14 Mar
2013
14 Mar
'13
7:37 p.m.
On 03/14/2013 02:18 PM, Mouse wrote:
One area where gassing can occur is around the pin and other lead seals.
Getter is most cases work best at operating power. 4-400s, 3-500Z need
to run at dull red plate to make the gettering effective.
If there are any ceramic metal power tubes they also become gassy and
Need to be put into service carefully (usually 24 hours under filament
and then under bias enough to heat the tube but at lower than normal
voltage. I used to do the 90day rotation of 4cx3000 and 4cx10000 in
commercial FM service.
General care, vibration is bad, shock is worse, heat and cold can stress
the pin/lead seals. Use care to not wipe off markings. Do not scratch as
that can lead to envelop cracking with temperature changes.
With care many tubes last lifetimes, others no matter what, they die.
I have a lot of old radios with original tubes functioning at nominal
levels and likely continue for many more years.
Allison
I have
wondered what the rate of gas infusion through glass is at
STP, i.e. how long before the vacuum is reduced enough to affect tube
parameters. 200 years? 1000 years? 10,000 years?
Depends on the gas, among other
things. Hydrogen, for exmaple,
diffuses annoyingly fast through pretty much anything. (Annoyingly
fast for those who want to contain it, at least.)
I suspect it also depends on how much getter function is left. The
getter's whole point is to capture stray bits of gas; as long as it
lasts, it'll be scavenging up any stray molecules that do find their
way in. I suspect internal outgassing is more significant than
diffusion through the body of the thing, in most cases, though.