Gentlemen,
This could probably also be done using 4 x 4CX250 or similar tubes in parallel.
The Swedish ITT Marine subsidiary, Standard Radio & Telefon AB, manufactured
for decades the ST1200/ST1400/ST1600 family of shipboard transmitters. Later
production of the ST1600/ST1680 used a 20 W class A solid-state drive module to
drive the tube PA
with 4 x 4CX250B in a neutralized AB1 circuit with RF negative feedback, to
obtain a "decent" IMD even at full PEP (1500W)
I have not heard an ST1600/ST1680 on the air for ages, but recall that IMD
measurements usually were in the -30 to -34 dB region from each tone, and the
adjacent channel noise power ratio usually measured in the -45 dB region when
driven to 1500W PEP.
An used ST1600 or its Debeg or Mackay equivalent, or the S.P.Radio (Sailor)
T-1127
that used 8122's in parallel, should not be too difficult to find after the
abolishment of shipboard Morse.
Removing some of the grid swamping would probably reduce the drive requirements
to
the FT-817 class even without using the drive module, but I find it somewhat
odd to use a 200 kg "afterburner" with a pocket-size rig...
73/
Karl-Arne Markstrom
SM0AOM
==================
Senior Radio Engineer
Maritime Networks
Telia Mobile AB
Nacka Strand
Sweden
Phone +46-8-6017171
Fax +46-8-6017957
Mobile +46-706-636575
|