Tube lifetime

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

A friend showed me a recent post on another board that looked both interesting and valuable. The original poster gave me permission to cross-post here. This comes from the Studio Backroom List (an offshoot of the Ampex List) and the poster actually worked in the Sylvania tube factory many years ago. Here's the post, sorry I don't have the earlier context:
============================================
NO, NO, NO. this is an urban myth....You can ruin a tube
faster with low heater/filament voltage than most any other
way. The Cathode/filament is designed to operate at a very
specific temperature. Too high a temperature and you will
cause junk to outgas from the coatings and dirty up the tube
and its vaccuum. Too low atemperature and the coating will
not produce enough electrons to support the tube and the
current is now dependent upon the heater power and not the
grid or other tube electrodes that are doing the
electronics.
If the tube has very high electric field at the cathode it
can rip material off of the cathode if it cant get electrons
accellerate and absorb the energy. Not a pretty sight. Even
though the plate voltage is low in tubes used in microphone
applications, the electrode spacing is quite small and the
fields can be quite high.
The life of the heater is designed to be 50,000 hours (5.7
yrs) for normal consumer tubes and up to 200,000 hrs for
military/commercial grades. The cathode usually goes before
the heater on power tubes, but on those used in a
microphone, it will die from old age first.
The heater are much more abused by vibration and fast
voltage application than by burning away. There is a very
good reason for leaving tubes lit as the current inrush in
poorly designed filament circuits will spin those heaters
wires at about 1000 RPM inside the cathodes and cause
filaments to droop and possibly bang in the grid or just
break from all that bending. If the heater voltage is
applied with a current limited source, the heaters will last
forever on small tubes.

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Topic - Tube lifetime - Paul Joppa 22:18:32 01/9/02 (8)

Re: Tube lifetime - Jim D. 09:16:16 01/10/02 (2)

Re: Tube lifetime - Charlie G 10:16:23 01/10/02 (1)

Re: Tube lifetime - Jim D. 13:29:06 01/10/02 (0)

Re: Tube lifetime - dave slagle 09:09:14 01/10/02 (3)

Some background info - compliled from manufacturers' design guidelines - mb-de 12:18:25 01/11/02 (2)

Re: Some background info - compliled from manufacturers' design guidelines - dave slagle 14:17:48 01/11/02 (1)

Colour TV Booster/Damper Diode as turn-on delay - interesting thought... - mb-de 04:23:46 01/12/02 (0)

Re: Tube lifetime - PÃ¤r 00:03:21 01/10/02 (0)

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