In order to "beef up" the 160 meter performance of the Alpha 77SX
amplifier a number of changes occurred in the upper and lower RF decks
that are pertinent to the thread.
1. The complete filament supply was originated at a separate transformer
from the Anode Supply. Said transformer was suspended above the
chassis
with 1" by 0.625" ceramic standoffs.
2. The filament supply was rectified and filtered into a D.C. supply,
with
a fully-floating Full Wave Bridge rectifier, (pro's and con's
notwithstanding,
the point is not particularly germane here.)
3. Two bifilar-wound 30 ampere filament chokes were added, one choke
per 3CPX1500A7 triode. The DC supply lines to the tube sockets were
not grounded at either polarity.
4. The 1.2mH, 500mA cathode choke on each tube was replaced with
a 1.2mH, 3 ampere choke.
5. Bypass capacitors, (.01uF/3KV) were added on the cold side of
the filament chokes, to chassis ground.
6. Two silver mica .01 caps were added on each tube socket in between
the filament attachments to equalize any RF on the tube socket pins,
per tube.
7. As an experiment, one side of the DC filament line was directly
connected
to the Cathode pin(s) on each tube. I believe this should actually
be a
silver-mica bypass capacitor, as the problem of 100mA of grid Current
appearing with the slightest amount of RF drive plagues the
amplifier.
Above the plenum, the tank circuit and other components have all been
changed to modify the output Q of the paralleled triodes, but that is not
part of the thread.
Respectfully,.
Hal Mandel
W4HBM
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