Carl,
There are alternatives Manfred.
Get a pair of 8072's and some defunct 8122's. Machine off the finned
radiator and push onto the 8072.
That's a good hint. I had read it before somewhere, but forgotten about it. I
have now stored your message in my NCL-2000 folder, for when the tubes fail.
You can do this with other tubes including
the 4CX250/300/350 family. Use copper pipe slit to fit to adapt the
different sizes.
I have a lathe, so I can actually turn adapter parts if necessary.
Ive even tried the anode cooler from shorted 3-500Z's slipped over the 8072,
they actually run quite well to 1200W out since that blower puts out a lot
of air
Mine doesn't, because it's a 60Hz blower and here in Chile it has to run on
50Hz, so the airflow is drastically lower. I compensate partially for that by
running the tubes at a lower idle current than normal. So far people say that
I'm not splattering, so it should be OK.
Convert to the Russian GS-36B or Svetlana relabled 4CX400A. Change to the
Svetlana SK2A socket and a new filament xfmr. Other voltages are compatible,
even the bias. It also has a much more stable screen that is not prone to
current drift. Written up in the 90's by Svetlana and George Baxter, W6TC.
Use a single 3CX800, same socket, minimum reworking. A bit tight in places
but done by many.
Get a bit creative and adapt a pair of Eimac 3CX400U7/8961 and use it as a
8874. Real cheap, even NOS as there is no replacement application since all
the 800-900 mHz Motorola cell and other cavities have been retired.
http://lists.contesting.com/_amps/2012-06/msg00442.html
When the time comes and the 8122 tubes fail, if that happens before I have my
final super top solid state amplifier up and running, then I will consider what
to do. Maybe they never fail, because I use that amplifier only rarely. I'm
somewhat allergic to noise, and the blower noise is highly irritating to me. Not
when I just switch on the amplifier, but after half an hour or so of constant
blower noise, I start going up the walls, and shut off the amplifier. That way
the tubes last long! ;-)
Several years ago I installed an acoustic labyrinth at the air inlet, and
replaced the oil by the thickest grade that would allow it to run. The noise got
slightly lower, but not much.
I often think that when the tubes fail, that would be the cue to get rid of the
noisy beast!
Manfred
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