[R-390] re: maintenance

[W. Li]

I think that you must be a victim of a *surge*. Vacuum
tubes do not tolerate overvoltage or mechanical trauma
well. Operating them at design voltages in a stable
environment is the best way for a reasonably long life
of 10,000 hours (1.14 years if left on 24 hours a
day). 

Adding a cooling fan in hot environments is a very
good suggestion. 

Bill Kleronomos wrote a real good article in ER in
1994 (vol 66 page 10) entitled *Electron Tube Survival
Primer*. Perkins Electro Acoustic Research lab in
Canada ran some tests in which they found that running
a 6AK5W at an envelope temperature of 100˚C
resulted in a 50% tube survival at 5000 hours, but 80%
failed by 2000 hours if run at 253˚C. In the same
article, they found running heaters at 5.04VAC gave
the longest life (albeit at lower emmisions); running
at 6.30VAC had a 85% 5000 hour survival, but running
them at 7.56VAC led to a 20% 5000 hour survival. 

Hope this helps.

W. Li
Mercer Island, WA


       
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