Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on October 05, 2021, 02:52:36 pm
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I’ve had this tube for a while, l don’t have a tube tester and wonder if the tube is any good. I usually match tubes by their mA readings when in a fixed bias amp, the tubes that draw the mA’s within 2 to 3 points l assume are matched..?
This RCA black plate, made around the late sixties production reads way high when trying to match it with other 6L6s which are also black plates. It’s mA readings are over every tube l try to match it with by 10to 15 mA’s.
The tube seems to play ok in a single ended amp but is microphonic when tapped. Sometimes the single ended amp will make static like sounds when tapped but tap again it stops.
Does this tube sound like it has an issue..?
Perhaps, l should just use my ears and forget about the high current draw readings and microphonic sounds?
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> ...reads way high
> mA readings are over every tube l try to match
How high is high? Numbers?
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Well, in a 6L6 amp a tube pair that reads 35 mA’s each, this tube reads 45mA’s when l replace one tube with this, change no bias.
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Well, in a 6L6 amp a tube pair that reads 35 mA’s each, this tube reads 45mA’s when l replace one tube with this, change no bias.
Probably not a big deal. I believe I threw away a pair of 80s-era 5881s that pulled nearly double the plate current of normal 6L6s.