24 Jul
2005
24 Jul
'05
10:07 a.m.
And as found with Colossus, it's power cycling
that really
kills them, so keep that to a minimum and they tend to last
pretty well.
The fail rate can be reduced significantly by bringing the
filament supply up slowly, over a couple of minutes, and then
applying the bias supplies for a period, the longer the better,
before the HT is applied.
It's not unusual to see lifetimes of 150,000+ hours on
transmitter valves using these techniques and that's on valves
power cycled a few times each day.
Lee.
.
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24 Jul
24 Jul
12:40 p.m.
The fail rate can be reduced significantly by bringing
the
filament supply up slowly, over a couple of minutes, and then
applying the bias supplies for a period, the longer the better,
before the HT is applied.
It's not unusual to see lifetimes of 150,000+ hours on
transmitter valves using these techniques and that's on valves
power cycled a few times each day.
For transmitting tubes (valves), yes, careful power-up is important, but
for computer rated minis, not so much. If anything, the a slow power-up is
probably protecting the power supplies more than the tubes.
Computer rated minis fail, like most receiving tubes, due to a lack of
emmision. Weak filaments that lead to burnouts and loose elements that
lead to shorts generally get weeded out quickly, as the tubes die
prematurely.
The margin checking the /FSQ-7 did, as well as most tube computers, is an
old radioman's trick - reduce the filament by 10 precent. A strong tube's
gm will not change by much, but a weak one will take a dive in gm.
William Donzelli
aw288 at osfn.org
4:20 p.m.
You may have a point there. The worst tubes I've
had with regard
to shorts are recent Eastern European imports. Used tubes rarely
give me this grief.
From accounts I have heard, with tube computers and 50s
radars, the first
six to twelve months were hellish on the tube swapping techs.
Anyway, I think comparing the recent Eastern European tubes to 50s
U.S. tubes is like comparing pot metal to platinum. The 50s and 60s were
THE time to use tubes - the quality was very high (at least with the
quality brands), and the performance of the devices was unlike anything in
the 40s.
William Donzelli
aw288 at osfn.org
6934
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