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

[jeremy-ca]

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.

Carl
KM1H


----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>
To: "jeremy-ca" <km1h at jeremy.mv.com>; <amps at contesting.com>
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 
>> 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 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
>
>