[Boatanchors] tube / tube tester question

[J. Forster]

Tubes can, and do, go gassey with extended storage. Gas molecules either
desorb from interior surfaces if the original bakeout was not perfect, or,
more likely, diffuse through the glass or seals.

SOME can be restored to useful life by operating them with filament AND
plate applied. Filament alone will NOT work with most "getters". The
reason you need plate voltage is you need a flow of high energy electrons
to ionize the neutral gas molecules so they chemically combine with the
reactive getter material.

Set the tube up in a DC test jig or tube tester an measure the leakage.
Then run the tube at about 20% of rated plate current for a few hours,
then retest the leakage. If it has gone down, continue. If not, the tube
is likely not recoverable.

Do NOT exceed about 20% Ip or you will PERMANENTLY poison the cathode and
kill the Gm.

Best,
-John

===============




> OK, let me try again... I had this note 'almost' done when my DSL went
> down..... sigh....
>
> Here's Ron's "DUMB question" of the day........
>
> I recently bought a nice RME VHF 126 Converter for 6M, 2M, and 220 MHz.
> I know it's not 'state-of-the-art, but I love my boatanchors. It will
> be paired up with my RME 6900 receiver. This converter has separate
> converters for each band. I expected to find a bunch of old caps in it,
> but the construction is excellent and uses 'dog-bone' and ceramic caps.
> Cool.
> There are a LOT of tubes in her. A quick test with my HP 8640B produced
> a signal on 6 and 2 at -120 dbm. 220 was dead.
> However upon testing the tubes, I found an extraordinary percentage
> "leaky". 7 out of 11!!!
> I have 2 tube testers, a Sencore and a Weston transconductance type.
> The results were the same on both.
> Unfortunately, I don't have spares for 6 of the bad tubes.
> The four 6BQ7As were all bad
> The two 6AM4s were both bad (short microwave tube)
> Since these tubes are multi-section, either one section was bad, or the
> other. Emissions were so-so. Some better than others.
> I have already purchased new tubes, but my question is this......
>
> Can tubes go 'bad' from lack of use lice electrolytic caps? I know
> nature abhors a vacuum, so maybe the seals just gave up the ghost.
> Will leaving them 'on' make any difference?
>
> Of the hundreds of boatanchors I've gone through, I have never had more
> than 2 tubes from the same set bad......
>
> It appears this converter was not used in a loooong time. The ground
> side of the electrolytic filter cap was open. Never seen that before....
> Strange.....
>
> thanks!!
>
> ron
> N4UE
>
> P.S. I AM working on the cap 'article'.....
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>