[AMPS] Re: 812

[Paul and Abbi Elliott]

In the late 1930's and the early 1940's a very common transmitter line-up
was a pair of 812's modulated by a pair of 811's.  If the amplifier and the
modulator were powered by a power supply of 1250 volts or less, the 811's
could be run with zero bias.  Although both tubes were rated for both audio
and RF service,  the 812 was used essentially only in class C rf
applications and the 811 was used only a a class B modulator (in amateur
ranks).  

On page 162 of the 1941 ARRL Radio Amateur's Handbook, the caption of Fig.
1032 reads, in part:  A 450-watt push-pull amplifier of dish-type
construction suitable for 812's, T55's, 35T's, 808's, RK51's, HY51's,
HK154's or other tubes of similar style operating at plate voltages of 1000
to 1500. ---

With the advent of SSB and the need for linear amplification, the 811 came
into its own in RF service.  The September-October 1952 issue of "GE Ham
News" described the "Power Peaker" using a single 811 in a grounded
cathode, so called "grid-neutralized", circuit running class B.  A driving
power of 2.5 watts gave 200 watts output with 1500 volts on the plate (just
don't whistle too long or too loud into the mike!)

I built and operated an amplifier that copied the electrical circuit but
differed completely in physical layout.  I operated this amp, using a 1250
volt supply, on 10 and 20 meters.

To add a small note to the parasitic suppression information, the only
parasitic suppression element in the amplifier was a single 10 ohm resistor
connected between the grid terminal on the tube socket and the grid tuned
circuit.  The plate current with no driving power applied was about 30 to
40 ma.  Loaded, or inloaded, regardless of the settings of the grid and
plate tuning capacitors, the amplifier never exhibited and tendency to
oscillate.  

73

Paul W5DM

--
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