Hey All

does anybody have the old schematic for the microwave modulator pcb that used the LM741 op amp and BYF51 or equiv transistor?

Im sure it was on this forum but I cant find it

You really don't want to use a 741 - they're horribly noisy! That's the basic circuit I used to use. It's a good idea to connect 100n caps from the LM317 input to ground and output to ground. It helps with stability. The '317 needs a heatsink (which has to be isolated). I used to build them in little Eddystone diecast boxes, with the '317 bolted to the case (with an insulation kit). It's a good idea to use a phono socket for the audio and something like a BNC for the output - so that idiots can't plug them in back-to-front!

I used to use either a LF351, TL071, or similar (don't think I ever used a 741 in that application, it's not something I ever had knocking around), with an emitter follower - often a BFY51. I did it that way of my own accord (current dumping onto the emitter follower, which provided the current to drive the Gunn), but others may well have come up with very similar (it's a pretty basic concept). Pre-emphasis was incorporated into the feedback loop of the op-amp; where used without an encoder etc. Modulating a LM317 is probably a more widely used approach, and well proven.