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Re: [Amps] SB-220 HV Transformer Wanted ; thread stolen for

To: amps <amps@contesting.com>
Subject: Re: [Amps] SB-220 HV Transformer Wanted ; thread stolen for
From: Ron Youvan <ka4inm@gmail.com>
Reply-to: ka4inm@gmail.com
Date: Fri, 1 Nov 2019 14:04:59 -0400
List-post: <mailto:amps@contesting.com>
On 11/1/19 12:30 PM, Jim Thomson wrote:

##  when  was  the  last  time  you  saw a push-pull  class  B
RF linear amp....using tubes ??   I  saw  one  when  I  was a kid,
and  it  was not  linear.  2 x  tubes  in  P-P  is a complex mess
for  RF  HF  freqs..esp  multi  band.  They  draw  lots  idle  current.
    Same  2 x tubes in  parallel,  in  AB  for  ssb
linear  use....  or  class  C, for   CW,  FM  use is  even  more  eff.

##  GG  triodes cant  be used  In  class  B  on  CW.... u  will  get  key  clix.
A  simple PI  net  will kill  even  and  odd  harmonics.   Typ P-P  Ham  xcvr
requires  7 x LP  filters  to  kill  even +  odd  harmonics.  GG  triode  does
not  require a  LP  filter.....none.

  I cannot call 10 to 20 % idling currents lots, like .200 Amperes for a
3.0 Ampere plate current per each tube in a 25,000 Watt am modulator.

  I have seen plenty of push-pull "Class B" RF amplifiers, being a worn
out broadcast engineer.  The Raytheon Company use to make low power am
transmitters and they were superior to the common RCA and Gates units.
The 250. Watt transmitters use two RCA 810 tubes (triodes) in push-pull
"Class B" modulation amplifiers and two RCA 810 tubes in push-pull
"Class B" AF amplifiers.  For one kil-a-Watt transmitters they used two
RCA 833 (triodes) in push-pull "Class B" modulation amplifiers and  two
RCA 833 tubes in push-pull "Class B" RF amplifiers.
  In the Raytheon transmitter these tubes had a reputation of lasting
three years as the RF amplifier and when the emission was down they
moved the modulators to the RF stages and installed new tubes in the
modulator stage and got another three years.

  RCA and Gates got one year out of their parallel RF amplifiers.

  The reason we don't all use push-pull "Class B" RF amplifiers is our
propensity for multiband operation.  Before 1960 many hams had push-pull
"Class B" transmitters that used a pair of RCA 811, 812 or 813 tubes and
1 kW B&W plug-in coil sets.  (all grid driven with 100. W. B&W plug-in
coil sets.)  If there is any instability in a push-pull "Class B" RF
amplifier they are easily "cross neutralized."

  All of our "rice boxes" use a "Class B" RF amplifier" as the final
amplifier, driven by a beefie class "A" transistor.

  If you consider the amount of time the devices are idling, class "B"
amplifiers are the overall most efficient linear amplifier that there
is.  Don't think two parallel devices is the same as a push-pull "Class
B" RF amplifier.
--
   Ron  W4BIN - Understanding is much better than
                                       knowing how.
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