Superior Instruments 660-A signal generator

[DavGoodlin]

Does anyone have a schematic for this unit or a working example? There's three tubes. One looks like a 6CB6 but has only a 6-digit number stamped on its shoulder "6B1000", a 6C4 and a JAN-CNU 7193, octal triode with two top caps - one plate, one grid tied together and funtioning as the rectifier.

See link for photo http://www.ebay.com/itm/Superior-Ins...-/300807987985

It works OK but does not modulate a tone onto the output. I see two transistors in the audio output circuit, one of which broke off its leads. The transistors are Raytheon CK721, an early PNP-germanium type. I can replace them with ECG-102s and see what happens, but they were added later by the looks..