Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: matt mincer on September 01, 2018, 01:46:52 pm
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Hey All,
I've had this on my bench for a while and think I made a breakthrough. If I understand correctly, Infinium is an auto bias circuit. It was keeping the neg bias at -65V constantly. As a result, no plate dissipation and no output. I put a 10k pot with a 27k resistor on the ground side in the path of the bias voltage. I can now get the bias around -39V which gives me about 21 watts per tube. Unfortunately, Bugera wouldn't provide a schematic so this was the solution I came up with. Can anyone think of a reason this wouldn't work long-term? The amp belongs to the Local School of Rock so I don't want to give it back if there are any potential issues. Thoughts? I can draw the circuit I "designed" if that would help.
Thanks
Matt
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There is already a bias adj in there somewhere. Might be OK now...but the next guy that looks at it will be confused. I have a high quality schematic in pfd for you but its too large to attach. Can I email it to you?Jim
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Hey All,
I took some pix of the amp. The top link is to the Infinum board. I'm told it's an auto bias circuit but it's not working in this amp. The 2nd link is to the mod I made so I could manually adjust the bias. It should have a linear taper pot but all I had was audio and it seems to work. The 3rd link is to all of the pictures I took.
Thanks
Matt
https://flic.kr/p/2aFSwqk
https://flic.kr/p/NyjTZd
https://flic.kr/s/aHsmrjhgVw