Also, I replaced the mod reactor with a potted unit.
The original one talked back so badly that I could just barely crack the
mic
gain before it started accoustical feedback.
That bothers me... maybe they are not all the same. Mod reactors are
hard to find, especially potted, sealed ones. I do have a spare RCA
reactor, 60hy @ 650ma, but it's open frame too.
I have one of those RCA reactors too. It doesn't talk back, but it wouldn't
fit into the space of the original reactor. I swapped positions for the mod
reactor, and removed the 8005 fil xfmr since mine also uses solid state
rectifier replacements. That left just enough room for the new mod reactor,
which has a footprint of about 1 square foot. You might do the same, but
you would probably have to mount the reactor on its end, possibly making
some kind of side bracket. That RCA reactor would be just right. My potted
job is 50 henries at 600 mills.
I modified the cooling fan
circuit to run them at half voltage.
I just moved the wire for the cooling fan over to the 110 volt tap on the
primary of the 833A filament transformer. Simple as that. The fans still
run, but quietly enough that I can barely hear them. That tap was put there
to make 110 volts available if needed. Actually I have an on/off switch on
mine, so I can cut the fans entirely off if need be.
To get better positive peaks, I use a big wirewound fixed power resistor in
place of the motor controlled variable resistor used to control power. It
is made up of two resistors in parallel, total 800 ohms @ 400 watts. I use
it to drop the plate voltage to the final down to about 2000 volts, but keep
the full 2600 volts on the 833A's. I completely removed that giant
rheostat. The new dropping resistor is in series with the low side of the
modulation reactor. To protect the mod xfmr, I mounted it on ceramic
standoffs and installed a spark gap across the primary winding P-P taps. I
used the variable spark gaps salvaged from a defunct 1:1 ratio RCA mod xfmr
I had been kicking around.
Don k4kyv
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