Then that is related to a R149, R151 / R152 stuff...
But I also realize, by looking at what I manually saved off of CB Tricks - the very page I found the above, isn't on their "Classic" site...So what you're going to see here is a recreation of the pages, via the "Cut - Paste" method the ones you don't see at the CB Tricks site - as well as many others that have been brought up before...
This thread may become long in the "tooth" due to the number of graphics and work that is a part of the "HandyAndy" side of CB Tricks...
This will be Edited due to the time frame this was made was when parts these radios used, were more plentiful - it's been nearly 20 years since these radios have been closed out...so now I'm more focused on the preservation - and if done with, and in consideration for others, several mods that can be applied that won't make the radio suffer greatly...
The Board Reference and Identification Page...
To help the user identify the correct board and then apply the correct mods...
Why would this matter? Well, review the Schematics of two popular radios that looked a lot alike both outside and inside...performance between the two was different - but not by "big changes" more like subtle small part relocations that had a big impact on how your radio worked.
Some examples above are shown below...
TRC-453 TX Strip (as shown above)
Locate C180 on Schematic then on Main PCB
C187 - even see it? It's mounted on the bottom on some
on many - it wasn't.
TRC-465...
In this comparison, refer above too...
C180 - now PAST the Driver
R195 - 2.2ohm in 453, now removed - Left L32 in
C211 and C145 divider/parse down RF power from the Driver
before it arrives to the Final.
R173 - was 8.2 ohm, now 15 ohm - Q38 Pre-Driver
R172
12 ohm! (TRC-453 150 ohm)
I'm advising you the 2166's are not OEM anymore...
PC-122 Mobile/Pro-810e BASE
Using the list of parts above, compare...
See C134? Look on your Board - part value changes!
Again, 2SC2166 Driver is hard to obtain OEM anymore...
What I also needed to show is the SAME BOARD (PC-122 and TRC-465) are electrically similar, but they use different part values to obtain different levels of performance...
What I'm showing you here is -
Options.
Some like RF compression effects; the AM Modulation and SSB Envelope works in specific ways.
While others would rather have Swing and Loud Modulation without the "pinch effect"
- - both can be done to some degree by changing the VR pots to obtain a level of AMC/ALC works and also the AM Power and how it then lowers Carrier reference so it changes how AM Power works.
In a typical Galaxy radio - they introduced a form of regulation for Variable power in both AM and SSB modes;
In this smaller radio board - you have to make changes to the Limiter action - either by desensitizing the input to the Modulation Control Circuit - which looks to Both AMC and ALC taps;
When in SSB mode, Q29 is essentially cut off,
SSB receives full Supply rail power with no audio
- done thru SSB switch Q38
Or by affecting the way the Modulation Control stage works, by changing it's values...
ALC taps RF at the output when in SSB mode - it's pinched off in AM mode by D41 pushing power into the "power leg" Q34 - and works accordingly to the amount of RF power than can turn on Q34 and pull power from the PNP Modulation Amp - Q28 (2SA733) by using the adjustable level of power set by R178 (22K) and VR6 10K acting as a voltage Divider to set thresholds the ALC sends to the Modulation Amp.
Look back up at the R151 Discussion graphic, locate R149 a 1M resistor - this works with R148 to form a tight divider circuit that forces the PNP transistor Q28 to follow the output lines of Q29 or Q34 as they fluctuate with their tap signal levels. R146 and R147 form a Split divider (equal) for the output of Q28 reflecting the ALC or AMC sections - into the Limiter Q27. This puts the Limiter Q27 (NPN 2SC945) into a Linear state - like Class A which then allows Mic audio to pass thru itself into ground with the Base of Q27 being the "Valve" the Mic audio passes thru - less audio - less drive - less Mic Audio is siphoned off - it's allowed to pass into the Mic amp itself - until spikes or thresholds set by VR6 and VR5 engage Q28 to provide more drive current into Q27 - C113 along with R148 and R149 develop the Attack and Delay (Decay) of the drive signal Q28 drives Q27 with - forces Q27 to drive more Mic Audio into Ground - and due to the use of C111 R144 and R161 - allows the low-level Mic Audio Signal to flow into ground somewhat linearly.
- I use Somewhat as tongue in cheek,
- for Mic Audio itself - as low signal level as it is arriving to the Mic amp stage - the Limiter is driven non-linearly by the efforts of Q28 and the bias network it uses, not from the "amplification of Q27" provides, The Limiter itself (Q27) is only acting as a linearly-driven switch against the Mic Audio - which is weak signal level in itself so audio from it tends to suffer from the non-linear drive Q28 drives Q27's Base with.
- To solve that? Well, mostly by changing the way Q28 works in the first place, and also inclusive by working with the sensitivity the ALC and AMC - their Aggressiveness - and how works on Q28.
- So R151, R152 along with R148 (1Meg) and C113 can be altered to different lower values to allow the operator some range to control the activity and how hard the limiter works - which in turn can affect how well the operator sounds to others.
- To enjoy the radio more, please don't try to remove the limiter if it can be avoided - for there are reasons in the RX side that is why it is in there.
- Review your schematic carefully and you'll see where the Mic and Receive Audio can Mix together in the common tie point of C170 at the Audio Amp. For the Mic audio strip remains powered during RX and TX - so there are conditions that can inject noises the Mic amp can amplify if the Limiter is removed.
For some simple results - trying to change the way Q28 works is done thru changing R148 and R149 aspects - focus more on R149 1 Meg - which is a large value resistor that forces Q28 to operate harshly as a switch than a linear analog - audio - amplifier tracking signal - the lower R149 is, the more balanced the audio level to drive output is improved.
C113 can also be changed to alter the attack and decay of the signal pulses that show up during keyclicks and noises the mic amp will attempt to push into the Transmit audio either by SSB modes or thru the AM Regulator. The lag time the Limiter takes to recover is thru the R148/R149 and C113 ranges of values used.
