I modified my NC2000 with a second bias source, and screen current monitor/shut down circuitry. DONE ON A SINGLE PERF BOARD mounted where the original single bias circuitry was located.
So I have a NCL-2000 have fixed all the missing and blown up parts except the 8122. Unfortunately I can't find a working set of 8122 matched pulls. So will most likely just junk the otherwise perfect amp. Its going down for the last time, once again does anyone have a known working matched pair of 8122 pulls. Amp will be parted out Feb 28,2018 if I can't obtain a pair. Yes there are NOS on flea bay but no matched pairs and they want $450 each from RFP. at $900 that's more than than a working amp with tubes is worth.
With a small bit of work the Svetlana 4CX400A/GS-36B is a better and more rugged tube than the 8122. Many have also used a single 3CX800A7 which uses the same socket. If already on hand a pair of 8874's can also be used Carl
Good morning, I have a factory matched pair of 8122v1's and several other matched pairs in the 2nd and third bias quadrants. I match them at 100ma and 550ma. What parts were damaged? Good luck with the radio Regards Jim
I have eight 8122s ,. I need a tube puller to check them out they were bought over Ebay a few years ago, there were 2 matched pairs in the bunch. I would like to buy a puller if you have one will pay your price. Do not like the idea of changing so many tubes without help. Am ok on QRZ Ian EI3Y. Thank you for reading my post.
No they are spares I picked up on Ebay, filaments check OK. They look good they are not burnt very much on outside I intend to check them in my Ncl 2000 which I am repairing at the moment. Carl said some time ago that it was better to use a puller... checking eight I feel would be safer with the puller. The pair in the Amp at the moment have not been replaced since I bought it about 1967 and were working fine before I removed the power supply to replace the caps. If you know of anyone with a puller who wants a home for it I would appreciate you telling them of me. 73 de Ian EI3Y
I had an NCL-2000 for years -- pretty fine amplifier, and a pretty one, too. I'd think a tube puller would be mostly appropriate for tubes that have been socketed and used for a very long time, so the pins get "stuck" in the sockets. For swapping a lot of tubes in and out over a brief period of time I doubt one would be of any benefit (at least, not any I can think of). Maybe you mean to remove the ones that have been in there for 50 years.
If I want to test the spares I will have to remove the original ones the reason the old ones have survived I put down to the fact that when I bought the amp from Ted Dames W2KUW a friend of mine. I had to change the wiring to Irish 220v ac. which is now 230v ac I decided to use an auto transformer 220v to 110v for the valves . I was using this set up for a long time before I realised there was no switch on the transformer ..it was connected permanently so filaments were on all the time. This accounts for the long life of the 8122s. The first computer used to break the German codes in UK had a thousand tubes in it and when it was turned on each morning at least 40 tubes had to be replaced the engineer who build the computer told the operators not to turn off the tubes and there were very few tubes replaced from than on.
Maybe. I wouldn't attribute "long life" to leaving the heaters on all the time; I attribute it to good materials and manufacturing processes plus careful operation, being sure to never exceed grid and screen current ratings. I have 50 year-old 4CX250Bs in my homebrew 2m amplifier which for many years was used every single day at "more than rated" output power (about 1kW output for two tubes, with very good cooling) and they still work fine: Similar tubes, actually, but with a more robust pin/socket system. The heaters were only switched on when everything else was. I just never drove it to any real grid or screen current (not more than 2-3 mA for either, controlled by loading). I knew Ted W2KUW (I'm originally from New Jersey, as was Ted -- he lived 20 miles from me) pretty well and we did a lot of equipment swapping back in the late 60s to mid-70s. Nice guy, he used to deal a lot in surplus test equipment.
