You can also run it in the CW position for 3dB less heat (-;
Carl
KM1H
----- Original Message -----
From: "Manfred Mornhinweg" <manfred@ludens.cl>
To: <amps@contesting.com>
Sent: Sunday, October 19, 2014 1:17 PM
Subject: Re: [Amps] Solid State Amps (or rather the NCL-2000...)
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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http://ludens.cl
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