Transmitter overshoot on IC-7610.

Discussion in 'Amateur Radio Amplifiers' started by KB5SET, Feb 6, 2020.

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  1. KB5SET

    KB5SET Ham Member QRZ Page

    I have a new IC-7610 and a AL-80BG amplifier.
    The G stands for Grid Protection Circuit.
    I have problems with transmitter overshoot, or that's my guess.
    If I set up the amp to work on ALC and set the radio to 100 watts, it trips the ALC module.
    The ALC is set to pass 70 watts, the factory maximum recommendation.
    If I turn the radio down to 65-70 watts and load the amp heavy, the problem disappears.

    Anyone have this issue or any recommendations?
     
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    There is a quick pulse of power at the 100 watt setting that isn't controlled by the ALC, at least not right away.
    That pulse of power is sufficient to trigger the grid protection circuit.
    It appears the IC-7610 is sufficiently controlling it's power at the 65 watt level to prevent this from occurring.
    To set the ALC key at the 65 watt level and adjust the ALC control to where it just barely causes a reduction in input power.
    Keep using the IC-7610 with the power set to the 65 watt limit when using the AL-80. You can increase power to 100 watts any other time when not using the amplifier. The difference in reception at the other end of a contact will be almost unnoticeable between the 65 and 100 watt settings.
    As a suggestion leave the IC-7610 set to 65 watts at all times. Won't hurt a thing.

    Hope this helps
    73
    Gary
     
    K0UO likes this.
  3. AC2RY

    AC2RY Ham Member QRZ Page

    There is no need to use ALC at all. Use output power trimming to the level that is needed to reach full power from amplifier (easy to do by switching to RTTY mode). For SSB mode set compression and microphone gain for the best balance between peak and average power and do not touch power trimming at all. Keep in mind that required excitation power level from transceiver may be different on different bands.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    To prevent the grid protection circuit from tripping, always load the amplifier heavily.

    A recommendation from the amp's actual designer is to turn the load control more clockwise from the "max output power" point until the output power drops off slightly (and you'll see the grid current reduced on the panel meter at the same time) and leave it there. Obviously, re-tuning is required with band changes or fairly large frequency changes within a band.

    I think the "G" circuit is silly for the AL-80B, as a 3-500Z can handle a lot of grid current and normal tuning even with much higher drive levels than 65W can run it very safely as long as the amp is heavily loaded.

    BTW, the AL-80B (I've never used the "G" model) has a really good ALC circuit that is active, dynamic and not frequency sensitive. It controls the exciter based on monitoring the 3-500Z grid current, and not the "drive level," which are two different things; and it's very fast, adding no discernible group delay I can find. As such, it works with every rig having an ALC input I've ever tried, and that's at least a dozen different rigs.
     
    K0UO and K0OKS like this.
  5. KM3F

    KM3F Ham Member QRZ Page

    I've seen this kind of thread question many times before and caused me to take a new look at my KW TS 2000 action.
    I noted on it's HF power scale that when power is turned down from 100 into 50% range that the power meter reading will 'hang' [one bar alone] near full reading then disappear.
    This suggests there is overshoot until the power is reduced below about 40 watts.
    This has never been an issue but now looks like on this radio it can be seen on the radio's own power meter.
    I have an idea how this can be solved outboard and unconnected of any radio, but have to put the hardware together and test it to be sure it works as intended.
    .
    Not apart of this thread but also see there is a separate meter reading that moves according to SWR as compared to an outboard SWR reading on the 2m and 70cm bands.
    There is no markings or anything about it in the user manual.
    Another tidbit is the carrier level setting that is not in the user manual to optimize AM operation so the carrier is not attacked on modulation peaks causing the carrier into level reduction on peaks..
    For you KW TS 2000 users.
     
  6. AA7QQ

    AA7QQ Ham Member QRZ Page

    I just use flange mounted attenuators on all of my SS amps.

