[AMRadio] Transformers Revised

Rick Brashear rickbras at airmail.net
Tue Feb 20 17:31:00 EST 2007

It's been a while since I fiddled with the 610-E, but it seems I 
remember they had all 115 vac primaries instead of the 100 volts as does 
GE.  I could be wrong, I'd have to pull the schematic.


D. Chester wrote:

> 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.
> 73,
> Don k4kyv

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