You probably need to adjust the hum balancing potentiometer or otherwise balance the heater grounding path. Is the hum about the same in both channels?
How much hum is there (from how far away can you hear it?) and what speakers are you using? 300B amps are not typically 100% hum free.
Unless something else is faulty, of course. Bad tubes, bad power supply capacitors, bad rectifier, the list goes on.
I wasn't referring to bias. Commonly 300B tubes are used in cathode bias circuits and bias isn't adjustable. But hum balance should be. Does it have adjustments?Since the 300B is a DSirect Heated Triode you best bet is to adjust the bias on the tube, like raindance said.
Thanks, no serviceable parts or adjustments available. Hum only heard from 12" away from speaker cone at 6/10 volume. Amp fairly new as are tubes. Rectifier appears fine, though is the weak part of the design. Tried other outlets with no success. Thank youYou probably need to adjust the hum balancing potentiometer or otherwise balance the heater grounding path. Is the hum about the same in both channels?
How much hum is there (from how far away can you hear it?) and what speakers are you using? 300B amps are not typically 100% hum free.
Unless something else is faulty, of course. Bad tubes, bad power supply capacitors, bad rectifier, the list goes on.
Who made the amp? Not everyone grounds things properly, and layout can also impact things negatively..
Is the hum a pure low tone or does it have some buzziness to it?
Audio Nirvana, yes there is definitely some buzziness to the hum.Who made the amp? Not everyone grounds things properly, and layout can also impact things negatively..
Is the hum a pure low tone or does it have some buzziness to it?
Audio Nirvana 300B thanksWhat amp is it? I've repaired many, but this is like flying blind.
Audio Nirvana, yes there is definitely some buzziness to the hum.
Sounds great actuallyI looked at a photo of the inside and it appears to use DC heaters, so no balancing issue. Maybe it just is the way it is. Does it sound OK?
Its for sure designed for the USYou should also make sure it's designed for the USA mains voltage (120 volts +) and not 110 volts. It may seem trivial, but 10% high on heater voltage is bad. 10% high on HT is very bad and can blow smoothing caps on switch on. It also causes a cathode bias amp to run too "hot" and can cause hum and premature tube failure.
Yes same both channels, actually sounds better with cheater plug om PCOK, that points more to grounding than transformer pickup. Same in both channels?
The actual transformers hum on start-up, then the hum source goes away after a few minutes. I will try switching out rectifier tomorrow to see if that makes a differenceAnd hum balance pots are possible with DC heaters, so there's that. There's a discussion at the asylum on this amp.