[AMRadio] BC-610 Modulation Transformer

Donald Chester k4kyv at hotmail.com
Thu May 25 00:10:10 EDT 2006

>From: "crawfish" <crawfish at surfmore.net>

>I was given a BC-610 modulation transformer this past weekend at Dayton, 
>and need specs on it. I know the -610 used 100TH's, but have other 
>tubes(HK254, 4-125's, 813's). Trying to find portion of the TM on the 
>BC-610 that has the schematic.

It's about 20K plate-to-plate primary to 8K secondary.  The 610 runs 2000 
volts at 250 mills to the final, making the modulating impedance 8000 ohms.  
The turns ratio is abot 1.65:1, so the impedance ratio is just under 3:1.  
The transformer should be useful for any class-C load impedance between 
about 5K and  12k, provided the DC through the secondary doesn't exceed 300 
mills or so.  Naturally the 3X load impedance will be reflected back to the 
modulator tubes.

Using a common power supply for modulator and final, with this transformer 
don't expect to get much over 100% positive peak modulation capability, 
because of the stepdown ratio.  For higher positive peaks you will have to 
run higher voltage on the modulator than on the final.

Don k4kyv

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