tubes age 17
that otherwise minor microphonics are far more noticeable as well as the last
IF stages being over driven. When an IF tube is used as the S-meter amplifier
from AGC voltage is when the negative S-meter reading happens most often
from grid emission. The 390 doesn't do that so its different, though it uses a
separate meter tube to read AGC voltage, strong grid emission from a signal
tube can still drive the meter negative.
There is a Sencore tube tester made just for checking grid emission. I saw one
at a hamfest Sunday, but I already own one. Back in the day of tubes in
consumer radios and TV's GC made a little rubber hammer for testing tubes for
microphonics, just two pencil erasers on the end of a pencil but shaped like a
hammer.
There were shops that declared any other test was a waste of time, only the
grid emission test was good for trouble shooting because grid emission was
more critical to many circuits than the other tube parameters. And besides with
a sensitive enough grid emission tester (that was far more compact than the
Gm testers of the era) they could sell more tubes noticing the beginnings of
tube failure forecast by grid emission.
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Date: Thu, 04 Nov 1999 04:32:53 -0500
Subject: Re: [R-390] I.F. module
>NO. I said GRID EMISSION not plain emission tester. ......................
OOOPS! Sorry Dr. J, I stand corrected. Copied the list on this just in case
others are not clear or I mislead anyone with my last post -- as might happen if
we just let the thread end there.
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Date: Mon, 13 Dec 1999 00:59:35 -0600
Subject: Re: [R-390] 6AJ5 replacemnt
The 6AJ5 is basically a 6AK5 that works with 28V on the plate rather than
normal B+ voltages. Try each of the 6AK5's that you have. I'd almost bet money
that several of them them will work just fine in the R392.
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Date: Mon, 3 Jan 2000 17:59:55 -0400
Subject: [R-390] Massaging Tube
Anyone want to start a thread on which sockets should get the stronger tubes?
I have a hunch that marginal ones will work fine in certain sockets. I think it
was Nolan who says a well aged but not necessarily strong 5749 is best in the
PTO, but strongest 5749's should go in the earliest IF stages. How to allocate
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