heres a drawing of my modified grampian 636. parts of it mite look a bit weird. without delving back into it (where i was for ages already) i can say that it works very sweet. theres several opotunities inside the circuit for gain changing. the mic stage gain control is very strange. i might be wrong about that part.goes well tho. when the gain is low (-) not much mic amp noise gets thru to the next stage. the board is a messy one. badly planned out on variboard. my one anyway. it was a mission to draw it. all good tho. note the power supply end. im not absolutely sure ive drawn that right. i remember having issues when using a centre tapped supply. i think it went ok when i had two seperate 9v supplies – stacked. 18 volts from ground to hot. and a clean 1/2 of that fed just for the tank driver. the 2000 uf probably arent even needed if you using batteries? anyway. try some things out. have a think. youll work it out.
also note that this is a positive earth unit. good luck.any discuss about the circuit is welcome. germanium sounds so good. its all kinds of noisey but so so juicey. wow.