[ETO_Alpha] Alpha 78 Tune/Load Settings

[Glenn AE0Q]

Hello Joe,

  I work at Alpha and just checked my files on a bunch of 78 tuneup
charts that I've collected over the years while working on repairs.
The typical numbers are TUNE=70 and LOAD=16, plus or minus 4 or 5 each
way.
  The main thing to remember is that all Alpha amps (except the Alpha
6) should have the knobs (or dial plates) set to these numbers when
the tune and load caps BOTH have the plates fully meshed:
TUNE=100
LOAD=ZERO

  The LOAD setting will vary depending on the output power you have
the amp operating at, more drive = more output with the LOAD set
farther clockwise (closer to 100).

  Don't forget to unplug your amp if you remove the cover to check the
alignment of the dials, and don't turn it on with cover off and the HV
shorted!  That will blow the step-start resistors..

73 - Glenn AE0Q



On 2/19/08, Joe Staples <w5asp at earthlink.net> wrote:
> I would like to know what is being used as the recommended Tune & Load
> settings for an Alpha 78 on 80 M.  For many years we have been using a Tune
> setting around 20-24 and Load at 78-84 on three different Alpha 78s.  Where
> the original numbers came from is a mystery but they have apparently worked.
>
> However our old Alpha 78 manual lists Tune - 65 and Load - 30.  This is
> nearly the reverse of what we've been using.
>
> Recently there have been reports of a 2nd harmonic on 40 M.  We've checked
> to see that the amplifier is not being overdriven ... we keep the grid
> current at 1/3 scale (50 ma) max. and seldom use more than 1200 watts out on
> the Bird.  It's possible that the harmonic is originating in the xcvr and
> just being amplified.
>
> Thanks for the help.
>
> Joe, W5ASP


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