    Ed
     
  7. W5UAA

    W5UAA Ham Member QRZ Page

    Sounds like the symptom you're describing is that your AL80B GOP circuit is kicking the amp into standby because your IC7610 is not responding to the ALC voltage in time. Your "ALC LIMIT" control on the back of the AL80 may not be adjusted correctly. (page 4 of the manual describes the opposite symptom and calls it "motor-boating".

    Page 15 of the manual describes the "ALC LIMIT" control on the back of the AL80B and why it's provided (because ALC voltage requirements for exciters have never been standardized.)

    Page 17 of the manual describes how to properly adjust the "ALC LIMIT" potentiometer on the back of the AL80B. However, those instructions are kind of convoluted. Since the AL80 puts out -10 volts ALC with the "ALC LIMIT" control potentiometer on the back of the AL80B in the fully counter-clockwise position, and it puts out 0 volts of ALC with it in the fully clockwise position, and the IC7610 takes a range of -4 to 0 volts ALC, a good place to start is to put this potentiometer in the number "6" position if you look at it from a 0 to 10 position from counter-clockwise to clockwise numbering system.

    And of course, it's even better not to totally rely on the ALC and just reduce the power out of your IC7610 to 70 watts when using the amp.
     
  8. N3DT

    N3DT Ham Member QRZ Page

    KM3F, I've got a TS2000 and don't see any overshoot. At least in CW or SSB. I tried it with my LP100A in peak hold mode which LP says is good enough to measure any overshoot. I tried it at 20M for 100W, 75W, 50W and 20W (using the Power setting from the 2000) and in no case in either CW or SSB using FT8 did I find any indication of overshoot. It came right up to what I set the power at. At 75 and 100W I did notice a tiny 1W blip that started off in FT8 but then as soon as the modulation started, it went right to the wattage dialed in. Now I'm using DTR in FT8 to switch the ACC2 PTT. I'm not sure what happens when one uses VOX PTT, which I think most people are using. I don't notice it using my 80B either. I really don't use the ALC control either, I keep it set at about 4 which will allow the 2000 to put out maybe 80W before it goes into action. The only time I've had the GOP board go off was when I sock 100W into the 80B while it's not tuned. I've also got the QSK board, it makes for a real nice system and quiet operation too. No relay clacking. I do hear the 2000 relays a bit.
     
  9. KM3F

    KM3F Ham Member QRZ Page

    N3DT, i'm not sure what/why my 2000 display is showing the 'suggestion' until I get a chance to investigate.
    Maybe nothing but who knows until it's looked at.
    What I have just done was test on 160m into a dummy load at full power, reduced power at several points and see no hang.
    Switched to antenna that does not match, do the same test over and now see the hang as before.
    This suggests to me that if the match is near perfect the power dial back won't show if there is no mismatch even with the power dialed back because the circuit for 'fold back' is the same as for SWR that does the fold back and for ALC control.
    When there is a mismatch, it becomes a different story from the above test.
    If you look at the circuit, the SWR, Pwr dial back, and ALC all involve the same circuit via diode feeds to keep isolation between each source.
    I don't have any issue with spiking but it's not to say it's not there as of the moment under certain conditions.
    The observations are not done driving the AL80B that is more than 25 years old.
    I cannot see the use of grid protection on a modern radio/80B combination under any circumstances. Seems is causes unnecessary 'con fugility' to the user for no advantage.

    Thanks.
     
  10. N3DT

    N3DT Ham Member QRZ Page

    Well, just this morning, I was using 100W on 15M and switched to the 80B because of a YO that couldn't hear me, forgot to turn the power down and whammo, the grid protection turned off the amp. Now it may not have done any damage in any case, but it's quick and nice sometimes. The 80B meters just twitched and the amp went off and I immediately knew what I'd done. He never did hear me though. I notice some stations seem dead deaf. There's one in LU that keeps calling and he never answers, and he's got a good signal too.
     

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