everything was awesome and it sounded fantastic, but me being me, I decided I wanted to trick it out. I saw that the Supro 16t (gretsch 6151) had an interesting topology and wanted to see if I could incorporate the preamp to mate with the power amp of the princeton. I just added another dual triode and using a DPDT switch I made it to where the input was on the middle lug of one side, switching between the input grid of either the Princeton preamp or the Supro, and the other middle lug was connected to pin 5 of the 6V6 switching between the plates of V1b and V2b post-capacitor.


When in he different channels, the volume on the unused channel has to be all the way down or else I get a pretty intense oscillation, which can vary with frequency depending on the positions of the volume and tone knobs. Any ideas/experiences with this? If I could fix this oscillation, it's be a killer little amp. I'll sketch up a .sch when I can of what it looks like...
Thanks!
GnV

[AZJimC]

I'd try using the input side of the switch to ground the input that is unused? The oscillations are likely related to the unused preamp hanging in the air, with no ground reference. Other things may be to try a large value resistor to ground on each leg.