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"tuning" signal generator.

Gabriel E.
"tuning" signal generator.
Just picked up a Heathkit tube signal generator from the late 50s/early 60s at a thrift store.  
It works! However the tones it generates are slightly off key. 440 hz comes out as Ab- instead of A.  
Not a big deal but I'd like to know if it's possible to tune this sucker to make it more accurate.
Mark Lavelle
If you open it up you might find a trim pot inside...  
Failing that, a schematic is pretty much necessary.

Or loosen the set screw and move the knob. These are not lab standards, they are only designed to be close. Even if you set 440 indicated to 440 actual, the thing still may not track up the scale, so 1000 may wind up 990 even if 440 is dead on.  
ANalog synths used to adjust for not only pitch but scale as well. Get the octaves really an octave apart, then set the tuning.  
If the thing has a relatively large variable air capacitor - lots of fins on a shaft - as the main tuning component, there is often a small trimmer mounted right on it. Trimmers were small square things with a screw in the center of the flat area.
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