On May 26, 2006, at 11:45 AM, Peter Chadwick wrote:
> 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
Since 4cx250Bs and their cousins do not have a striped cathode and
aligned grids like the 4cx1500B and 4cx600J, they are not anywhere
close to linear in grid-driven service whenever grid current flows.
Without RF-NFB, such as is the case in G-G / cathode-driven, AB2
makes some serious amounts of doo-doo.
> Peter G3RZP/W6 (this week)
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|