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In Reply to: Instantaneous hum posted by breadhead on April 5, 2007 at 04:08:33:
but alas, as you can see below, everyone has their pet experiences
and thoeories. Here's what I'd do: Order a copy of 'Valve Amplifiers'
by Morgan Jones (former BBC engineer). Browse through EVERYTHING
pertaining to grounds and grounding, shielding, construction practices
transformer placement etc. It is very cleary written, and will help
you for a more complete understanding of the issues involved. Think
of it as an investment in your understanding and appreciation of
the craft.Remember: isolate and conquer. Amps are systems, chains of cause and
effect. Start at the output, and work your way back step by step,
until you find the problem.It is throwing darts in the dark to just conjecture what your prob-
lem is by long distance. You might end up trying everything before
you come to the solution to your hum, or you might do one little
thing --and presto. Even advanced designers/builders can still have
unexpected hum problems to solve. Hum is always a challenge in tube
amp design. With time you will become more intuitive and speedy in
your ability to diagnose it though.I'm sure you'll conquer it and feel good having done it.
Good Luck.
Follow Ups:
Thomas:You recommended the Morgan Jones book "Valve Amplifiers," but did so for its information on grounding. Did you mean "Building Valve Amplifiers," Jones other book.
My understanding is that "Valve Amplifiers" delves into circuit analysis (actually, I just discovered that you can sneak a peak at it through Google books).
BVA is the one with a detailed grounding discussion; it's worth the money for that alone. But... the fact that the hum comes on immediately, before warmup, limits the possible causes.
Thanks T.M. Good advice will be taken.
Jim
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