Our amplifiers are called "Linear Amp" for a reason.
As we increase drive and increase power out, the grid current also goes up.
The amp is perfectly tuned at the point where you have the minimum amount of
grid current that will product max pwr out.
If we keep increasing the LOAD beyond this point, grid current will continue
to go up, but the pwr out will not increase.
This means your amp is no longer operating linearly.
One of the biggest mistakes people make with tuning an amp is, they keep
going up, little by little, hit the best point but don't realize it, and
then add a little more LOAD, and dip the PLATE current again. The see no
change in output power so they leave it there. WRONG.
At that point it is over-loaded, drawing more grid current than necessary
and on peaks it will be overdriven (non-linear), causing splatter.
IMO, once you reach the point of max power out, you should back off the load
control just a tiny littlebit , while carefully observing the power out. At
the first sign that backing off the load begins to drop the output power,
LEAVE IT THERE. That's the sweet spot.
That way you are sure you are not overloaded and not driving the amp into
its no-linear operating range on voice peaks.
EVEN BETTER: work CW; you don't have voice peaks! ;-)
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Robert
Mcgraw
Sent: Tuesday, June 25, 2013 11:20 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Amplifier Question
The tubes come to life in about 1 second. I usually wait until the fan is
at operating speed, typically 10 to 15 secs.
Watch the grid current.
I rarely look at FWD and REF values. The PEAK meter tells me all I need to
know.
To tune, always use a combination of drive from the exciter, adjust TUNE
for max output, increase drive while watching the Ig and Plate meters.
Adjust LOAD to keep Ig below 240 ma or the red line. Keep moving drive up
until you reach max power, Plate current 0.8A max, Ig 240/260 ma max.
Do not retune if you wish to operate at lower power. Just reduce drive.
73
Bob, K4TAX
> OK...
>
> 1) How long do I need to wait before my Centurion amp is warmed up
> and ready to transmit? The manual says nothing, and I am sure one
> should not key the exciter too soon. But... how soon is too soon?
>
> 2) What METER do you guys watch, and why?
>
> The right hand meter has four display options. I usually watch the Ig
> (grid current) meter option, as the manual says this is the most
> important parameter to monitor. It says it should not exceed 260 ma -
> I have never seen mine go above 240 ma at any exciter in level. Just
> one reason I think this is an easy amp to tune.
>
> Does anyone monitor any of the other three meter settings? If so,
> what are you looking for and why?
>
> The Plate meter hardly ever moves, and the FWD and REF settings do not
> seem very informative, because the scale markings are designed to
> convey Grid and Plate information, not power information - and the
> PEAK POWER meter on the right side more obviously indicates power out.
> I cannot imagine why one would watch the FWD or REF meter setting -
> but, know I still have a lot to learn...
>
> Any ideas?
>
> ============ THANKS ! / K8JHR ===================
>
>
> _______________________________________________
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> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
--
Disclosure:
I am a Tentec Ambassador and compensated according to the Tentec Ambassador
plan. I serve as a volunteer beta test person for the Omni
VII, Eagle and Argonaut VI products. Otherwise, I hold no business or
employment interest with Tentec.
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