Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AHeck on January 17, 2022, 05:28:53 pm
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Thanks for taking the time to read this. I want to build a no frills +/- 40W with a pentode in V1 and enough headroom for large bar gigs with a loud band. So far I've got this. It was sounding good, I had it biased, but something must have happened because now I'm having problems getting a realistic reading on V5 Plate to OT CT. I've done a good bit of troubleshooting, switched tubes, both new tubes, completely rewired both tube sockets and back to OT, rewired bias circuit, triple checked all connections sturdy and correctly wired point to point, tested OT, tested tubes, rewired power section ground... Am I missing something or do these voltages tell you something I'm not seeing?
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Hi AHeck
Nice simple amp :icon_biggrin:
I noticed the Grid for V2A is coupled to Vol with a 0.22u Cap. Needs a DC path on Grid for correct Cathode Bias.
You could run the TC after V2, as V2 configuration has a low output impedance (Like a Bassman)
It would be of value to fit a pair of 1R 0.5W resistors in the V4 and V5 cathodes to check Output Tube Quiescent current.
I am not sure of the measurement "Plate to Output Transformer CT" (Its not something I do).
All the best with the amp.
Regards
Mirek
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Hi AHeck
Nice simple amp :icon_biggrin:
I noticed the Grid for V2A is coupled to Vol with a 0.22u Cap. Needs a DC path on Grid for correct Cathode Bias.
You could run the TC after V2, as V2 configuration has a low output impedance (Like a Bassman)
It would be of value to fit a pair of 1R 0.5W resistors in the V4 and V5 cathodes to check Output Tube Quiescent current.
I am not sure of the measurement "Plate to Output Transformer CT" (Its not something I do).
All the best with the amp.
Regards
Mirek
Thanks, Ill put in the 1Rs directly, slipped my mind. plate to OT CT voltage / plate to OT CT resistance for bias measurement.