Wondering if anyone can advise on this tube triode (12ax7) preamp stage followed by an Op Amp buffer stage to correct the inverted signal. I wired it up and did not work. Before tho, I wired it with 22K resistors instead of 220K. Perhaps signal was overloading OpAmp? Also, should the impedance output from the OpAmp be essentially the same as if it were from the triode, just inverted?
Middle 1 Meg Ohm resistor is not needed. Remove the 5000 pF capacitor from U1b (-) node.
You will have less gain than expected because the 220K input impedance of the op-amp stage is loading the output of the tube. But that's not enough to stop it from working.
What voltage are you running the tube's filament at?
There are a few things wrong here:
As noted by Dwayne Reid, the cap on the op amp's negative input needs to be removed. A cap here will prevent the op amp from operating correctly.
The circuit as shown will mostly serve to burn out the op amp. Consider the signal level at the tube's plate: it'll be around 200Vpp max. The op amp, with its +/-15V supply rails, cannot hope to invert that without clipping to those rails. When it does clip, you'll end up with at least 42Vpp at the op amp inverting input (very roughly, and very conservatively). This will damage or destroy any op amp not specifically designed to tolerate such high input voltages.
If you're truly trying to simply re-invert the tube's plate signal unchanged, however large that signal may be, you won't be able to do it with any common op amp: there's just no way to get a 200Vpp signal out of an op amp which is powered from +/-15V rails. There are high-voltage op amps available which you could use, but they are rare and expensive.
If it fits your requirements, another option is to reduce the plate signal level in one way or another such that a normal op amp can work with it. This will of course manifest as a reduction in the end-to-end gain of the circuit, but the resulting "mapping" of 200Vpp to 30Vpp may actually be the result you're looking for.
