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Has anyone replace 3cx800 with Russian tubes

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Nov 16, 2019.

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  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    Anyone made a 3cx800 conversion with Russian tubes & sockets? Or 4cx800 replace 3cx800?
    Last edited: Nov 16, 2019
  2. MM0IMC

    MM0IMC Ham Member QRZ Page

    One is a triode, the other is a tetrode. Different biasing and a grid supply are required, I believe.
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    Screen supply minor inconvenience vs $1600 of new 3CX800 if they can even be found. Or possible grounded screen?
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    The Russian GI-46B triode is likely the best to replace 3cx800. Anyone try this?
  5. W1QJ

    W1QJ Ham Member QRZ Page

    I think I’d rather walk on glass than to try and transplant GU74b tubes in place of 3cx800’s. That’s just me.
    W1BR, KK4RSV, AE0Q and 1 other person like this.
  6. WW5RM

    WW5RM Guest

    Anyone run the GU-46B?
  7. MM0IMC

    MM0IMC Ham Member QRZ Page

    Is that due to all the broken 811a's and 572B's? :p
  8. W9GB

    W9GB Ham Member QRZ Page

    James -
    This question has been asked multiple times since 1990s,
    when surplus from the former Soviet Union began to appear.
    That surplus, after 30 years, is getting smaller and prices rising.

    In the same time period (1990s) long-time medical, military, and commercial broadcasters began their migration to solid-state designs — lowering order volume (sales) of ceramic power tubes.
    I find that this question is frequently asked,
    due to the COST or AVAILABILITY of the correct Replacement Tube.
    Converting from a Ceramic Triode to a Ceramic Tetrode REQUIRES a NEW Control Board,
    as well as power supply modification for Screen Voltages.

    I would NOT Advise. Plenty of failed DIY attempts (sold as amplifier parts on eBay).
    IF you can NOT afford, SELL what you have, THEN Buy what you Can Afford.
    PY2RAF likes this.
  9. W3PAL

    W3PAL Ham Member QRZ Page

    Yes, you can but it will require a new of modified power supply circuit. You'll most likely need an additional, custom made transformer or several pre-made transformers and a board with diodes, stabilizer and caps. You'll also need to modify the socket and the hardware to accept the larger diameter tube. Can you do this? Is there enough room for an additional power supply? You may also need to take extra measures to keep the amp from oscillating if you go with a grid driven configuration. Some form of negative feedback may be required too.

    As far as quality of Russian (or Soviet) made tubes, it's excellent. They are produced to military specs that are MUCH higher than general consumer specs. A GU-74B (4cx800 equivalent) will last for a long time, even with heavy use. Spare tubes are readily available and should be available for a long time.
    This is what's used in my ACOM-1000 amp. I like it better than Alpha because of better quality and attention to details. I run it hard, often pushing to 1200 watts. It's been a solid performer for 8+ years. I managed to get several new, replacement tubes for under $100 for both. I doubt I'll ever need them.
    MM0IMC likes this.
  10. MM0IMC

    MM0IMC Ham Member QRZ Page

    Likewise with my Alpin 100 MKIII, which is no longer manufactured. Thankfully, I picked up a spare GU-74B, which is still in the box (tested and works 100%).

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