Re: 4-125A, vacuum tube do's and donts

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Parpp807-at-aol-dot-com>

In a message dated 4/9/02 1:57:31 PM Central Daylight Time, tesla-at-pupman-dot-com 
writes:

> Check filament voltages.  Over driving the filament
>   will drastically shorten its life.  Need not be
>   fanatical about this, but check when new, and
>   from time to time.
>  

Yes, especially thoriated tungsten filaments which must be run very
close, 1 to 2%, of ratings so as not to exhaust the emission properties.
Also, The filaments should always be brot up to operating with a variac.
No plate voltage. Warm the filaments slowly before applying the HV. 
Reverse the process when shutting down. I run a lot of tubes in my
stereo amps. I never turn off the filaments but I keep them nice and toasty
at around 35% of full voltage. Many of the tubes are more than 20 years old.

Also, fingerprints on the glass produce hot spots. Keep the toobs clean.

HTH,
Ralph Zekelman