[AMRadio] : BC 610 needing POWER 220VAC

Donald Chester k4kyv at hotmail.com
Sat Apr 8 14:30:23 EDT 2006

>From: Rick Brashear <rickbras at airmail.net>

>Well, Brian, you are right, the 11 ohm dropping resistor is only in series 
>with the plate transformer... Of course, you're also right as is Jim that 
>this would throw the modulation bias off... As indicated earlier, it's easy 
>enough to operate with lower power by simply adjusting the coupling.  I say 
>"easier" sometimes that rascal can be real touchy.

It's best to run the BC-610 in the full power mode.  HV protect is for 
tuning up without risking damage to the final tube or other components.  
Running the rig in HV protect will result in very poor voltage regulation on 
the final, due to the series dropping resistor in the HV xfmr primary.  
Running it with reduced loading will throw the load impedance to the 
modulation transformer way off, with the possibility of blowing the xfmr or 
arcing something over in the final.

The only proper way to reduce power would be to operate the plate 
transformer from a variac or some other kind of autotransformer, to provide 
a well-regulated source of reduced a.c. line voltage.  Then the modulator 
bias would have to be reduced, but that would require extensive 
modifications, due to the combined audio driver plate/modulator bias power 
supply arrangement.

Best to just run the BC-610 according to the stock instructions in the 
manual, if you are not confident about doing extensive modifications to the 

Don k4kyv


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