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Yaesu FL2000B troubleshooting

Discussion in 'Amateur Radio Amplifiers' started by NZ5F, Jan 12, 2011.

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  1. NZ5F

    NZ5F Ham Member QRZ Page

    I just set up a Yaesu FL2000B to my FT920 transceiver and everything is set up as per instructions in both manuals.

    1) I have both the relay and ALC connected directly to the transceiver as per the instructions in the FT 920 manual. I have a proper separate ground for the amplifier.
    2) My transceiver is reading 50W at peak power on the MFJ 962C antenna tuner with my RF power knob on maximum (This could be a potential issue with the exciter input not being high enough).
    3) My preferential settings for max ALC on the FT920 is 100W output for Antenna A (which is my default antenna) – which means that there is no max limiter on output power
    4) Upon transmit with the amplifier on and warmed up, my MFJ wattmeter is reading 100-150W. So there is amplification taking place. I am utilizing the plate and loading current settings for the bands as per FL2000B instruction. I am wondering if I should increase plate current to offset my low input signal to the amp. If I do this, should I increase the loading current then by some proportional amount (SWAG).

    I am trying to figure out what I am doing here that is limiting amplifier output. There must be some type of tweak that needs to happen. I am getting closer I think and might try adjusting both plate and loading current upward to see if that helps.
  2. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    That amplifier uses a low pass filter input and should be close to 50 ohms. It is possible that one of the input capacitors is bad but not likely. The most likely culprit are the sweep tubes. If one or more is bad it will change the impedance seen by the input circuit and of course you will have reduced output. Actually 50 watts of drive should give you about 500 to 600 watts out.
  3. K9STH

    K9STH Ham Member QRZ Page

    Are you seeing the 150 watts output using a continuous carrier or is this when talking? If when talking then this pretty much indicates that you are putting out full peak power since an average reading wattmeter cannot follow the voice peaks. Between 20 percent and 25 percent reading on the wattmeter indicates that you are putting out full power and any reading that is much higher indicates that you are no longer linear and that spurious emissions including "buckshot", in band noise, etc., are being transmitted.

    Although mfj "claims" that this is a peak reading wattmeter it definitely is not. Looking at the schematic shows a capacitor in parallel with the meter when in the "peak" reading position. There is absolutely no way that just by putting a capacitor in parallel with the meter will allow anywhere near peak power to be indicated accurately on the meter.

    Glen, K9STH
  4. NZ5F

    NZ5F Ham Member QRZ Page

    Glen, the signal modulates with the voice meaning that power appears to be fluctuating on the meter. If I am reading your post correctly, this could mean that I am actually transmitting properly at full power and the MFJ is not a proper wattmeter in terms of accuracy.


  5. K9STH

    K9STH Ham Member QRZ Page

    That is correct.

    What does the wattmeter indicate when you tune up using a constant carrier?

    Glen, K9STH
  6. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    I'm not sure how you could tune up the amp in SSB mode. Since you are tuning in CW you should see the correct amount of grid and plate current specified in the manual. Again, that is an old amp and sweep tubes are not bullet proof.

    Also, you didn't say if it worked before or if you just got it. If you just got it then you might want to check the power transformer. The power transformer has taps for 120, 220, and 440 volt operation. If for some reason it was wired for 440 volts then the maximum output would be about 150 watts.

    I can send you a copy of the manual if you need one.
    Last edited: Jan 12, 2011
  7. NZ5F

    NZ5F Ham Member QRZ Page

    Thanks to one and all for their insight on this. I believe that I have it set up more or less properly. I will need to do further tests including getting a proper wattmeter in line to check power out accurately. I will post a finalized set of findings once I get the proper wattmeter to check it out.
  8. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Sounds good, you should be loading up around .9 to 1 amps plate current at full power.
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