New TL-922 Owner

Discussion in 'Amateur Radio Amplifiers' started by G3YRO, Dec 14, 2016.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    I've just acquired a Kenwood TL-922 Linear . . . (something I've been hoping to get for the last 20 years!)

    Gave it a good clean inside before switching it on. It all looks 100% un-modified.

    After reading various articles online, the only modification I decided was worthwhile was to directly ground the grids. So did that . . . and tried it it out. It's producing 1200 - 1300 watts carrier output into a dummy load, so presumably that means the 3-500Zs are in good shape?

    Do the valve filaments and PSU take much of a hammering on switch on? Ie is it really worth adding some kind of soft-start circuit? If so, I would probably do something really simple like a 10 ohm resistor in series with the mains feed (240V), shorted out after a second.

    The HT drops from 3.5kV to 3kV on full power - is that about right? (ie are the electrolytics working OK?)

    Also - should there be some lights illuminating the meters?

    Roger G3YRO
  2. W1QJ

    W1QJ Ham Member QRZ Page

    On normal 240v ac line voltage the HV is about 3000 volts in ssb and drops to 1900 or so on cw. Your numbers are way high. You might have the mains strapped for 200v which would raise the filament voltage too high. A step start never hurts but w hen you switch between cw and ssb there is still a surge. You really do need a soft key as the relay voltage is 120 vdc and not too many radios like that. Grounding the grids gives more power and reduces drive. You may check out W8JI for his recommendations. But don't go too far with hair brain voodoo.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah about the CW/SSB switch. I'd leave it on SSB permanently and never switch that; however I thought the power limit in the U.K. was 400W (?) and if it still is, then the CW position would be more appropriate, and just leave it there. Don't flip that switch with the power turned on!
  4. G3YRO

    G3YRO Ham Member QRZ Page

    Yes I've read W8JI's suggestions, which seemed to make sense compared to many of the other suggested mods I have read . . . that's why I went for a multiple path grounding of all the grid pins . . . and won't bother with those big hairpin anode stoppers!

    As I only plan to use this on the LF Bands, don't see any need to re-ground the Tune variable cap.

    The Amp is wired for 240V . . . I'm only going by the indicated HT voltage on the front panel meter, so maybe that needs re-calibrating. What I was REALLY asking about was how much it normally drops on full load . . . as that would give me an indication as to the state of the electrolytics in the PSU.

    In terms of adding a soft-start circuit, I thought the biggest issue was the filaments taking a lot of current on switch on? Having said that, there is no big THUMP on switch on with this amp . . . unlike my FL2100 !

    In terms of switching the Amp to transmit, both my Transceivers have proper relay contacts to do that, so no need for any interface.

    Anyone know whether the meters should be illuminated?

    Also, it came with the original Manual, but there isn't a complete circuit in there . . . presumably if I find a Service manual online, it will have the full circuit diagram?

    Roger G3YRO
    Last edited: Dec 14, 2016
  5. W1QJ

    W1QJ Ham Member QRZ Page

    Yes, the meters do light up but it is common for the bulbs to eventually burn out. All yours are probably burned out. It is a pain to change them. You may never find the original ones. I would engineer some sort of LED work around if I was you.
  6. W9GB

    W9GB Ham Member QRZ Page

    Roger -

    Kenwood TL-922 Service Manual Service manual.pdf

    In 2012, Don Kessler assembled a kit of commonly requested upgrades (LED illumination of meters, QSK, Electronic Bias, Soft-Key, and Step-Start) for the TL-922(A) HF amplifier, that he calls The Revival. The PC boards used are high quality FR4.

    You can read the Manual, that he wrote, to understand the changes and level of work.

    The Kenwood TL-922(A) amplifiers, that I have seen over past 25 years, usually had rotary switch issues (many from non-tech illegal CB operators, operator error/damage).
    An Asian seller was selling a replacement and Multi-Tech offered an adaption of their commercial offering.

    Lou and Carl have seen far more TL-922(A), and can advise of most commonly seen issues.
    Last edited: Dec 14, 2016
  7. G3YRO

    G3YRO Ham Member QRZ Page

    I have a load of small wire-ended pygmy bulbs, so will probably just use those.

    Thanks for the links Greg . . . will download that Service Manual.

    Don't think I would do the mods suggested by Kessler . . . this amp has only had one careful owner, a pre-WW2 amateur, so he knew how to look after valve equipment! He passed away 12 years ago, and his son has merely turned it on occasionally (to keep the electrolytics working), but never actually used it.

    I don't think it's had much use at all, as everything looks very pristine inside.

    I'm just going to do a very simple 1 second mains input delay to reduce inrush current.

    Roger G3YRO
  8. KU3X

    KU3X Ham Member QRZ Page

    I had a TL 922 here for a short time. Great little amp. I am sorry I did not buy it.
    If you DO NOT put a soft start in the amp, always turn the amp on with the voltage switch in the CW position. That's your step start for the HV
    power supply. All of my home brew amps that I ever made have step start time delay relays.
    To soft start the filaments on those tubes is a great idea and highly recommended. What Heathkit did many years ago in their SB 220 amps was
    to use light gauge wire on the filament choke to help dampen the filaments on start up. This is not necessary on tubes like the 8877's and 4CX1000's.
    But it's highly recommended on tubes like the 3-500's. Running a tad less filament voltage per tube is also good.
    What the commercial guys do in big transmitters is to turn the filament voltage down until they see a drop in output power. Then they bring it back
    up to where the output power levels off. This extends the tube life.
    Just because you don't hear a big clunk on start up does not mean that there is not a spike.

    Barry, KU3X
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    But if you do that, it's best to just leave the switch in the CW position forever. Flipping the TL-922 switch from CW to SSB while the amp is turned on is probably the leading cause of failures of TL-922s. The switch is very underrated for what they did and is an accident waiting to happen.

    The SB-220 inrush current limiting is mostly done by its transformer design and they don't need a soft-start unless someone replaced the transformer with a different one.
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    This is the page Lou refers to: Aside from all the bizarre stuff Tom removed, pay attention to grounding of the CTUNE and 3-500Z grids. You want low reactance. That said, the method I used to ground the grids in my SB-220 results in the LOWEST reactance:
    Using scissors, I cut strips of soft copper. Hardware is #4-40.

    I also use the W7RY QSK setup, using FAST hermetically sealed relays. Even if you don't use Morse, it's an improvement over the OEM setup. The worst-case relay time is 1ms (faster than the fastest rig can produce RF). "Hot switching" becomes a thing of the past. Like the SB-220 board, the TL922 board also supplies electronically regulated and switched bias. The TL922 board also drives LEDs for the meter and indicator lights. Jim also offers a step-start board that uses better quality resistors than the Harbach or other units. See

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