Quote:
Originally Posted by Alejandro Lieber[_3_]
I am thinking in building an AM transmitter for 7.1 Mhz (40 meters) using a
EL34 in class C as final.
The idea is to modulate it by varying the negative polarity of the
suppressor grid (g3).
Suppose I load the EL34 plate with 500 volts DC and a current of 150 ma with
0 volts suppressor, does anyone have any idea what negative voltage in g3 is
needed to reduce the anode current by half, needed for screen AM modulation ?.
Alejandro Lieber LU1FCR
Rosario Argentina
Real-Time F2-Layer Critical Frequency Map:
http://1fcr.com.ar
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As the G3 voltage is biased negative the G2 current will increase in proportion to the decrease in anode current. That can result in a dangerous increase in screen dissapation. To prevent that, the screen needs to be supplied thru a limiting resistance. Refer to the attachment lifted from FE Terman.
The EL34 will easily handle your 500 volt supply, it is rated to 800 volts on the plate. But the socket is something needs to be of good insulation. As Patrick T has said, an 807 would be a better choice.
Many amatuer transmitters were built using TV horizontal output tubes which are still common. That gets around the socket insulation problem. And it better isolates the RF input circuits from the output. Less likely to have parasitic oscillations.
Cheers, John