Correction on the gird current. I mis-stated the numbers. It is 260 ma
under CW conditions and 130 ma under SSB conditions.
Data is taken from the Tentec operation manual for the Centurion.
73
Bob, K4TAX
----- Original Message -----
From: "Mike Hyder --N4NT--" <N4NT_Mike.Hyder@charter.net>
To: <tentec@contesting.com>
Sent: Thursday, August 21, 2003 6:08 PM
Subject: Re: [TenTec] AMP Question
> 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: <geraldj@isunet.net>; <tentec@contesting.com>
> Sent: Thursday, August 21, 2003 6:39 PM
> Subject: Re: [TenTec] AMP Question
>
>
> > 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.
> > > _______________________________________________
> > > TenTec mailing list
> > > TenTec@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/tentec
> > >
> >
> >
> > _______________________________________________
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>
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