Again thanks to all for their help and opinions about my questions. After
reading all of your info, I have decided to stick with the power supply as
designed except to replace the original 8mfd oil with a 24mfd oil or
plastic at about 3kv. I will also replace the 350 ohm swamping resistor
with a 50 ohm device at about 100 watts to match the new rigs. I think that
if I understand what was said here, I should add cathode resistors to the
4-400's although Im not sure what value they should be. Perhaps u could
recommend the correct value. The following is a quote from the T'bold
manual for proper tuning. Keep in mind that I will be using a new exciter
to drive the amp, not the old stuff it was designed to be driven by.
"The SSB exciter should be loaded to rated input when it is used to
drive a linear amp in order that the inherent signal to noise and
suppression characteristics be fully realized. (note: I think they are
talking about the old phasing type of SSB generation). This requires an
attenuator or "swamping " load to absorb excessive power when the exciter
produces more output than needed to drive the linear amp. The Thunderbolt
operates in Class AB1 (zero grid current) up to a PEP input of 1400 watts
and is driven into the grid current region, Class AB2, to obtain the
maximum rated power of 2000 watts. When grid current starts to flow, the
Thunderbolt grid impedance drops thus presenting a variable load to the
exciter. The exciter should be heavily loaded so that the changing grid
load has relatively little effect upon the exciter. (This may be a problem
for my IC746). "
As u can see, this amp is NOT a "tune for max" appliance, but most of u
already know that! Will changing the swamping resistor have any affect on
the above quoted procedure? I dont think so but I had to ask. I think
adding cathode resistors probably will......and that is another question I
have for the list.
Thanks again,
Bill Russell
KC2IFR
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