Ian,
You wrote,
>
> Therefore if you tune up at full power and then reduce the drive without
> touching the output network again, you're simply driving the operating
> point a smaller distance along the *same* load line. The load line
> itself doesn't move, so I don't think the loaded Q of the output network
> changes with drive level either.
I always notice a difference in tuning for for a given maximum at any
particular level.
Normally, when I tune my 3K Premier with 10-20 watts drive for maximum power
at this level, inevitably there will be a slight retune needed at full 100
watts drive.
Looking at your last statement, what's different? Is it the small plate
voltage drop causing a different plate load impedance at the full drive
level that makes for the change in tuning?
73, Dan Magro W7RF, (member SCDXC, SCCC)
Rugged, Reliable Henry HF Amps are "Instant on" for RF Power now!
DXers/Contesters/Ragchewers get your HENRY from RADIODAN for LESS!
***Subscribe to the HENRY reflector at www.qth.net <http://www.qth.net>
***
www.radiodan.com <http://www.radiodan.com> ??? RFpower@radiodan.com
<mailto:RFpower@radiodan.com> A trip to our web site is worth the click!
> -----Original Message-----
> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
> Behalf Of Ian White, G3SEK
> Sent: Tuesday, December 08, 1998 2:16 PM
> To: amps@contesting.com
> Subject: [AMPS] Henry 8K at 1500 watts Out -- Warning Long
>
>
>
> Jim Reid wrote:
> >
> >Jim, KH7M wrote, in part:
> >
> >>>In fact, with 100 watts into the 8K, and it's 13 dB gain, you will
> >>>get out around 2000 watts, so better cut the drive in back until
> >>>the Bird in the 8K reads no more than 1500 out with the key down,
> >>>SSB peaks.
> >
> >
> >Rich, AG6K responded:
> >
> >>However, the tank of the Henry 8k is designed for a much lower RL --
> >>i.e., the tank is designed for 2.5a of anode current. In order to
> >>produce this much anode current, c. 400w of drive is needed.
> >>>......
> >
> >And, presumably under this plate current, the QL, the
> >loaded Q of the tank will be something above 10, or so.
> >
> >
> >However, Rich has caused me to revert to Terman, hi.
> [...]
> >So, I see no harm to the 8K in operating it at low drive,
> >and constraining it's power output to legal limits, where
> >it evidently provides very linear operation; but at the
> >cost of probably very poor efficiency.
>
> Another way of looking at it is that the purpose of the tank circuit is
> to create a load line for the tube. It does that by transforming the 50
> ohm load impedance "backwards" up to typically a few k-ohms.
>
> As seen on the tube characteristic curves, the effect of the RF drive is
> to move the instanteneous operating point back and forth along the load
> line, once every RF cycle.
>
> Therefore if you tune up at full power and then reduce the drive without
> touching the output network again, you're simply driving the operating
> point a smaller distance along the *same* load line. The load line
> itself doesn't move, so I don't think the loaded Q of the output network
> changes with drive level either.
>
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.demon.co.uk/g3sek
>
> --
> FAQ on WWW: http://www.contesting.com/ampfaq.html
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
>
>
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|