Vacuum Tube Op-Amp schematics

[Don Symes]

By way of Bob Pease's (renowned analog wizard) site, I found some datasheets and schematics for Vacuum Tube Op-Amps using just a pair of 12AX7 tubes. The downside is that they want +/300V supplies, but for an opportunity to try a BiQuad filter set or a tube-synthetic-inductor-EQ, it might be kinda cool.

[Enzo]

Bob Pease is great. If there is such a thing as an electronics hero, he's mine. His book, Troubleshooting Analog Circuits is one of my favorites. Every time I read it I learn more stuff. He talks about those old op amps often in his column in Electronic Design.

[Steve Conner]

Whee, I love that book! Have you seen my tube parametric EQ circuit? http://www.scopeboy.com/peq.html

I used op-amps for the "synthetic inductors" (actually state variable filters similar to biquads) but I arranged it so all the gain and any clipping happens in the tube stages.