[AMRadio] Re: WRL Globe King 500C rebuild

Donald Chester k4kyv at hotmail.com
Fri Jul 7 02:27:16 EDT 2006

In the stock transmitter, the final amplifier plate voltage is 1800 volts, 
so the 2000 volts shouldn't cause too much of a problem.  The modulator 
originally ran only 1200 volts on the plates of a pair of 811A's, and the 
modulation transformer was just barely step-down, with a turns ratio of 
something like 1.15:1.  Even so,  the modulator would just barely make about 
85% modulation in most transmitters, if you were lucky.

Running 2 kv on both with a common power supply should give better 
modulation, but the final tank cap might arc over on modulation peaks.  This 
is assuming that the G-C driver stage is capable of fully driving the 
modulator at the increased plate voltage.  With a common power supply, the 
modulation transformer should have turns ratio of about 1.4 or 1.5 to 1.  
The 572B's MIGHT work OK with the stock audio  driver and mod transformer.

Don k4kyv

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