Grant 999AD AMC/ALC Problems

[MKwrench]

I think I know where the problem might be, but thought it would be cool to share as I undo a few audio cap changes that I thought would "open up" the audio a little more.
The issue is with the ALC and AMC adding weird distortion and oscillation that will continue without any added audio while keyed.
I made two quick videos to display the problem.
At some point I changed C207 and C211, both were 473 Mylar that I swapped for 104s and C146 that was a .22 tantalum for a 2.2 tantalum. I don't remember if I swapped C212 with a 220 from 100
These swaps were done while I was in the radio because one of the 2SC2312s getting hot from its bias pot going open. I tossed one final, swapped both with HG 2312s, along with R253, R254 (one didn't look happy anymore) and the final bias pots. I don't know how important it is to keep things equal between the two, but I tried my best to do just that.
I'll show the changes after removing my "audio experiment" caps tomorrow morning, if I get the chance.
Some of the other caps were swapped out to beef up filtering and power, others just because of bad experiences with the 10v rating.
I had some other questions about the ASC, which looks like it was added on and just flopping around inside (maybe another post).
The schematic I have is for the older PC999 (O/G) Grant. If anyone has the Grant Classic schematic, it would be super cool if you could share it.
Enjoy the videos of my sloppy homeboy workstation and feel free to offer any critique, advice, suggestions or encouragement.

 

[MKwrench]

Okay.... Who did this???
Ohh $#!7! It was me ...... Whoops!Yep that's backwards
As soon as it was corrected, everything went smooth as butter.
Thanks for not cursing me out for trying stupid mods on this radio (on my post anyhow) ...lol
Here's some more pics and video.

 

[MKwrench]

I had mentioned above that I added an "NPC" mod at an earlier point.
My notes on this radio were that replacing the 560ohm R282 with a 1K with a 4148 and 220ohm in series, parallel to it, works awesome.
I don't "volt" the finals, I never find much to gain in it unless it has a MOSFET driver and finals (they work differently), Let the 2312s sing!!!
The NPC mod will hurt the already limited FM power on this radio (mine was limited by the AM carrier level). I add an "FM Power" adjustment on the trace side. (see pic) I use a VR and a 4148 from a trace that gets voltage in FM only to the "AM Power" VR output. The VR might not be needed, but the diode is probably a good idea.

 

[TM86]

Okay.... Who did this???
Ohh $#!7! It was me ...... Whoops!View attachment 73302Yep that's backwards
As soon as it was corrected, everything went smooth as butter.
Thanks for not cursing me out for trying stupid mods on this radio (on my post anyhow) ...lol
Here's some more pics and video.

I've installed caps backwards on more than one occasion. I even installed a transistor backwards and trying to figure out what I'd done wrong drove me to set the radio aside for three years before I finally just looked at it, realized what I'd done, and fixed the problem. And I did a mod that worked on one radio and wouldn't work on the same make and model when I went to document it here.

So, no, not going to bitch at you for getting something wrong while trying to do something new. If the next guy who wants to try it sees your post and then puts the cap in the right way, I'd call that a win.

 

[711]

My $.02 which don’t amount to much is doing an NPC mod the AMC is already disabled. I put the ownership on the operator and their use of the mic gain knob. You do have an anomaly in the AMC path causing oscillation which at this point is above my pay grade maybe Andy could do one of his thorough circuit analysis breakdowns of this portion of the radio. For what it’s worth the signal looks clean and should sound pretty good.