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Re: Old Filaments
Original poster: "Ray von Postel" <vonpostel-at-comcast-dot-net>
Well I wouldn't say that not following my suggestion is a wrong thing.
It may or may not help. I usually start with about 1 (volt) on the filament
and then increase it about a volt at a time for at least 8 hours, sometimes
24 hours or more.
You have a choice of either 5 or 10 volts on the 304 TL/TH series of tubes
since they have two separate filaments in one envelope.
Commercial practice seems to have been to use a 5 volt transformer with a
center tap. I havn't had any experience with connecting the filaments in
series, 10 volt, and using the junction as the "center tap" to ground.
Tesla list wrote:
>Original poster: "Rich" <rdjmgmt-at-socket-dot-net>
>Well there is one more thing I did not do right the first time, I just
>checked the tubes for continuity. I do not have a transformer for more
>than one tube at this time, I will wind one for two tubes at a time.
>Approximately what voltage should I start at with my run up to 10v?
> >While the 304TL might be electrically rugged, its definately got some
> >mechanical issues. Awhile back i had a 304TL filament crack from some
>Have you tried bringing the filaments up to temperature over a days
>time? Use a Variac on the filament transformer so you can bring it up
>full voltage about a quarter volt at a time over a day. Once you have
>up to rated voltage leave it on for several hours. Thereafter, run the
>tube as normal. Some say the problem is caused by the migration of gas
>into the tube or from the residual gas left in the metal when they were
>new. This happens to new tubes that have been on the shelf for 30 or
>years. The slow cautious heating followed by a period at full filament
>current seems to help. I have had the same problems with the 24-G,
>152-TL, 304-TL/TH, 450-TL/TH, and the ZB3200 all of which are of similar
>construction. This may or may not help but with the cost of tubes is