Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on March 07, 2023, 02:52:28 pm
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Using a bucking transformer to get the proper dissipation (I know I can just raise the K bias R), in BF Vibro Champ. I'm lowering the screens rather than the raising the cathode biasing resistor, as per HBP, he suggested in another post here and elsewhere, to get proper dissipation. I'm there with dissipation at 12 watts, class A at idle by setting the bucking transformer at 14 volts less than wall current which is 123vac, gives me 108vac. to amp.
108 vac gives me 6.1vac at filaments and 4.9 on the 5Y3. is the lower Vac on filaments going to damage the tubes over the long haul?
HBP suggests rather than raising the the cathode R to get the correct dissipation it's better to drop the screen node in the Vibro Champ from 1K to 10K, and next node to 22K to get schematic preamp voltages and not touch the 470 ohm biasing R. Doing this gives me a difference of 55v from plate to screen on the 6V6, thus giving the correct dissipation without touching the Cathode R. There is a video posted here not too far back, a page or so about this. I do find that the distortion is much better sounding, not as harsh with the screen about 50/60 dcv less than the plate.
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108 vac gives me 6.1vac at filaments and 4.9 on the 5Y3. is the lower Vac on filaments going to damage the tubes over the long haul?
no
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... I'm there with dissipation at 12 watts, class A at idle by setting the bucking transformer at 14 volts less than wall current which is 123vac, gives me 108vac. ... I do find that the distortion is much better sounding, not as harsh with the screen about 50/60 dcv less than the plate.
Glad to hear it's working out!
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... I'm there with dissipation at 12 watts, class A at idle by setting the bucking transformer at 14 volts less than wall current which is 123vac, gives me 108vac. ... I do find that the distortion is much better sounding, not as harsh with the screen about 50/60 dcv less than the plate.
Glad to hear it's working out!
Thanks for all your help,HBP. Champ sounds great, on the verge of break-up dial at 5, plenty loud to jam in a room with a player or two.