Careful is showing off your work @Shadetree Mechanic - you'll find yourself with a lot of buyers wanting a piece of you...
Maybe by the time I retire in 12 years, I will know enough to be able to make some pocket money by doing this. Sure beats selling firewood, which is what I used to do.
Thanks for all your help Andy. The audio with the 500k pot turned all the way up, did not sound bad or different, its just that when I was turning it up, it got to the point that turning it more didn't make it sound any louder. So it left it at that point and I would bet that it is at 330k or really close. This will be a handy adjustment to play with, after I figure out the audio limiter.There is an Upper limit to the level of amplification the thing (the 4558 chip) will produce then it's nothing but acting more and more non-linear and nearly digital - the 4558 is originally a comparator - made analog by the feedback loop you're "toying" with...
Curious to know what you felt that limit was by ear, and what that pot measured out to be?
My guess is close to that 330K - anything higher just "pinches out"
Using the schematic for the 979, it seems that the 86v has all the same parts, at least in the audio section. Going by the information you already gave me, it looks like I can make the value of R186 bigger, or put a resistor across D64. Maybe a trimmer at R186?
What you can try and see to some success is to install two resistors - one across D64 as you said, but also you might want to REDUCE the drive it detects by placing a resistor from the JUNCTION of C157 and R186 (start with 1K) with the other lead to foil board ground.
I tried two, 1k trimmers in these locations. I am having a hard time quantifying any difference. Maybe I don't have enough audio to cause any clamping action to begin with? I will go back and verify that I am on the right spots.
Yes, the "clamping" is not "clamp" but "clip" and in flattopping - "scrunch" distortion moments are more the effect.
If you had done any work to the Limiter section - this may be a moot point...
Because what you are trying to determine is if any more attenuation / limiter action is needed. Action being the Limiter - is it hitting the audio still too hard? Doesn't appear to be - you're margin seems to be more towards compression than peaking.
So if the results are little to no effect - then the circuit is balanced the best you can make it and you can just continue on.
Balanced being that the input TO the circuit and the output FROM the circuit is low enough so they any effort you're doing to make the radio "louder" this section is not causing the "squeeze".
Placing a power mic on this? IT's the only other way to check - which again, because of the work you've already performed - by observation - the limiter needs the higher output in order to have any impact - so if no true results can be heard. So the work being performed by you as you go - doesn't seem to impact as much as if it was in it's stock form.
I would like to know if you're checking this in other modes like FM and SSB?
D64, D61 and D62 are the Positive peak sensing feedback loop for the Mic Amp. When installing Ta opGun CP1, they instruct you to remove the feedback resistor and replace it with their module, and remove D61.
This is what I used to do, assuming the Mod limiter circuits (AMC/ALC) are intact: Do not remove D61 as above.
C158 is your "Sample and Hold" capacitor for where the AMC sense and ALC sense tie together, to the rest of the AMC/ALC circuit. Solder a 22k (10k?) across this capacitor. This allows the capacitor to react to, and hold on instantaneous peaks, but release a whole lot faster. The value depends on the model of radio. On RCI2950's (pre-DX), I used 10k, on 2970's, I used 22k.
On SSB, using an Oscilloscope, readjust the peaks to just under rail-to-rail, you want curves, not flat tops. Instead of a triangular sideways Christmas tree pattern, it becomes a much fatter Christmas tree pattern. On AM, same goes for that, on positive (no flat tops) and negative peaks (no gaps or 0 RF). This makes it a quasi syllabic speech compressor.