Good morning folks.

I'm looking for detailed circuit descriptions for both relative pitch and 
null-producing auditory chopper circuits for obtaining precise readings of 
analog meters. The summaries as appeared in recent issues of QST are 
insufficient except for the unit used with the MFJ 209 antenna analyzer. 
Optimally, I could get my hands on the descriptions that appeared in Bob 
Gunderson's Braille Technical Press that were first published in the middle 
and late 1960's. I would be pleased to purchase the entire collection or 
parts thereof if anyone cares to part with them. Alternatively, I would be 
very pleased to get detailed descriptions for the two above-mentioned 
devices if anyone would care to forward them to me.

Thanks much for any help here.

Jerry  VE3QSO