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Discussion in 'Amateur Radio Modifications' started by dxing440, Jan 19, 2017.
Andy had the correct transistor circled in yellow. From this view, the pin in question is the bottom left. It already has what looks like a "202" resistor soldered from this pin to ground right below the transistor. Parallel another 470 ohm resistor from that pin to ground. The screw in the corner is an easy place to pick a ground up. The audio will jump to life with the full 40 plus watts of PEP. Anything from 470 ohms to 1k works good here. If the value is too low you may start to hear "pumping action" from the AMC. That symptom would be heard as a sudden reduction in mic gain on the first loud sound the mic picks up. At 470 ohms and with too much mic gain, this can be noticed. The 1k resistor eliminates that but has less AMC range.
Nothing with the mic gain or pre-amp stage can get this radio to talk well before the aggressive AMC circuit is modified to provide a decent adjustment range. Otherwise you just get more background noise with no higher audio peaks. The stock mic is a little lacking in tone quality but the use of the Motorola microphone pre-amp makes the rig sound great. That pre-amp has been discussed here and has been built right into the stock mic with no battery needed. That pre-amp helps with the tone because it breaks the DC line to the mic and inserts an appropriate value coupling cap in series. It also has enough gain to compensate for the loss in the added cap.
-Realize folks that the SMD transistor pinout are not always "standard"...so some care had to be taken...to preserve the radio...
Wow, this radio suddenly has a lot of potential. Not too expensive either, might just pick one up to play with. Thanks for sharing the mod!
Yes thanks to Shockwave and Andy, *tips Fedora*, haha.
You're quite welcome.
"Facial Recognition Software" has got nothing on you.
Would love to give you a tour of the place but Wife won't hear of it - so I have to respect that (Mom issues)
But I will keep your post close to the heart - keep your self safe man.
That’s not me but I do have the G.F. mask, haha.
If you want one to tinker with get the anytone Apollo 2, it's identical other than the badging at a lesser cost.
Andy, you're like MacGyver! Sometimes I have to read your teachings over a few times because I get lost trying to process it. Time and time again I see you schooling us bro. You could easily say to us as my uncle once said to me when I'd think I had it all figured out but didn't "remember I taught you everything you know, but not everything I know"
Naw man, I learned all this by helping you guys.
I had questions too!
So why not share in all the fun I had digging this up and putting it together in a way it's "digestible" (Readers Digest - anyone? LOL)
No, I can't take the credit man, this stuff is fun to learn about.
It's folks like you that bring this radio to the table and we can all just kinda' sit around that table and talk about it - each person sees it in a different way and everyone learns by doing - so I learned a lot.
I have you guys to thank for this.
Thanks to you Shockwave, I showed your post and my post to the techs at Stryker and they were nice enough to try the mod out on the sr94hpc themselves with success. Then I did the mod with excellent results. Good job man. Now this radio screams like it should. 45 plus watts just like you said.
You had better luck with any Tech at Stryker than I did. They were very resistant about providing the slightest bit of info on this radio. Not even a schematic. Insisting that I should not attempt any mod of their AMC. The conversation shut right down when I pointed out how the radio was falsely advertised as having a noise blanker when it only has a mislabeled ANL too. Needless to say without their help it only took removing the board 6 times to trace the signal path down to that one limiting transistor. The results are worth it.
Does anyone have a schematic for this radio, or are they unobtainum like the Anytone Smart CB/Albrecht AE-6110?
How does it look on an O'Scope after the Mod?