Hey Marcus, thanks for your help!norburybrook wrote:you have Hum? do your heaters have a center tap, if not have you got a pair of 100r registers to ground at some point from the heater wiring?
Chek the tightness of your speaker output jacks if they're grounging through the chassis, or put a groung wire to a ground point close by.
That's about as far as my knowlewge can help in this Fred I'm afraid. Dont be dissheartened though as this kind of trouble shooting is where I really learned about amp building, it can be frustrating but in the end for me it was really the part of the process where I really learned about things and made progress. If all my builds had worked first time I'd still be painting(building) by numbers [emoji1]
Marcus
I did not put 100R resistor on the heaters. I was re-reading Merlin blencowe’s chapter on hum cancelling on he advised the exact same thing or even better: a “humdinger” (500ohms pot wired on both heaters with wiper to ground.
My jacks output (as well as all the knobs and jacks plugs all share a ground bus on the back pannel. Forging on your experience I though I would try to leave no room for that possibility.
I retried the amp tonight and with humbuckers I have to push it a lot to get the hum (all knobs on 10 basically...). So I might tackle that issue but not as priority no1 [emoji6]
Mid boost works only on one side, signal is off on the other side.
Will try to get the power amp stage working 100% and then move back up the chain.
Is it normal to get huge cracks on the speaker when probing the power tubes?
Seems like I would have the amp running at 100% even if the volume knob are shut off!
I should have more time tomorrow to debug some more.
Humble and Dumble,
Fred.