Audio derived S-meter

[KC2TAU]

I've been thinking about homebrewing an audio derived (read: line out) S-meter for some of my portable receivers. After studying some circuits I have come to the conclusion that these would only be useful in SSB as considering how they are audio derived they are unable to detect or follow a carrier. Would the only way to do such a thing be to derive the signal from the AGC stage or is there a workaround to this?

[N2DTS]

I use a circuit (tube) out of a Bill Orr handbook I think, off the agc.
Its no load so its easy.
I know they have audio derived agc for cw and maybe ssb, but not for AM that I know of.
With just carrier, you are not going to get any action.
You might be able to get some meter action putting it in the cathode of one tube or another, or reading emitter current.
 

[W1RKW]

with a DC receiver you could simply tap just before the detector and design your own detector for the s-meter. If a superhet, do the same just after one of the IF stages.  You'll need to buffer (buffer amp) where you tap so not to affect the performance of the receiver.