[Amps] Tuning

[Mike Sawyer]

"Why not do a bench test with a good dummy load and a wattmeter?  Make a
chart, and tune up in your favorite hangout area...."
To ad to that, you could purchase an antenna analyzer, adjust your antenna 
tuner/transmatch for freq. for 50Ω. Then all you would have to do is hook up 
your amp with minor adjustments and minimum QRM. I don't usually speak 
highly of MFJ products but my -259B is outstanding and recommend it over the 
AEA/Timewave version. Either way, you are transmitting into ~50Ω.
Mike(y)
W3SLK

----- Original Message ----- 
From: "Harold B. Mandel" <ka1xo at juno.com>
To: <kwasny at netzero.net>
Cc: <amps at contesting.com>
Sent: Wednesday, December 22, 2004 1:24 PM
Subject: Re: [Amps] Tuning


Dear Daryl,

The question of how far can you QSY without tuning is a mixed bag of
information.

Essentially, the point of resonance is at a particular frequency, and
shifting
that frequency throws the amplifier off resonance.

The point of resonance may have a broad occurrence whereby a "flat top"
to the peak power is observed.

Every amplifier is different. Six Commanders, side-by-side, will exhibit
six different  curves for resonance.  The choice of tank components
will also affect tuning bandwidth. For instance, in the dual 3CPX1500A7
amplifier just completed here, the Plate Tuning vacuum capacitor was
originally
a 12~500pF and that had a broad bandwidth, but lousy 160 meter
performance.

A 7 - 1,000pF cap was installed instead, and it has great top band
performance
but razor sharp tuning.

Why not do a bench test with a good dummy load and a wattmeter?  Make a
chart,
and tune up in your favorite hangout area, and while the amp is keyed at
minimum
drive, QSY 500 Hz., and see if you need to re-tune.  Change bands, change
frequencies
and chart the results. You will see the amplifier has different
requirements in different places,
but your chart will remind you in the heat of the contest that Yes, you
need to peak, or
No, go ahead and get 'er done!

Sincerely,

Hal Mandel
W4HBM
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