[Amps] Solid State Amps

[Carl]

My NCL-2000 amplifier uses 8122 tubes. The day they fail, I will junk that
amplifier, because NOS 8122 tubes are scarce and expensive. I just see them 
on
eBay, offered for a starting bid of $750 for one pair! That's the starting 
bid,
not the final selling price... Sometimes there are lower prices, but there 
is
always some doubt whether the tubes sold are truly NOS, or are pulls in 
unknown
condition sold as NOS. Some years ago I wanted to buy a set of spares, and 
got a
quotation for some made by Burle, not RCA. The quoted price threw me off my
chair! I could have bought a complete new amplifier for that much.
------------------------------------------------------

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. You can do this with other tubes including 
the 4CX250/300/350 family. Use copper pipe slit to fit to adapt the 
different sizes.

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 and it is now less restricted. Use silicone rubber sheeting to 
fabricate a chimney to direct the air flow.

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

Carl
KM1H