Replacement of RCA 8122 Tubes

Discussion in 'Amateur Radio Amplifiers' started by N2OTG, Jul 12, 2015.

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  1. KE0ZU

    KE0ZU Ham Member QRZ Page

    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.
    N2EY likes this.
  2. K7BIT

    K7BIT Ham Member QRZ Page

    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.
  3. KM1H

    KM1H Ham Member QRZ Page

    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

  4. K9AXN

    K9AXN Premium Subscriber QRZ Page

    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
    W5MW likes this.
  5. EI3Y

    EI3Y Ham Member QRZ Page

    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.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Are they stuck in their sockets?
  7. EI3Y

    EI3Y Ham Member QRZ Page

    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
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    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.
  9. EI3Y

    EI3Y Ham Member QRZ Page

    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 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.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    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.

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