I built a 2 stages differential pp amp (uf86->el86, became later 6s3p-ev > 6p43p-e) with toroid output transformer.
If I touch with hand the (steel) cover of OPT, it start to hum in the speaker.
If I remove the cover and touch the OPT, it hums even higher.
First question: why?
Second question: what is the better, connect the cover at signal ground (0V) or connect it to safety ground (earth)?
Last one: Am I supposed to ground the screw fixation of toroid OPT? the plate is not made of steel, but wood.
For your information there is a Sowter 8920 at input used as phase splitter, so NO connection between signal ground and safety ground.
Thank you.
If I touch with hand the (steel) cover of OPT, it start to hum in the speaker.
If I remove the cover and touch the OPT, it hums even higher.
First question: why?
Second question: what is the better, connect the cover at signal ground (0V) or connect it to safety ground (earth)?
Last one: Am I supposed to ground the screw fixation of toroid OPT? the plate is not made of steel, but wood.
For your information there is a Sowter 8920 at input used as phase splitter, so NO connection between signal ground and safety ground.
Thank you.
Thank you.
OK, will do.
Yes, negative speaker binding post is at ground.
Do I need a LF generator or just shorted input and try to see something in HF range with the oscilloscope?
I would do safety earth, since the chassis is attached as well (usually!)
OK, will do.
... and one side of the secondary (output) is grounded?
Yes, negative speaker binding post is at ground.
High frequency parasitic oscillation?
Do I need a LF generator or just shorted input and try to see something in HF range with the oscilloscope?
Quote:
High frequency parasitic oscillation?
Neither LF generator nor shorted input, and your hum is not continuous, so scoping the output while not humming will show you nothing.Do I need a LF generator or just shorted input and try to see something in HF range with the oscilloscope?
So first attach scope probes to output terminals (because you hear hum, so it´s going to speakers) and then touch transformer both ways , with cover and straight to windings, exactly what you did before.
*When* you hear hum, you will see "something" on the screen.
Describe what you see and even better have somebody else (not you) take a scope screen picture, post it here.
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