I did use the 1.8k on the resonnance path. There is much more gain on my second built, so I do suspect that the main difference comes from the overall level.
It’s National , not TI…
Yeah the test VCO circuit looks simple, give it a go after I get back from Holiday next friday.
The TL074 is pseudo-TI.
Actual logo
The NS logo on the LM13700 looks more plausible.
The 74 works in my basic tester, but it could be out of spec for the filter i guess… Its probably from a batch i have been using for the last 3 "years on most things ( or being such an old build may have been a random early purchase .
Its quite a long time since i have even looked at fixing it.
Can try a 74 from my latest batch. I think this other 13700 is fro. The same barch though.
Yeah the logo on the new batch looks much crisper and with a defined “i” so either more genuine or the fakers have a better screen printer now 
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That plus Texas actually looks like Texas, and not so much like an outstretched hand with an extended middle finger.
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I’m running the triangle/square VCO on ±12V with 100K instead of 30K on Vc and 10uF for C. Gives a nice 2.5Hz. Add an LED w resistor to the square output and you have a quick 13700 go/nogo tester.
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What do you mean by “never worked right”? If it sort of works but not really then it seems like the LM13700 is doing something, just maybe not very well. In that case just seeing if a simple oscillator oscillates might not tell you much. I guess it’s a quick simple test and if it fails there’s the problem, but if it doesn’t it still might be a dodgy though semi functional OTA.
IIRC and it’s two years ago , all it seemed to do was self oscillate. It’s not been on my mind much but I was considering a MS20 style filter as part of my own POLY6 build.
Could just be a problem with the feedback loop then… which includes the TL074. Or just an assembly fault that causes the op amp output to be too large.
realise I am thread jacking… But I guess it’s a relevant. I guess I am not even sure what I should be expecting.
A bit of testing yesterday ( was a bit random functionally but could just be dry)
should I see only High or Low ( switch dependant ) being passed with the output of the High or Low either being 0 of full… or should it be passing the full spectrum and just attenuating the High/Low. it’s doing the former more or less badly.
I can verify these don’t work. 
