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Yaesu ft-991A, Ameritron Amp, EF80-10

Discussion in 'Amateur Radio Amplifiers' started by KC3PGU, Apr 29, 2021.

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  1. KC3PGU

    KC3PGU Ham Member QRZ Page

    Newly thinking about an Amp I will have access to.

    Currently I use an end fed 80-10 with my ft-991A. Using my antenna analyzer the end fed has SWR ranging from 1.05 to ~1.6 (at 10) so I always use the internal tuner on HF and all seems to be just fine. Of course the tiny display on the 991A makes it difficult to see what the SWR ends up being after tuning.

    With the consideration of adding a gifted to me Ameritron AL800, I am wondering how to approach tuning. Do I still tune using the FT-991A at all? What range of SWR can the Ameritron tolerate? (don't see that in the manual), and do I need a tuner between the amp and coax, and does it need to be able to handle the max PEP the amp is theoretically able to output? I don't expect to be driving the amp to extremes on SSB. Do I really need a tuner rated to handle more than 500 watts?

    Lots of reading to do before turning the darn thing on I guess.
  2. NG1H

    NG1H XML Subscriber QRZ Page

    When the amp is off/on bypass everything in the amp is bypassed. It is as if it isn't there.

    When the amp is on and active the radio should see 50 ohms and any tuning is done by the amp or something between the amp and the antenna feedpoint.

    Go by your manual but as a rough rule of thumb most tube amps can handle at least a mismatch producing a 3:1 SWR. Solid state amps are usually more sensitive to mismatch.

    From the numbers you gave it looks like pretty much anything would work without an additional tuner. Even the SS amps should be happy with 1.6:1
  3. KC3PGU

    KC3PGU Ham Member QRZ Page

    that's a great relief. I an not over 1.8:1 in any are of interest - upper 80, 40, 20, 17, 10 (which I'll have to mod I guess)

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The AL-800 will absolutely not require using your FT-991A tuner at all, when the amp is active.

    The AL-800 can output a kilowatt, so be sure your EF antenna can handle that, and possibly more. Even if you try to reduce power by turning the output of the 991A down, occasional peaks can easily be more than you think. The amp will easily handle 3:1 SWR, and probably quite a bit higher than that. Its LOAD control will tell you -- if peaking output power on any band requires setting the LOAD control to "0" or to "10," the amp cannot properly load your antenna system; however if it's really<2:1 on all bands, this should never be a problem.

    Watch GRID CURRENT with that amp: It is definitely the most critical parameter to watch. No need to watch the voltmeter (HV) because you can't change it. Not much need to watch plate current (Ip) because the tube in the 800 can handle more current than the amp's power supply can even deliver. The critical parameters are OUTPUT POWER and GRID CURRENT.

    That amp is best used with a 240Vac line. It will "work" on 120V, but line current can be very high; 240V is better for your house wiring, outlet, service panel, circuit breaker, and the amplifier itself.:)

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