I have to admit that I have run a pair of 4CX250B's in AB2 on 144 MHz during my
SK6AB days... (late 70's)
Hopefully the limitation time for these "crimes" has long passed.
Some inspiration for the class AB2 operation came from certain articles in
UKW-Berichte by DK1OF.
The DK1OF PA design for 144 MHz quotes the following operating data for class
AB2 (one 4CX250R)
No load Ua 2200 V
Ug2 380 V
Idling Ia 100 mA
Single-tone Ia 420 mA
Drive power 8 W
Ig2 20 mA
Ig1 5 mA
Power out 520 W
(all single tone)
It can be gathered that the amplifier was operated well into
peak limitation, as the drive power was doubled (+3 dB) but the output
only increased by 1.3 dB when going from class AB1 to AB2.
For some reason the linearity was not measured...
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Peter Chadwick" <g3rzp@g3rzp.wanadoo.co.uk>
To: <amps@contesting.com>
Sent: Friday, May 26, 2006 8:45 PM
Subject: [Amps] Historical question-probably OT
> At Dayton, I got a 1960 ARRL Handbook ( got to update the station!) for my
> collection. It has an interesting HF amplifier in it, using a pair of 4X250,
> (NOT 4CX) running, it is claimed AB2 passive grid, although the drive level
> discussed seems to me too low for AB2. It is enough for AB1, though. Some
> other interesting historical features are the power supply, which used
> germanium rectifiers. A transformer with two 325 volt windings, each voltage
> doubled and wired in series, and no bias regulation, which again makes me
> query the AB2. Also, a fixed link coupled output network, pretty well
> necessitating a tuner - shades of today's solid state stuff!
> Another point of interest is the modification of the tube sockets to reduce
> the back pressure so that a big axial fan can be used for tuning. The design
> was published in a 1958 QST. Has anyone here ever heard of any of the 250
> series being run for linear amp service in AB2? I've only ever seen AB1
> discussed.
> 73
> Peter G3RZP/W6 (this week)
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