I'm somewhat familiar with tube amplifiers, but normally only use ones that are under 500 volts.
Trying to help a friend with an Oldchen 845-A amplifier, the only information about the trim pots in the owner's manual sates:
" ·This device has an internal resistor to adjust the value of the tube bias, there are two adjustments to the
midpoint of the 300B electron filament, you are not recommended to adjust by your own."
The amplifier is only a few months old and one 845 is bad, so a new matched pair is arriving soon.
Tubes used 6SN7 - 300B - 845
I don't have the amplifier on hand so a couple of pictures from purchase place is the only thing I can provide for clues.
Hum balance - I'm not too concerned about other than confirming the (near) blue pots for the 300B tubes are for hum balance?
The other (far) blue pots I assume are for hum balance on the 845 tubes, but can't see where they are in the circuit in these pictures.
Maybe they serve some other purpose???
Bias - The 2 large pots? - any clue on where to measure and what value?
Thanks for any help,
Lin
Trying to help a friend with an Oldchen 845-A amplifier, the only information about the trim pots in the owner's manual sates:
" ·This device has an internal resistor to adjust the value of the tube bias, there are two adjustments to the
midpoint of the 300B electron filament, you are not recommended to adjust by your own."
The amplifier is only a few months old and one 845 is bad, so a new matched pair is arriving soon.
Tubes used 6SN7 - 300B - 845
I don't have the amplifier on hand so a couple of pictures from purchase place is the only thing I can provide for clues.
Hum balance - I'm not too concerned about other than confirming the (near) blue pots for the 300B tubes are for hum balance?
The other (far) blue pots I assume are for hum balance on the 845 tubes, but can't see where they are in the circuit in these pictures.
Maybe they serve some other purpose???
Bias - The 2 large pots? - any clue on where to measure and what value?
Thanks for any help,
Lin
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It's difficult to say without a schematic but my guess would be the large pots are hum balance. The board has four small pots and without any details it's impossible to know what to measure or where.
Even though the amplifier was not purchased from them Hifi Exquis gave me the information needed.
The 4 blue multi-turn pots are for hum balance and the larger black pots are for bias using the blue resistors next to them.
The 4 blue multi-turn pots are for hum balance and the larger black pots are for bias using the blue resistors next to them.