----- Original Message -----
From: Jon Ogden <jono@enteract.com>
To: Jim Reid <jreid@aloha.net>; <amps@contesting.com>
Sent: Tuesday, October 26, 1999 3:57 PM
Subject: Re: [AMPS] RF Surge Problem
>
> Jim Reid wrote:
>
> >I use an Alpha-Delta-4 switch with which I select between
> >my Ten Tecs and Yaesu transceivers, and previously the
> >950SDX
>
> Well, if the Alpha-Delta has 40 dB of isolation then:
>
> 100 Watts = 50 dBm
>
> This means that 10 dBm still gets to the Yaesu front end. 10 dBm is 10
> mW. Enough to blow it up? I doubt it but who knows.
>
> > As I understand, you are to tune up using
> >pretty high power, then back the drive back such that
> >you actually will output only 1500 watts peak on SSB;
> >this method is supposed to get you max linearity and
> >lowest IMD products. So I have been tuning up at
> >around 3kW into the Bird load.
>
> Actually, I don't think this is really the appropriate way to do it. You
> should really tune up at your operating power. Perhaps I'll start flames
> coming at me or a debate, but I would think an amp is optimized for a
> particular output power when you tune up AT THAT POWER level. The tune
> and load settings for 1500 Watts are different from those of 3KW. So you
> are actually operating your amp somewhat mistuned in this fashion.
>
> Rich Measures is one of the big promoters of tuning up at high power.
> What I think Rich's point is that you don't want to tune up your linear
> at 100 Watts out and then turn up the input to 1500 Watts out. That will
> certainly cause mis-tuning. I will say however, if you want to tune up
> at 100 Watts out, fine. Just then re-tune when you bring your power up
> to 1500 Watts out. Tuning at low power will get you in the
> neighboorhood, but the final tune positions for high power operation are
> definitely different. I've confirmed this.
>
> The optimum load impedance of the tube will vary with drive level as the
> plate current which is a component of the load impedance figure varies
> with drive. So IMHO, the opitmal load for the tube at 3 KW is definitely
> different than 1500 W which means if you tune for the 3KW situation, yet
> operate at 1500 W you aren't operating with maximum gain, efficiency and
> I think as well, linearity.
>
> The amp should really be tuned up at the desired output power level.
If you want all the fine stuff listed above, you should tune the amp up using
the plate voltage and current that you used to design the tank circuit with.
Why go to all the trouble to carefully figure plate load, tank Q and coil taps,
only to operate at some arbitrary level? The amp will be as close to optimum
as you can get when you plan your design, and stick with it. If you want to
lower the power, back off the mike gain.
(((73)))
Phil, K5PC
"The Dark Ages were caused by a Y1K problem."
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