Old Filaments

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

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