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Thread: Yaesu FL-2100 amplifier reduced power

  1. #1

    Default Yaesu FL-2100 amplifier reduced power

    First question is: Does it hurt an older tube amplifier if I run it at reduced power?

    Here's the deal. I loaned my 2kw watt meter to a friend. Long story short, it got broke. Got a new one on the way. Probably another week.

    I have other watt meters and equipment that have wattmeters built in. But these are all max of 300 watts. Obviously, I don't want to burn up my wattmeter, antenna tuner, etc...

    So, the question is, can I go through the normal tuneup process with my transceiver going to my amp, but when I get up around the 275-280 watt mark, stop adding power from the exciter? Will the amp be harmed if it's not running at full power?

    The thing is, I know I could tune the amp without a wattmeter. Simply adjust the plate for dip in current. But I'm not sure how to adjust the load without a wattmeter. Do I also adjust it for the lowest current possible? Even if this works, and the current looks good on the amp, I'm not comfortable running the amp if I don't know the RF Power out. So, I was thinking that if I used my 300 watt meter and tuned th amp to 300 watts and stopped, it would be OK. At least until I get the new wattmeter.

    What I don't want is to hear that 300 watts out isn't that much of an improvement over the normal 100 watts. That it's only a 3db gain. That there's no advantage. etc... I know all that. I simply want to know if there are any negative affects to the amp if during the tuning process I simply stop at 300 watts? Most people who want to run at lower power, usually TUNE for the max 100 watts and then they LOWER to exciter. The amp's manual simply say that input power is 100 watts PEP. Doesn't mention intentionally wanting less power. Thanks... mike...

  2. #2
    K7KBN's Avatar
    Join Date
    Jul 2008
    Bremerton WA USA


    As long as things like plate current and grid current are not exceeded, the amplifier should not be over stressed. I have to note that the FL-2100 series is only rated at 600 watts output (IIRC they were rated at 1KW DC INPUT). That was several years ago, before RF wattmeters were readily available for less than Bill Gates' net worth.)

    And I wouldn't put a whole lot of faith in the accuracy of ANY meter designed for the amateur market unless it has been recently calibrated or at least cross-checked against such a meter. I've seen cheaper meters off by as much as 25 per cent - and I've seen Bird 43s off by that much as well. Brand-new, out of the box, is generally safe and reasonably accurate.
    Pat K7KBN
    Semper ubi sub ubi.

  3. #3


    Thanks for the info Pat. Like I said, I don't have my decent wattmeter that can do 1kw; but I don't like tuning up an amp without a wattmeter. Sort of need to be able to tune plate/load for max RF and keeping current down. But the only wattmeters I have; until my replacement comes in; are 300 watt limits. So I wanted to run the transceiver/exciter at a lower level to not exceed 280-300 watts and potentially harm my meters, tuner, etc... Thanks for the information. Mike...

  4. #4


    Erm, you might need to revisit your calculation; 3dB above 100W would be 200W.


  5. #5


    Quote Originally Posted by G7RUX View Post
    Erm, you might need to revisit your calculation; 3dB above 100W would be 200W.

    You are 100% correct. But that wasn't my point. My point was I didn't want someone saying running the amp at only 300 watts is pretty much a waste of time, because a 300 watts won't make that much difference on the distant end vs 100 watts. And even less when you consider SSB doesn't peak the 100/300 watts on a regular basis.

    I wanted to stick with the issue of whether an amp that is intended to run 600+ watts output, would have any negative effects only putting out 300 watts. Sort of like how most cars are more efficient and drive better at highway speeds than driving at 25-30mph.

    Anyway; it looks like there shouldn't be an issue. This is only a temporary thing until I get my replacement wattmeter that can handle the higher wattage. Thanks... mike....

  6. #6

    Join Date
    Dec 2008
    Elgin, Illinois


    You haven't mentioned what type of a HF transceiver that you're using and whether you vary or reduce the RF output by 3 or 6 db which would reduce the RF output from the RF amplifier. I run a 6N2 KW driving it with only 10~15 W Output and 300 W Output from the amplifier. My Tempo 6N2 KW uses a pair of 8874s Ceramic Forced Air Cooled Tubes in Grounded Grid. My amplifier really requires at least 75 W RF Drive which I have a small buffer amplifier to accomplish this task to produce the 1200 to 1500 W P.E.P. RF Output on 6 or 2 m SSB.


  7. #7
    G4FUT's Avatar
    Join Date
    Jan 2012
    Barnard Castle; Teesdale Co. Durham


    If you are using SSB, then simply turning down the mike gain on the transceiver will NOT reduce its output power. However some modern transceivers now have a facility to turn down SSB output. What TX do you have?
    Jon G4FUT

    Even if the voices aren't real, they have some pretty good ideas

  8. #8


    Turning down RF power is not a problem. I am running both an FT-857D and an FT-897. (Same exact radios; mobile and base version). Anyway, I can lower the RF Power anywhere from 100% to 1%. I just wanted to know if I fed the FL-2100 with 30-50 watts to get 180-350 watts out of the amp; if that would be a problem on the amp. Thanks for the feedback. Mike....

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