[AMRadio] BC-610 down=up

[Donald Chester]

>So I was half correct. But it is indeed an unbalanced system. I was
>recalling about an article done back in '94 in an issue of Electric Radio
>which stated that the final only utilized half the coil.

The final is single-ended, but the plate tank circuit is balanced just as in 
a pushpull amplifier.  This is the classic plate-neutralised triode final.  
The other half of the coil functions to generate the out-of-phase rf voltage 
required to neutralise the circuit.  True, the tube works into only half the 
coil, but the circulating current of the resonant tank circuit is present in 
the entire coil, which along with the split-stator variable tank capacitor 
make up the tuned circuit.  The Q of the tank is determined by the LC ratio 
of the entire coil and capaciter.

The circuit is inherently balanced.  The flywheel effect of the tank circuit 
takes care of the fact that the rf pulses are introduced on only one end of 
the coil.  The link output on the BC-610 came from the factory balanced, 
with two ceramic insulators at the output.  I have seen many of these 
converted to an unbalance output by grounding one side to the cabinet and 
using a SO-239.  But the link in the middle of the tank coil is inherently a 
balanced output.

Don K4KYV