Re: Old Filaments

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ray von Postel" <vonpostel-at-comcast-dot-net> 

Hi Rich:
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.
Good luck
Ray


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?
>
>Rich
>
>
>Big snip
>
> >"
> >While the 304TL might be electrically rugged, its definately got some
> >mechanical issues.  Awhile back i had a 304TL filament crack from some
> >
> >Ed
> >
> >
>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
>to
>full voltage about a quarter volt at a time over a day.  Once you have
>it
>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
>more
>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,
>75-T,
>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
>worth
>a try.
>
>Ray
>
>