PC122 AM output clipping?

[MKwrench]

I'll try to keep it short. Uniden PC122
I tried a diode in series with R186 to lower the AM deadkey to use with a small amp. On the meter It worked great, with 1W deadkey, 9W Avg/18W PEP. On the scope I can remove all negitive carrier pinch but, even with the limiter all the way up I still have flat tops at the peaks, like Frankensteins Monsters head, it looks like there could be another 50% missing.
I can get rid of the flat tops by putting a resistor in parallel across the added diode resistor pair and lowering the AM power pot more, to make a beautiful scope pattern. This Raises the dead key a bit, lowers the average wattage and the 18 PEP stays the same and I lose a good chunk of envelope growth on the scope, that I'd like to keep for good volume after the amp (Just shy of 100% now).
My question, Is it possible to add the missing PEP to Frankensteins head to round it out, or should I stick with the "extra" resistor because 18 PEP is a sort of hard limit?
It doesn't sound terrible either way, but I know that kind of stuff has to show up as an issue *somewhere*, and that added PEP would be really cool!!!
If anyone has a heatsink mod for these they"d like to share, I'm sure we would all be greatful.
Ill try to add some scope picturess and/or videos after work tomorrow evening.
This schematic is the same even though it's for a Realistic 465.

 

[MKwrench]

New video by marty kuppek

photos.app.goo.gl

 

[MKwrench]

I'll try to keep it short. Uniden PC122
I tried a diode in series with R186 to lower the AM deadkey to use with a small amp. On the meter It worked great, with 1W deadkey, 9W Avg/18W PEP. On the scope I can remove all negitive carrier pinch but, even with the limiter all the way up I still have flat tops at the peaks, like Frankensteins Monsters head, it looks like there could be another 50% missing.
I can get rid of the flat tops by putting a resistor in parallel across the added diode resistor pair and lowering the AM power pot more, to make a beautiful scope pattern. This Raises the dead key a bit, lowers the average wattage and the 18 PEP stays the same and I lose a good chunk of envelope growth on the scope, that I'd like to keep for good volume after the amp (Just shy of 100% now).
My question, Is it possible to add the missing PEP to Frankensteins head to round it out, or should I stick with the "extra" resistor because 18 PEP is a sort of hard limit?
It doesn't sound terrible either way, but I know that kind of stuff has to show up as an issue *somewhere*, and that added PEP would be really cool!!!
If anyone has a heatsink mod for these they"d like to share, I'm sure we would all be greatful.
Ill try to add some scope picturess and/or videos after work tomorrow evening.
This schematic is the same even though it's for a Realistic 465.

 

[MKwrench]

Here is with a 33K across the diode resistor combo, now I can fix Frankensteins head, but it it's weird and chunky looking through the cheap amp. Here's some video.
View attachment PXL_20240902_113717883.mp4
View attachment PXL_20240902_113025478.mp4

 

[MKwrench]

I get most of my radios in non working condition, with blown traces, other weird mods, shorted caps, missing parts, smoked transistors and/or mystery issues.
This one was full of bad solder joints, melted L26 top with missing core, and had a weird talkback mod along with some blown traces. The hardest solder joint failures to find were in the L13 / D19 area, the only reason I focused there, was because of a high VCO voltage that wouldn't chill out. It got kind of ugly inside after reworking the solder side a few times.
I went ahead with a recap along with some Goldfinger style audio mods, Clarifier unlock and my "Swingaroo" diode/resistor mod, that I can see by all the responses I got, nobody really cares for.... Lol.
I'm tuning up the RX/TX right now, I hope to test it in the truck later today.
Also.
If anyone has a PC122 (or PC122XL inner) faceplate, let me know, this one has a weird meter face that covers the LEDs.
Either way, have a great day, and enjoy!!!

 

[711]

Andy is the guru and has a huge write up on the PC122 series of radios and thought he was going to chime in. The modulation area is the same as the darlington schemes in the Galaxy/Ranger type radios. Your R186 would be the place to apply the diode/resistor NPC mod at . I never focus on the pep part and moreso on the negative and positive peaks of the waveform. Any of these NPC mods can be driven into clipping if pushed enough. I go for setting the carrier to where my negatives won’t pinch and control the positives with my mic gain if you defeat the AMC circuit. 33k sounds a little high for the resistor value but if it flies try it out. Maybe sp5it will add his expert two sentence analysis from across the pond

 

[MKwrench]

Andy is the guru and has a huge write up on the PC122 series of radios and thought he was going to chime in. The modulation area is the same as the darlington schemes in the Galaxy/Ranger type radios. Your R186 would be the place to apply the diode/resistor NPC mod at . I never focus on the pep part and moreso on the negative and positive peaks of the waveform. Any of these NPC mods can be driven into clipping if pushed enough. I go for setting the carrier to where my negatives won’t pinch and control the positives with my mic gain if you defeat the AMC circuit. 33k sounds a little high for the resistor value but if it flies try it out. Maybe sp5it will add his expert two sentence analysis from across the pond

33K was way too much, I ended up with a 10K in there, I tweeked between AM power who gave me the max and dead key, and the limiter who corrected the clipping, there were a trade off between the two. I ended up with a 3/4W carrier and a nice clean 16W PEP and plenty of growth even after the RM203 amp. (10W to 100W PEP now).
You mentioned Andy, I used a clearifier mod from one of his posts in three PC122XLs. It can be seen in one of my pics above. Those posts are stacked full of valuable information and inspiration for "Noobs" like me.
I also ended up swapping out R151 and R152 with 10k, because the limiter bit down real hard on the letter "P" when using my 636L. (which sucks because my AM handle is "Popper"....LOL), long enough to delete a whole word, but it also seemed open up the top of Frankensteins head a tiny bit too, helping my cause.
I kind of answered my own original question by looking at the final Transistor specs. Its a 17W transistor, and I'm not getting wine from a stone...lol.
After a little tinkering, I'm real happy with how it came out.

 

[brandon7861]

I hope HandyAndy don't mind me sharing this. I messaged him here a few days ago about these files, also inquired about the yellow dot page that I am missing, but I didn't hear back. I hope he is doing ok.

These were the PC-122 pages he had on CBTricks. Converting them to PDF did tweak the backgrounds a bit because, unlike a web browser, the pdf version didn't duplicate the background image going down long pages and some defaulted to black (like the text) so I had to change a couple html color codes, but thats it.

edit: I see it also offset the text in some of the yellow boxes splitting it between pages, but I think the text is all there. I will add the html files and supporting graphics folders in a zip too because it looks like it did on cbtricks when opened that way.

 

[MKwrench]

I hope HandyAndy don't mind me sharing this. I messaged him here a few days ago about these files, also inquired about the yellow dot page that I am missing, but I didn't hear back. I hope he is doing ok.

These were the PC-122 pages he had on CBTricks. Converting them to PDF did tweak the backgrounds a bit because, unlike a web browser, the pdf version didn't duplicate the background image going down long pages and some defaulted to black (like the text) so I had to change a couple html color codes, but thats it.

edit: I see it also offset the text in some of the yellow boxes splitting it between pages, but I think the text is all there. I will add the html files and supporting graphics folders in a zip too because it looks like it did on cbtricks when opened that way.

Wow!
Thanks!