I have always used John's idea of putting the HV plate transformers on one
side of the a.c. line and all the rest on the other side, with my homebrew
HF-300 rig (in which everything runs off a 115-volt primary). That way, the
voltage sag caused by the current pulled by the modulator ADDS to the
primary line voltage at filament transformers and low-voltage plate
supplies. My pilot lights actully get slightly brighter under modulation.
This is addition to the initial voltage kick-up caused by the current pulled
by the rf finals, as soon as the transmitter switches to the transmit mode.
Of course, the HV still sags normally as the power supply is loaded.
Although I have never tried it, another idea, which might help modulation
linearity with an especially poorly regulated power line, would be to run
separate modulator and rf final plate supplies, and put the rf final on one
side of the line and the modulator on the other, giving the rf final
filament and plate voltages a boost under modulation.
When my station was in the upstairs bedroom in the house, the line voltage
would vary as much as 5 volts when the transmitter kicked in full strap.
Now that my station is in a separate shack outside the house, with heavy
duty wiring running out to it, the variation is less than 2 volts.
Don k4kyv
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