[Collins] Self balancing audio phase inverter circuit

Jim Brannigan [email protected]
Wed, 20 Feb 2002 08:57:24 -0500


David,
I can't help you with the audio problem, but I did want to praise your
efforts in perpetuating Ham Radios lost art "Homebrewing".
I hope the radio sounds as good as it looks.......
73, Jim


> I'm working on a homebrew AM TX, 4-125's modulating a 4-400. Check out my
website for more info. (http://home.san.rr.com/km5tz/km5tz.htm)
>
> I have just about finished building the modulator and I started checking
it out today.
>
> Hum was the first problem, solved by grounding the metal cased mic amp
tube.
>
> The 4-125's are driven by a pair of 6SJ7's in a standard ARRL handbook
'self balancing phase inverter' circuit. The output of the 6SJ7 in the main
signal path looks fine but the phase inverted output from the other 6SJ7 is
not so linear. The lower half of it's waveform appears compressed and the
upper half expanded. I tried swapping tubes but that made no difference. The
4-125's are out of the circuit. All bias voltages look correct. Anybody have
experience with this circuit? suggestions?
>
> Thanks.
>
> David
> KM5TZ