Hello all, I am doing some tweaking on a new build which started as a stock rebuild of a 50s PA. It sounds killer with my guitar, but this is supposed to be a harmonica amp, and I am having issues getting it tweaked for harmonica. The circuit is supposed to be a grail tone for harp players, but I am getting feedback at volume 1. I have tried a few things to get some more range, and I can now get the volume control up to 2.. I am looking for some feedback to help me get this to be more harp friendly.. I built the circuit stock, but fully removed the phono input. Here are things I have tried already: 1 - Lowered R6 to approx 82K 2 - added a 470k resistor where the phono volume control would have been 3 - added a 2.7M and 75K resistor at the input All the voltages are spot on, and the bias is 80% with old tung sol 5881, and 100.5% with plain old 6l6 (19W) tubes I have read that switching to cathode bias may help lower the preamp gain, but I am worried it will mess with the mojo of the amp.