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Re: [Amps] Correct way to drive an amp with controlled carrier AM?

To: "jeremy-ca" <>, <>
Subject: Re: [Amps] Correct way to drive an amp with controlled carrier AM?
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Fri, 24 Aug 2007 07:38:24 -0400
List-post: <>
> Using a SB-220 as the example how should it be run for 
> maximum clean signal?
> What is the amp efficiency at that point?

Without a PEP meter that catches the peaks really well or a 
scope it is nearly impossible to properly set up a 
controlled carrier rig.

My personal preference is a PEP meter, and I use the AWM30. 
It can catch and hold very short peaks. I also have a scope, 
but that is just mainly to watch negative peaks. It's far 
too difficult to see flat topping on voice peaks with a 
scope with a standard trace, but very easy to watch negative 
peaks and not flat-line. The DX60 can have considerable 
distortion if mistuned or if the grid drive is set low, or 
if the audio is run too high.

There is also a modification on the screen to vary carrier 
level that really adds a lot of distortion if you run the 
screen out of the optimum range. I tried that mod in several 
of my DX60's and found it could cause very bad modulation 

What I do with is use a standard oscilloscope to compare the 
audio sampled from the modulator section low level amplifier 
and the RF output. I adjust until the modulator is linear on 
the trapezoid. Then I simply duplicate the settings. I don't 
think most people would do this, since they care less about 
overall linearity as long as it doesn't sound muffled. I had 
good results with three DX60, one DX60A, and two DX60B's I 
own with the modulator component values on my web page.


If the guy doesn't mind running the 220 a little hard, the 
procedure would be to load the amp to absolute max output in 
the SSB HV position with the DX 60 on CW tuned for max out. 
He should see 1000 or 1200 watts carrier.

Then when he goes to AM he has to watch the peaks on the 
meter and stay a few percent below the power peaks he loaded 
the amp to when he tuned. I found best linearity in a 
220/DX60 combo was with 850W PEP output on AM. That was with 
the 220 in the SSB position.

The real problem with the DX-60 is you can't really adjust 
drive levels without creating non-linearity in the 
modulator, but the good thing is it is a good match for the 
SB220 drive power on AM.

73 Tom 

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