[AMRadio] My Amplifer Quest took a strange turn today

Bill Smith hbco2 at sbcglobal.net
Sat Apr 21 00:28:40 EDT 2007

----- Original Message ----- 
From: "Bow" <kd5kzn at sbcglobal.net>
To: "'Discussion of AM Radio in the Amateur Service'"
<amradio at mailman.qth.net>
Sent: Saturday, April 21, 2007 3:06 AM
Subject: RE: [AMRadio] My Amplifer Quest took a strange turn today

Thanks Bill..

Any idea about the input impedance? For now, I will be running it with my
Icom IC-718, so I need to figure out that interface!



Have no idea what the input impedance might be.  It has a SO-239 on the back
as an input, so expect it will be somewhere around 50 ohms, but could be
anything and will probably change with frequency.  If you have a small
antenna tuner, you might hook it up between the IC-718 and the input.  Or,
if not, hook up the IC-718 directly, but run it at low power (5 watts) and
check the SWR.  Frankly, I'd be surprised if it was a close match.  You can
set up a small coil and capacitor (L section) as input tuning without too
much trouble if you wish.  The amp will probably take much less than 100
watts to drive it to full output in normal operation.

Don't overdrive the amp in AM.  Recall that the carrier + sidebands take 4 x
carrier PEP.  If the amp is rated at 800 watts, don't run it at more than
200 continuous.  You'll need a fan as the power transformer and tubes will
heat up fairly quickly at that power level.   I'd plan to run it at no more
than 150 watts or so to keep things comfortable.  Depending on the plate
voltage, even that might be a little high.

There is no reason to push the amplifier, you will be at an advantage over
the 25 watts of the barefoot IC-718.  To get a 3-db increase in a receiver,
you need to double the power of the amplifier.  +/- 50 watts won't make all
that much difference if you are at the 150 watt level.


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