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November 9, 2008
News - Tube Amps in the Age of B…
about 4 years ago
P.P.S. Another reason to bring the HT up slowly is to the electrolytic caps time to polarize
(especially if the amp has been shut off for a long time). Tubes worked good with tubes--
mixing them with solid state is a tricky business (as a lot of guitar amp designers have
learned the hard way).
P.S. Normally there's no DC though the output xformer, so no big field. But funny things happen during
start up, or when speakers are connected or disconnected. Also relays contacts can bounce. All it takes
to get a big voltage spike is to get a field going and then suddenly collapse it. You're starting with 350 VDC...
Great project. As you probably know, you're getting the pop when the HT comes on because
the HT supply is solid state and comes up in a hurry--no cathod heaters to warm up. :-)
Putting a relay on the speaker connections is a bad idea because of self-induction in the
output transformer. It could easily exceed the max. plate voltage and blow the output tubes
or a cap. One possible solution would be to use a use the regulator to switch on the HT
gradually (say was a capacitor w/bleeder resistor chargers on the regulator input).
Speakers should never be connected or disconnected from a tube amp while the amp
is turned on.
No public wish lists :(