Re: Toob vs. Tube

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

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

Tesla list wrote:

>Original poster: "Rich" <rdjmgmt-at-socket-dot-net>
>Original poster: "Ed Phillips" <evp-at-pacbell-dot-net>

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