Tube Tester Problems / Confusion

[Doug Taylor]

I am experiencing a problem I believe with my tube tester. When I was
testing some ECC83's, I think my tester fried the tubes. I have an old
green metal cased Sylvania Type 202 tester that is in very good cosmetic
condition - I realize that means nothing about the electronics "under the
hood", but it looks like it had a good home for many years.

The tube scroll chart shows the ECC83 tests are identical to the 12AX7
tests - are these tubes truely identical, just the European nomenclature
system vs. the American?

It lists two sets of settings for two separate tests. I ran the first
one which showed all was well (transconductance & emission test through
pin 3). I would then run the second test shown and got a wierd result.
I would run through the short tests and they were fine but when I
switched to do the trans/emiss. test (through pin 1), the tube would
light brightly and initially show a 110-120 reading in the good range.
After a few seconds the needle on the tester would quickly fall until it
barely read 10 on the 0-140 scale. I then reran the first test and now
the trans/emiss test showed the tube was bad. I tried testing another
tube that I knew was good and the same thing happened (two NOS RCA's down
the dumper?). What is going on - a bad tester putting too much
current/voltage to the tube on that second test? Is there something I'm
missing in testing the preamp tubes? I had just tested a quad of 6550's
and it seemed fine - identified a heater to cathode short in one of the
tubes.

Any help/opinions/ideas are greatly appreciated.

[Bill Hatcher]

Doug Taylor wrote:
>
> I am experiencing a problem I believe with my tube tester. When I was
> testing some ECC83's, I think my tester fried the tubes. I have an

Might be a problem with the filiment voltage. If the second test
setting had a serious increase in filiment voltage the tube will be
ruined pretty quick. Sometimes you can take a weak tube and
rejuvinate it by bumping the filiment voltage up to ONLY the next
highest setting for a SHORT period while you watch the filiment heat
up and glow very brightly. This is reputed to burn the surface off
the coating on the filiment and allow a fresh surface to put out some
more (electrons) I think. I have found that this extends the tube
life only a little. I don't reccommend it for serious audio
applications. Too bad about the NOS RCAs. Bill