My friend just bought a quad of Alpha branded E84L tubes to test. They seem fine tested as a 6BQ5 but gave him a loud hum in his guitar amp as soon as they came up. Any idea why?
usually this is due to a bad tube dragging down the plate supply. I never heard of "Alpha". It is probably a junk brand from the bad old days (before the industry collapsed in the late 1980s).
JJ EL84s seem to be the best ones being made today. Unfortunately good NOS EL84s are almost impossible to find, so you'll have to use current production.
I would wonder why did your friend buy the new tubes? Maybe his amp "went west" and blew the prior set. Is he sure the problem is the new tubes or the old amplifier? -Dick
Alpahs aren't any good at all. So I think that may be one of the reasons why your tube might be bad. My brother use to have one. He bought it from the flea market and every single time he attempted to use it, he got the same results which was that great old humming.
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