tubes age 121
2) Did they toss the tubes when they failed on a tube tester or failed in the
radio?
3) Do the tubes you use fail at the rate that the Navy tubes did?
4) Did the radios have tube or solid state rectifiers?
The last question is the most interesting. Even in 24/7 type service I don't see
anything close to the Navy failure numbers. I also do not run tube rectifiers so
maybe all their failures were rectifier tubes. What's more to the point, back in
the 1980's your government and mine went out and bought tubes for "essential
equipment" to keep it running for something like another 20 years. The good
old R-390(both A and not A) *must* have been on the list. The mountains of
tubes we see on eBay are a result of them surplussing these tubes. You can
find all the tubes except two - the ballast tube and the rectifiers. I can
understand the ballast tube, it's a different category and probably didn't get
covered in the order to buy the vacuum tubes. The rectifier may have been left
off since the solid state conversion was an approved modification. If that's the
case then they didn't go through anything close to the number of tubes they
thought they would. I suspect that most of us on the list have more than ten
sets of spares. Heck I'm probably not that odd in having a couple hundred of
some of them. Hall of fame land may be in the multiple hundred sets range.
We're all out grabbing these tubes and they are still dirt cheap. There have to
be an ocean of them out there. We don't run as many radios as the Navy did,
but then they didn't plan on a 500 year supply of tubes either.
Bottom line - fancy tube shields are neat and they do look slick. For a truly
presentation grade radio they are the only way to go. If you put a couple
hundred bucks into the front panel then they are cheap by comparison. For a
use it every day and I don't care what it looks like radio, save your money ....
Take care, Bob Camp
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Date: Tue, 22 Apr 2003 22:20:23 -0400
Subject: Re: [R-390] Re: IERC tube shields and tube temps...a field expedient...
Even with an indirectly heated cathode the contact between the filament and the
cathode is very good. The insulation (vacuum) around it is also really good. The
result is that the cathode gets to the filament temperature and isn't affected very
much by what's around it. The self regulation of the filament still keeps things
going at a constant temperature. Given that then tube shields aren't going to
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