Ameritron AL-80B – After some time….

Posted by on August 17, 2011

Following up after a couple of weeks and revised after a couple of months.

I’ve now tuned the amp at a few points in each band into a dummy load.  This gives me a good reference chart on initial tuning, as well as a record of output, grid current and plate current.  This makes it easy to tune, but also easy to tell over time if anything has changed.

I’ve since installed the 10/12 meter modification and installed the grid overload protection board.  The 10/12 mod was easy, following Ameritron’s instructions after sending them my call sign info, etc.

The GOP install was also easy, but took some time.  I went slow, being careful to confirm and triple check everything.  In the end, it worked first time, apparently as designed.  When I deliberately detuned, it clicked back to standby somewhere just over 200 Ig, as expected.  This adds peace of mind.  I think the ALC on this amp, when set correctly, probably serves nearly the same function, as it can cut your exciter’s output as Ig gets into this range.  I wanted the extra backup.

Along with the complete setup and tuning above, I also now have the ALC properly set up.  With the front panel ALC SET near minimum (CCW), I get low output only (maybe 25%).   At 12 o’clock, I get full output, but added drive level on the transceiver has no effect, except driving up the ALC voltage reading.  In normal operation, I run ALC SET around 1 PM (6 on the dial).  This gives ALC protection and probably slight compression, but with minimal ALC action.

I do tune a little differently now (note ALC keeps power down in the first phase and must be hooked up for these instructions to apply):

  • Confirm frequency, Band switch, antenna switches
  • Set 75 percentage carrier exciter out (roughly 75 watts I presume)
  • AL-80B ALC SET to 2
  • Set Plate and Load to the values in my helper table (initially the manual values)
  • Intermittent carrier (cw zeros at high speed; switching to an MFJ tune keyer once it arrives)
  • Maximize RF output on Plate then Max output on Load (cycle back and forth a couple times quickly)
  • Leave Load a little clockwise, anticipating higher power
  • Grid current (Ig) below 200 ma throughout, 150 when tuned — critical in the next tune cycle
  • Plate current (Ip) target around 450 when tuned at operating power
  • Increase ALC SET to about 6.0
  • Maximize RF output on Plate then Max output on Load (cycle back and forth a couple times quickly)
  • Leave Load just slightly clockwise

I then go on the air, probably around 80-90% power potential with my ICOM at roughly 75% exciter drive (on some bands, I do use a little more drive).  The process takes only 10 or 15 seconds at most for both tuning phases.  I have a full power dummy load that I use if I feel more than a tweak is needed.  If I QSY on a close freq, I just do the second pass.

In operation, The meter hovers in the 700 to 800 W area during voice peaks.  Audio reports continue to be excellent so far.  I think the ALC compresses a little at this level, but mostly protects the AMP.

So far great experience.  This has really opened up 40M for me and soon will be helpful on most bands.

 

73….W4LI…. Dan Hoogterp

 

 

4 Responses to Ameritron AL-80B – After some time….

  1. Bert Stephens

    Hi Dan. I just read the info you gave on the AL80B updates with the 10/12 meter band anf the grid overload protection. I plan on doing both in the near future. I am using a icom pro II and set my power output knob to 60 watts and I read the al80b showing 1kw . According to your staement you drive the amp at 75 watts and get 700 to 800 watts. Your output seems a little low at 75 watts drive. I am wondering if it is due to the grid overload protection . Thanks for the article and I will work on the mods after I send Ameritron the info they need . Have a good day. Bert WA8LEN

    • Dan Hoogterp

      Bert,

      Thanks for the note. This is probably differences in meter calibration (radio or amp), tube variance, etc. I don’t recall seeing any change when installing the grid-overload-protection. Since it seems to operate like a circuit breaker – shutting off operate mode when the amp exceeds grid current, I don’t think it could affect operating gain.

      I think the GOP is worth it, but reasonable care in tuning with the ALC hooked up also provides very good protection. I just wanted to be extra careful.

      Best Regards and 73
      Dan, W4LI

  2. bill

    hi I have a ameritron al-80b just asking what is the lows drive power you can put in the al-80b
    I am ask this for a friend

    • Dan Hoogterp

      You have one — asking for a friend? Interesting.

      This is a difficult question to answer effectively, given the ambiguity of what you are trying to accomplish.

      The lowest drive in my experience is zero. The amplifier successfully emits zero watts, when fed with zero watts PEP, even if the keying line is activated.

      If you mean useful power input, I’d guess it would work with 16 watts PEP, about equal to a fully modulated AM CB signal. That would give roughly a 160 watt output. That is a terrible – and illegal – use of this amp. Fortunately, I doubt CB’s have a keying output, so that would be your friends biggest challenge.

      If your instead thinking of using it with a QRP rig, then I apologize for the CB reference. It should provide about 10 DB of gain, when properly tuned to your maximum PEP output.

      Best,
      Dan