Eddie,
First of all, there are no “stupid questions”, if they are asked with
sincerity. I really hesitated in answering this because I do not want get one
of the bilious, “as the stomach turns” threads going, as so often has been
happening on here, lately.
I do, and have done for yeas, 20 to 50 572B amps a year. Each one has
two tubes that are invariably flat when I get them in because of the extremely
high filament voltage they have been operated at in the HeathKit, Yaesu, and
other, amps.. Two tubes, times 20 to 50, equals a bunch of tubes. If them
come 10 per case, it is very easy to figure out how many cases I buy in any
given year. I am sure that Carl uses many more, than I do, because of the 6
meter mods, which I do not do.
Once the Chinese got there glass (porosity) problem solved about ten
years back, there 572B tubes have been, in both emission, and longevity (this
assumes that they were operated with the correct filament voltage, excellent.
The problem I mentioned only appeared in the last batch of tubes I bought.
Emission was only about 50 per cent of what had been in the past, and should
have been by specks. I do not know what happened at the factory, but something
did..
Think back and remember when you mistakenly plugged a 250TL into a rig,
thinking you were plugging in a 250TH. That difference is what I saw with the
last batch of Chinese 572B I had. If the factory gets the problem corrected, I
will continue to use them, as I really do not have a choice, or perhaps, I do.
How about a simple modification to install a single, horizontally mounted,
3CX800A7 in an SB-200, or Yaesu FL-2100? Filament voltage and cooling should
be the only issues of concern. The existing power supply should provide enough
power get around 1,000 watts PEP output. Then, with W7RY’s vacuum relay QSK
system, seems to me, you would be a great little desktop amp. I have been
running a Dentron MLA 2500, modified this way, for about three years (Not the
QSK). with absolutely no problems. My concern with this mod was mounting the
tube horizontally. This has not been an issue, up to this point. Comments?
73 de Lon, K5JV
Lon W. Cottingham
1110 Golden Bear Ln.
Kingwood, TX 77339
281-358-4207
281-795-1335 Cell
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