AC filiments with one side grounded

[Guitarist]

I now have two amps here with this arrangement. The heater wires aren't normally balanced but one side is soldered to the chassis. One amp, a Grundig, hums (though DC converted now) and the other I simply upgraded to a 3 prong cord and it's now dead-quiet. This AM equipped stereo amp sounds really sweet too. It actually had the input ground/shields ungrounded, meaning only grounded at the original source. I strung a ground to V1.
Perhaps I should return the Grundig to stock? I didn't know 1/2 of 6.3 V AC could be grounded like this.

[Robert M. Martinelli]

Hi,
If the thing hums even with DC powered heaters ( assuming the heaters supply is properly filtered and no ripple is present there ) then the hum is coming from somewhere else.... Is the output stage a SE or a PP one ? ( as you might already know the latter is a hum-canceling design, so, a humming P-P is a symptom of some imbalance ) - I'd also check the +B supply for proper filtering and low ripple - if everything tests OK there's still the chance one of the tubes is defective, so some tube swapping could reveal the culprit. If all of the above yields no results, then I'd say some hum enters the signal path by unwanted coupling, so you might want to check lead dress and/or use shielded wire where needed.

JM2CW

Hope this helps

Best regards

Bob

[Guitarist]

OK thanks, I'll have another look. I seems one-side grounded 6.3 volts AC works amazing in practice.