[ARC5] FW: Way OT -- SX-28 - ARC5 selectivity

[Hubert Miller]

Some of you may be familiar with the triode first audio + bfo circuit used by Collins in the TCH
and TCS. In the same triode stage, I emphasize. When you first see it, you think it's a stunt
Ecophone might have used, but - Collins used it, maybe devised it, and - - it works ! And works
well. This is so much better than the cornball circuit raising the IF suppressor grid above ground
to make it oscillate. I think what makes it possible is that the oscillator is Class A, which is slightly
unusual in oscillator circuits. ( This is the 'secret' of how Michael Rainey's one-transistor direct
conversion receiver works too. ) Collins pipes the BFO signal from the 6SQ7 to the diode detector,
then the audio goes thru the same 6SQ7 triode. I used a TCS for a while as a complete Novice 
station and it worked fine, the IF selectivity being the only challenge. I tried both audio LC filter
and IF Q multiplier. The audio LC gave too much ringing and even at max selectivity the Q mult
was more bearable. 
-Hue Miller