Thanks for that info Tom, Ive passed it along as well as your url. I had no
idea that you even had any old Heathkits.
Does the DX-35 suffer the same problems as the DX-60? I have one and may
decide to resurrect it some day. Meanwhile a Viking I and HQ-129x recreation
of my late 50's station are giving me enjoyment.
----- Original Message -----
From: "Tom Rauch" <firstname.lastname@example.org>
To: "jeremy-ca" <email@example.com>; <firstname.lastname@example.org>
Sent: Friday, August 24, 2007 7:38 AM
Subject: Re: [Amps] Correct way to drive an amp with controlled carrier AM?
>> Using a SB-220 as the example how should it be run for maximum clean
>> 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 linearity.
> 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.
> See: http://www.w8ji.com/heathkit.htm
> 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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