What do you mean by "a lot of metal inside of the envelope?" I've got brand
new tubes from various manufacturers that appear to have as much or more
"metal" as these used tubes (if I understand what you mean).

I'll agree that a tube tester isn't a crystal ball, but based upon my
experience over several years (restoring CRTs) emissivity seems to be the
best single predictor of remaining tube life. Of course it won't predict
shorts or other catastrophic failures, but it is useful.

Nest'ce pas?

Jon

From: (Scott Dorsey)
Organization: Former users of Netcom shell (1989-2000)
Newsgroups:
rec.audio.tubes,alt.guitar.amps,rec.audio.pro,aus. hi-fi,rec.audio.marketplace
Date: 12 Apr 2004 10:03:31 -0400
Subject: FA: Quad of Rare Genelex KT-88 Tubes

Jon Yaeger wrote:

I gather you're so experienced that you can tell more about a tube from a
casual analysis of a mediocre digital image than my Hickok Tester can using
empirical analysis. Guess I'll just send you photos in the future and
dispense with the dials & switches . . .

You need to do both. A transconductance tester will only tell you that a
tube is currently good, it won't tell you how long it has left. If you have
a lot of metal on the inside of the envelope, it's a sign that the tube has
a lot of hours on it.

On transmitting tubes, there is an elapsed time indicator on the transmitter
and you are supposed to log tubes in and out with hours of use when you
replace them. You don't get this on audio gear, sadly.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Hi Fred,

Yes. Usually. However, I've owned tubes with
"tired" looking getters that still tested and
functioned well, for a long time.

Probably even more so with small signal tubes.

I have two Sylvania VT-231 (JAN-CHS-6SN7GT, with
US Navy boat anchor sign). One of them has a perfect
getter, the other one has a translucent/brownish
getter so bad, that one usually would expect it to have
gone to triode heaven by visual inspection alone.

But both tubes (all 4 sections) measure (and work)
_perfectly_ the same under real load and as a matter
of fact two days ago I had to wade through 10 supposed
to be top quality current production EH 6SN7 (gold pin
version) to find a pair (4 sections) which measures
as close (mu and gm) on all sections like the 50-60
years old Sylvania ones, which are _not_ from the same
batch, by the way.

While it's true that I'd gravitate more towards a tube
with a pretty getter than one with an ugly one, that's
not necessarily because of a rational assessment.

I second that, at least with my limited experience.

Tom

P.S.: Follow up snipped to RAT only.

--
Okay, maybe i am paranoid. But that doesn't mean
they are not out to get me. - unknown