[Amps] 572's

[kingwood]

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