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Replacement of RCA 8122 Tubes

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

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  1. DF5TP

    DF5TP Ham Member QRZ Page

  2. DF5TP

    DF5TP Ham Member QRZ Page

    Hi all,
    I happen to own 3 RCA 8122 tubes. They are unused in there original packages. One would have to carefully start them up, I think. Like turning the heater on for some time, then applying some reduced voltage at anode and grid 2. I bought them 1975.
  3. KM1H

    KM1H Ham Member QRZ Page

    Since this question wasnt a result of hitting REPLY, I just came across it by accident when someone gave me a LIKE on this vintage thread.

    There were 3 blowers used over NCL-2000 production from 1964 to 92. Ive been able to clean and relube most to long term working but none were built to last without lubing. I havent replaced any of mine.

    Grainger has a wide choice and last I looked had a suitable match for all versions. A Google search may turn up additional info.

    Let me know what you find so I can add it to the "library" here.

    A point made early in this thread which I just noticed was that simply matching idle currents didnt work on AB2 had me laughing since the NCL-2000 was actually AB1 in SSB with no grid current and AB2 on CW and other modes for higher efficiency.

  4. AF7XT

    AF7XT Ham Member QRZ Page

    I may be looking to ball bearing the fan in mine Carl. But first the bandswitch and the T/R relay.
    All this after a laundry list of of other projects ...
  5. KM1H

    KM1H Ham Member QRZ Page

    The getter for that tube is on the cathode surface and activated by filament heat. When they are stored for a year or more, there is no set rule for used or NOS, they should be run with filaments only for 24 hours minimum. I have had to run a few for up to 3 days before they stopped kicking off the overload relay when keyed with no RF drive.

    Those with some machine shop tools can adapt any number of anode coolers from defunct triodes and tetrodes and use on the 8072 and variants.

  6. AF7XT

    AF7XT Ham Member QRZ Page

    4cx250? The .OD is near enough but the .ID ?
  7. KM1H

    KM1H Ham Member QRZ Page

    The 250 isnt a 400W cooler but it can run at lower power, that powerful blower will help a lot. Ream out the center diameter or use brass/copper tubing to make it smaller, there are loads of tubes to choose from including truly bad 8122's.

    Get creative!
  8. W9DAY

    W9DAY Ham Member QRZ Page

    I know this is reserecting an old post, but Carl (KM1H) is there any documentation on swapping the NCL-2000 over to GS-36B? I'd like to convert mine but there's nobody around me that will do it and shipping is a bear on these machines.
  9. KM1H

    KM1H Ham Member QRZ Page

    I made that swap almost 20 years ago for George Badger, W6TC, SK, at Svetlana USA, and prior with Eimac using their new nomenclature 4CX400A/GS-36B. It was very straightforward, use the Svetlana socket, connect filaments in series with a dropping resistor (or use a new transformer) I used nichrome wire. He had a conversion sheet made up.
    Here is an ancient post I made on here.

    Voltages were nearly identical and so was the power except the new tube has much better IMD and internal reliability.
    As you can see the tube was apparently respecified later from the GS-36B to be a 8122 replacement.

    Ive also used it in the AM-6154 and 6155 amp conversions for 144, 222, and 432 MHz.


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