Info needed for Heath IG-18A/SG-18A audio generator

[Robert Groh]

In the process of working on radio's again, I am doing some badly needed tuning up, dusting off, calibration and general fixing up of my test equipment. So I dusted off my SG-18A audio generator. I found several resources on the web which gave me a copy of the schematic plus several sites with improvements for the -18.  

One remaining 'nit' for me is the 'wagging' of the meter. The amplitude reading on the output meter and, indeed, the output itself is apparently being modulated at a period of about 250 mS.  This is also reflected in the square wave output in that the duty cycle is also varying (not too surprising).  

So anyone seen this before and does anyone have any suggestions.  I've lived with this for a bunch of years and now finally getting to it!

73
Bob Groh, WA2CKY

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