Re: [Amps] Two quick loading questions

[Rob & Terri Sherwood <rob@sherweng.com>]

I have always been puzzled by the "maximum smoke" tuning recommendations 
of some amps, AL-80A or B, for example.
A single 3-500Z in linear service is rated at 400 mA plate current. (350 
mA in class C).
When I used to run a Measures/Kessler modified TL-922A (pair of tubes), 
I tuned it as follows:
800 mA on the plate and 150 mA on the grid for SSB.  If I was running 
CW, I tuned it for 200 mA on the grid.
It was very easy to adjust the plate tuning for a grid current peak, as 
opposed to trying to see a broad plate current dip.
When tuned for the 800/150 mA conditions, the amp was very linear at 800 
mA, and would saturate at something approaching 900 mA.
I always monitor my amps with a Tektronix scope, and set the RF envelope 
at 6 divisions at the above plate/grid current conditions.
With a modest amount of speech processing to control the peaks from the 
exciter, it is easy to see the linear flattop a bit above the 6 scope 
divisions.
Set the drive on the exciter to peak the amp at 6 divisions, and I am 
completely confident I have a clean signal.
Without a scope, it is difficult to know how hard to drive the amp.  The 
ballistics of analog meters is all over the map.   My Alpha 76PA was 
very different from my TL-922A meters. My present Alpha 99 and 89 amps, 
even with LED metering, are not peak reading devices.  In these two 
Alpha examples, if the power output is set for 1500 watts key down, the 
LED meters read about 800 watts on voice peaks. 

R.Measures wrote:

> Tuning for max P-out with max-drive is more important than looking for 
> a dip.
>
> On Feb 9, 2005, at 12:39 PM, George KB2Z wrote:
>
> > I'm sure I'm not the first to ask. I have searched in the archives 
> > and did not find a solid answer. I apologize up front and am not 
> > trying to waste anyones time. The directions from different  
> > manufacturers dont seem to answer one way.
> > As I read the loading instructions for gg hf amps, (2x3-500) they 
> > should be fully loaded at full power then the loading increased 5 to 
> > 10% to lower the Ig and help stabilize the output. This seems to be 
> > where it gets confusing for me.
> >
> > 1) After increasing the loading 5 to 10%, should the plate be re-dipped?
> > 2) If drive is reduced from 100 to 50W, should the plate be re-dipped.
> >
> > Thanks in advance,  George KB2Z
> >
> > _______________________________________________
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> > http://lists.contesting.com/mailman/listinfo/amps
>
> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
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