[AMRadio] info wanted on 4-400 linear amplifier

James M. Walker chejmw at acsu.buffalo.edu
Wed Aug 3 23:04:00 EDT 2005

Actually, it was 20 - 30 RF volts. Grid drive is around 5 MA. I use mine
with a Pacemaker driver, and a 20 DB ~ pad inline and the connecting
is prescribed to be 60 inches long to prevent parasitics.

The thunderbolt can also be driven directly by an (un)modified Central
Electronics 20A, or the CE 10B, I use both of them from time to time. In
SSB mode, you really need to watch the audio levels and monitor the RF
output waveform, however I found that when running AM from the CE rigs
you really have to be careful not to bang the audio as well as the
goes right along and you end up with a higher carrier level and lower
read (muddled) audio.

The 1962 ARRL handbook has a single 4-400A amplifier, which I think is
the original question, I built one in the 1980s I had no problems with
it, and I redesigned the output to use vacuum variables and a roller
inductor instead of all the thrashing around with jumpers. It worked
quite well, and I still had to reduced the drive level to keep it in
limits for the tube. With 3KV on the plate it is quite handy for rtty
and cw, the AM was handled by lifting the modulator circuit from a
t-368 schematic, worked quite well.

Patrick Jankowiak wrote:
> The Thunderbolt was easily driven to full input by 20 watts. I
> recall it was easy to tune and very sensitive due to grid drive.
> The grid was swamped as I recall, so it was also very stable.
> PJ
> --
> the Johnson Thunderbolt is a AB2  amp that uses 4-400A's check
> out this amp
> i think you might like the layout it uses a roller inductor
> instead of a
> varicap.
> 73 Tony wa4jqs
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