Jerry:
Thank for the reply.
Actually I tune the amp initially with about 5 watts of drive from the
exciter then increase the drive to the point grid current approaches the red
line of 130 ma (2 tubes), then re-adjust the tuning and loading for max
output while keeping the plate current below 0.8 amp and grid current below
130 ma. Usually about 90 to 110 watts of drive will produce some 1400 to
1500 watts output. This nets some 2250 watts of DC input. 2800 volts @ .8
amp plate current. Efficiency is about 66% which is what I'd expect. I
then, without changing tuning on the amp, I reduce the drive to about 15
watts for 275 watts output. I always tune the amp for "max output" while
keeping the meters under the red line both on plate current and grid
current. Since the exciter has variable output, it is easy to achieve this
point in tuning without overdrive.
Just curious why the tubes show a good bit more color on 40 M than on 75 M.
Guess I best look at the other bands in case there is a parasitic lurking
around. However, no instability is noted at any time. I rarely use the amp
on any of the other bands except 160M and 75M.
73
Bob, K4TAX
----- Original Message -----
From: "Dr Gerald N Johnson electrical engineer" <geraldj@isunet.net>
To: <tentec@contesting.com>
Sent: Thursday, August 21, 2003 4:11 PM
Subject: Re: [TenTec] AMP Question
> Have you tuned for maximum out or for plate and grid currents? The plate
> and grid meters of a grounded grid amplifier can mislead you a great
> deal when tuning. Its far more effective to tune for maximum out, then
> adjust the drive for rated plate and grid currents. When you get maximum
> output you will have the correct ratio of plate and grid currents.
>
> I noticed that years ago in the Ft. Belvoir Army MARS station. One night
> the S-line and 30S1 that I'd been using to work my dad was broken and
> the bands to Nam were closed so I took over the new KWM2-A and Henry 2K
> for my 80 meter sked. I had to back off the drive to keep it legal on
> the ham band but the MARS operators (none of the hams though the
> sergeant for the station was a ham and had made their tuning chart) were
> accustomed to seeing maybe 200 watts out. Though the plate and grid
> currents were correct for full output. I tuned it for maximum output,
> and it also had the correct plate and grid currents and a solid 2 KW on
> the Collins wattmeter. After my QSO, they wouldn't let me go back to the
> barracks without making them a new tuning chart. The next day they
> reported that the signal was so much stronger half way around the world
> that it was noticed, "So you finally got the final turned on!"
>
> 73, Jerry, K0CQ
> --
> Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> Reproduction by permission only.
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