Not being real versed in circuit theory, I was wondering if someone can explain what is going on in part of a circuit I was tracing out today. It's basically a 1950's 2-tube phono circuit---12SQ7 preamp,50L6 o/p with a silicon rect. My question is --the 12SQ7 has a .02 cap to the grid (input signal from vol. ctl), no other connection...Then, they ran a 2.2 meg res. from the grid of the 12SQ7 to the grid of the 50L6, which already has a 470k grid res.to ground and, a .03 cap from the plate of the 12SQ7. I've never seen that arrangement of grid to grid..if I dis-connect the 2.2 meg, it goes into feedback squeel. The circuit works as-is fine...just want to know what is happening technically here, to build my knowledge base.

Brian

Negative feedback. Normally a grid resistor would go to ground. By connecting it to grid of the next stage a negative signal is taken from grid of 50L6 and fed back to grid of 12SQ7. Since it's out of phase cancels some gain.

Norm

:Not being real versed in circuit theory, I was wondering if someone can explain what is going on in part of a circuit I was tracing out today. It's basically a 1950's 2-tube phono circuit---12SQ7 preamp,50L6 o/p with a silicon rect. My question is --the 12SQ7 has a .02 cap to the grid (input signal from vol. ctl), no other connection...Then, they ran a 2.2 meg res. from the grid of the 12SQ7 to the grid of the 50L6, which already has a 470k grid res.to ground and, a .03 cap from the plate of the 12SQ7. I've never seen that arrangement of grid to grid..if I dis-connect the 2.2 meg, it goes into feedback squeel. The circuit works as-is fine...just want to know what is happening technically here, to build my knowledge base.
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Thanks Norm, makes sense now.