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Old December 18th 12, 07:47 AM posted to rec.radio.amateur.boatanchors
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Default Geloso G.222 TR help

Edmund H. Ramm wrote:

I found in the technical bullettin n.83 the schematic and alignment
instructions. The first thing I noticed is the G1 of 6146 is supposed
to be at -85V in CW tx. How is that possible since the only negative
supply in this transmitter is -50V? I infact measured -50V when in CW mode,
but I didn't key the transmitter as the 8289 died before I could try.


Those -50V you measured are the protective bias. When excited, the
resulting grid current will add to the protective bias.


ah that's why... It's working in C class with G1 current! I would never
expect an AM TX final amplifier to work in something else than A or B class.
Thanks for the hint. Do you know if this protective bias should be present
also when the G.222 is operated in AM position?

Tnx,
73 Frank IZ8DWF
 
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