[AMRadio] Transformers Revised

D. Chester k4kyv at charter.net
Tue Feb 20 17:23:48 EST 2007

The idea is to be able to compensate for low line voltage.  The filament 
xfmrs are fed from the 115 volt line through a rheostat to 100 volt primary. 
In case of  low line voltage just decrease the resistance in the rheostat 
and you can bring filament voltage, which is somewhat critical with 
thoriated tungsten filaments, up to the nominal value with line voltages as 
low as 100 volts.  If the line voltage is higher that 100v, just add 
resistance in the line and bring it back down to 100v, which furnishes the 
correct filament voltage to the tubes.

This is fairly common practice with many transmitters.  The BC-610E has the 
same arrangement.

If you can't find the correct transformer, the primary could be wired in 
ahead of the rheostat directly to the a.c. mains voltage, but you will lose 
the variable filament voltage control for that tube.


Don k4kyv 

More information about the AMRadio mailing list

This page last updated 16 Dec 2017.