Realistic TRC-427 Audio Mod 'GoldFinger'

[Handy Andy]

In a similar vein...

The feedback resistor I was talking about - the one that the Grant's and Cobra use for controlling AMC (Why people pull R131) R166 (3.3K) and R165 (1.5K) - is similar to the PC-122's R151 "Divider" resistor that sends the envelope power to the AMC circuit but also provides a level of compression for the audio envelope - forcing am audio "image" symmetry into the envelope - that develops stronger peak compression levels at the PEAK TONAL RESPONSE range the envelope is tuned for. R166 is a gain value that is applied to R195 and D54 - helps the other half of the balance symmetry of D63 and C173 Recovery times (aside from the inherited delays brought on by VR10 R196)

What that means is; many an enthusiast changes the "gain cell" electrolytic (C177 is above graphic C173 for Grant / 148's) to a higher value like 100uF to 220uF - all you get is bass response - that's the point of the envelopes' peak tonal response curve for envelope - that is why I call it a "gain cell" for it holds/sustains envelope power for the lower bassy tones and provides some of that needle movement "swing" that shows forward audio power.

It also is what causes the carrier "Fall" in the NPC mods, for the gain cell can't recoup a charge until a set time delay, the larger that cap, the greater the delay in recovery time. Again in the "THE PAST" graphic, that uses the 220 ohm 1W resistor to affect the recovery time - which if you guys play with NPC mods, you may need to adjust your carrier swing and recovery times by using a similar method and values - higher for long delays and 220 ohm for "standard" recovery rate for envelope audio power to carrier swing level. Again, uses the feedback resistor values to affect gain (punch) of audio in the envelope as well as level on AMC detect for those that wish to play along at home and use the limiter - for safety's sake...

 

[LeapFrog]

I've played around with & without the 220 Ohm from emitter to collector, I should try 390 Ohm just to see if I observe any changes in the way it operates. The regulator runs cooler with the resistor.

It seems (I'm bad at recording data at home) I had more average power with the resistor, but higher modulation % without it (increased heat also). Having all of the DC bias "carrier voltage" coming out of the emitter of the regulator, it definitely runs warmer.

 

[Handy Andy]

Glad to see you're trying different values, much of the dynamics of Audio "punch" rely on extremely wide range of impedance "Drive" (Dynamic Range) across TR41...that "too much" (No resistor) can hurt you if you don't provide a means to recover equilibrium and get the carrier back to "center" as soon as possible (Blown part for one).

Although the 220 ohm (R193) seems to soften it (Audio Punch), not by much, makes the signal cleaner - not necessarily "clearer" but does handle the linearity of the load swing the audio imposes on the 1419 and any that use SA473/SA1015 and 2SA1012 / BA745 styles (runs parallel as a load resistor) - makes the part run cooler and provides (some) longer life - as well has improve the recovery times the Grants' / 148's need for their C173 to act normally again.

R193 - it simply sends part of the DC battery supply across the 1419 (Mains) and this affects R166/R165 too - it's a poor mans way of keeping Negative Swing more positive. (AMC Recovery) And the Envelope? It uses the C173/D65/R194/R228 and it's gain for impression of Audio onto the DC Bias - it's why VR10 and R196 are they way they are - allows C173 to push carrier DC bias upwards once audio depletes it - restoring symmetry, some "lag" is needed to obtain some ability to prevent excessive "compression" else all you'd need is the R195 and R195 for symmetry - it would then result more in "Monotone-ish" and more FM sounding (pinch) - so the C173 provides the "pool of reserves" for the "Punch" the audio will have.

 

[711]

Cool, I didn't know that a copy was floating around of his early build.

Yeah I never got an opportunity to join the CB Tricks forum, so I don't know anything about the discussions that took place there.

The modulator more closely resembles what is found in the Grant XL/Cobra 148 GTL, looking at the PC-122XL schematic I couldn't find the familiar Darlington configuration, but it very well could be present.

"Nothing special" could be said about any circuit.
But I agree the modulator itself is rather simple.
With processing it works a treat.
The rest of what he does is to get more power output.

I'm not releasing his mod process, detailing the work on the RF section, I will just be covering the modulator itself.

For anybody wondering.. the "Darlington modulator" or "series pass modulator" install is not about increasing power of the radio, it's about audio and modulation percentage.

Cool bro, good luck with your solder slinging. I'm out. Whats up Andy

 

[LeapFrog]

Enjoy your experimentation also..
I don't "sling solder" until I've had my morning coffee, cheers!
&
Kind Regards

PS this thread has served its purpose.
PM's work great for shout-outs too.

Edit: the PC-122XL modulator is not setup like the 148, compare the schematics.
Look where the audio comes from for one thing.
But I get it, an AM regulator is an AM regulator.

 

[Handy Andy]

Busy day...

Awaiting for Spring to come, welcome to Winter...SIGH...

 

[TheRealPorkchop]

Stop talking about it and maybe it’ll go away. I hate the cold. Thankfully no snow yet. Just cold.

 

[LeapFrog]

No winter field day for me.

I'm loving the sunshine state.

 

[snow bird]

Stop talking about it and maybe it’ll go away. I hate the cold. Thankfully no snow yet. Just cold.

I just re poted 48 tomato plants >Wating For Spring< long Winter ,

 

[Handy Andy]

No winter field day for me.

I'm loving the sunshine state.

Now, did you take that as a Black and White photo of you sitting on the beach?
Tint it blue...
then re-post it to make us think (pity you?) that you're out there in the tundra...

You're mean!
LOL

 

[Shadetree Mechanic]

I was googling AM modulators and found this again. Now reading this for the second time, I am able to understand a little better. Going to go back and read one more time. Bump.

 

[newoldguy]

alot of great info here thanks to all who share

 

[Redbeard U812]

I've got a 427 on the shelf. If I remember, it's a pretty loud radio. Ran it for kicks and giggles but that din plug was terrible. Mic cord kept coming out. