Heath IG-18 converted to state-variable design

[richiem]

Hi folks -- I just received a replacement for my dead digicam, so I took some pix of my project to convert an IG-18 to Bob Cordell's state-variable oscillator design. Performance is very good, bordering on great. Here's the URL:

IG-18 #2

Best,
Dick Moore

 

[Ernie Milko]

Nice work, Mr. Moore.
I love my IG18, and a path like this is something I've been considering for some time.

 

[richiem]

Thx, Ernie -- another path I'll look at sometime relatively soon is increasing the capacitor ratio in the Bridged-T in the IG-18. It's 10:1 stock, but I think a few easy changes could let it be higher, say 34:1, which would raise the filter Q significantly and steepen the slope of the phase change through zero degrees, which should lower distortion and increase stability. HP uses a ratio of 100:1 in the 239A/339A, but the IG-18's amplifier won't go that far without serious mods.

 

[richiem]

I've updated the web page on the Cordell SV oscillator built into the IG-18 -- added some high-resolution spectra of the distortion performance -- it is just excellent. See the page:
IG-18 #2, the BIG-18