ncl 2000

HI
I HAVE GOT A NATIONAL NCL 2000 AMP,BUT THE 8122 VALVES ARE NO GOOD I WONDER WHAT OTHER VALVES I CAN PUT IN THE AMP?
THANKS FOR THE HELP
73 DE WOLF G4SSX

 

There really aren't any.

The 8121 is a "similar" tube with transverse (crosswise) cooling instead of vertical (through the base and up through the fins) cooling; however it's rated for lower operating voltage and power and of course the cooling system would have to be very modified to blow air across the coolers rather than through them as it's set up now.

8122s are available, they're just expensive!

 

The 8072 is the same as the 8122 except that it doesn't have any "fins". It is made to work in a coaxial loading assembly that also acts as a heat sink.

Glen, K9STH

 

I'll bet I could get those to work using the BeO thermal links that come with a lot of old Motorola base stations. But the heck with it, as I have nothing to experiment with here right now.

My friend Miguel W6YLZ has an NCL-2000 which I converted for him to six meters, and of course the tubes failed over some testing time, or screwing around, or whatever. The 8122s were ultimately replaced with 4CX250Bs! Obviously, the sockets had to be changed, and some re-wiring was required (and screen voltage had to be lowered), and the 4CX250B can't handle quite the power of an 8122; however when all was done, it still makes a kilowatt output on 50 MHz and now uses really cheap and very readily available tubes!

Now if he goofs up and blows the tubes, a reasonably "new" pair (surplus NOS) can be had for about $100. Not a bad deal.

 

Finding good 8121's is about the same as finding 8873's.

There are several swaps that work.

- A single 3CX800A7. same socket, rewire for GG and keep the drive at 50W or less. Make a new anode strap and chimney from red silicone rubber.

- A pair of Ruskie 4CX400A/GS-36B. Use the Ruskie ceramic socket. Original chimney and anode strap fit. Wire filaments in series, other volatges are compatible; bias circuit may or may not require a simple mod to obtain 125 ma idle current per tube. I did this conversion for George Badger of Svetlana USA years ago.

- A pair of 8874's. Same socket, wire filaments in series, convert to GG. Use Alpha 76-78 series input or just leave the swamping resistors as in a MLA-2500. There are still reasonably cheap 8874's showing up from working decomissioned cell phone amps.

- A pair of 8072's. Use a propane torch to unsolder the anode cooler from 4X150/250,300, 350, 8930 scrap tubes. Use copper pipe to adapt them to the tube. The bigger the anode the closer you get to 400W Pd. The 8122 cooler is welded, you could try grinding or machining it off.

Carl
KM1H
Member of NCL-2000 Design Team
National Radio 1963-69