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I was doing some experimenting with my Beltone AP-12. I used the Fender Champ 5E1 schematic as reference (both schematics attached). I first tried adding negative feedback with a 22K resistor, per the Champ. I really couldn't hear much of a difference at all.
I then bypassed the cathode resistor on the 6AQ5 power tube with a 25uF cap. Big difference in gain there (and likely frequency response). But moving the bypass cap over to the 6AV6 preamp tube (the one fed by the tone and volume controls) didn't sound any different to my ears than the power tube cathode resistor bypassed. Having said that, I did not do an A/B under typical playing conditions, just briefly with the chassis on the bench and through my test speaker.
So, I'm just wondering if anybody can suggest different values for the NFB resistor of bypass cap or weigh in on why bypassing the cathode resistor on the preamp tube might be better than that on the power tube, or vice versa, based on the existing design. Thanks!
B.
champ_5e1_schem.pdf
I then bypassed the cathode resistor on the 6AQ5 power tube with a 25uF cap. Big difference in gain there (and likely frequency response). But moving the bypass cap over to the 6AV6 preamp tube (the one fed by the tone and volume controls) didn't sound any different to my ears than the power tube cathode resistor bypassed. Having said that, I did not do an A/B under typical playing conditions, just briefly with the chassis on the bench and through my test speaker.
So, I'm just wondering if anybody can suggest different values for the NFB resistor of bypass cap or weigh in on why bypassing the cathode resistor on the preamp tube might be better than that on the power tube, or vice versa, based on the existing design. Thanks!
B.
champ_5e1_schem.pdf