[Amps] Solid State Amps (or rather the NCL-2000...)

Manfred Mornhinweg manfred at ludens.cl
Sun Oct 19 13:17:08 EDT 2014


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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