tubes age 142
was some thinking that reducing the number of tube types might be important
but I didn't see that mentioned. In the 390A, the design went to 6AK5W's for the
oscillators so either the low power consideration went out the window with the
demise of the 6AJ5 1st rf or the 6AK5 was deemed better for other reasons. I
didn't have the heart to change the resistors to match the 6AK5 design of the
390A. I'll probably look for more 6AJ5's down the road. Because I just re-read
this stuff, I mention it - I imagine most of you already know it. That's a pretty
interesting archived report Dan.
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Date: Mon, 06 Jun 2005 18:39:36 -0400
Subject: [R-390] Megacycle detents, nominal B+, and bad tube brands
<snip> And on bad tube brands: "JJ" (Eastern European manuf)
CC82's/12AU7's are not too good in the 5814A spots. I've had two develop
filament-to-other-element leakage that gave intermittent hum, just in the past
week. Luckily I have a good supply of JAN 5814A's.
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Date: Tue, 07 Jun 2005 10:05:02 -0400
Subject: Re: [R-390] Megacycle detents, nominal B+, and bad tube brands
<snip> >And on bad tube brands: "JJ" (Eastern European manuf)
............................
Thanks for the experience report on these tubes. If I remember right, the JJ
brand is sold into the hi fi and musician amplifier markets. It's possible that
those folks don't fuss as much as we do about tube life and the cost of
replacements. Also, it's possible that JJ simply got a bad batch of tubes. (I
suggest you send them back to them to see what their response might be. Of
course the minimum correct response is a set of replacement tubes by return
mail.) The reputation of eastern European tubes of recent manufacture is
generally quite good with a few exceptions (e.g. the "7199" tubes that turned out
to be another type altogether, enveloped with altered pinout and having remote
cutoff in the tetrode instead of the linear one in the real 7199.)
>Luckily I have a good supply of JAN 5814A's.
Shhh! Don't let on. Your security contractor will scold you!
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