I don't believe you have sufficient grid current. The grids of 3-500z tubes
when the tube is cathode driven normally draw 108 mAdc each. That is 216
mAdc for a pair. Where did the 130 ma red line come from?
If you like, I can email Eimac 3-500 data sheets direct to you.
73, Mike N4NT
----- Original Message -----
From: "Robert & Linda McGraw K4TAX" <RMcGraw@blomand.net>
To: <email@example.com>; <firstname.lastname@example.org>
Sent: Thursday, August 21, 2003 6:39 PM
Subject: Re: [TenTec] AMP Question
> 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
> 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
> 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 @
> 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
> point in tuning without overdrive.
> Just curious why the tubes show a good bit more color on 40 M than on 75
> 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
> on any of the other bands except 160M and 75M.
> Bob, K4TAX
> ----- Original Message -----
> From: "Dr Gerald N Johnson electrical engineer" <email@example.com>
> To: <firstname.lastname@example.org>
> 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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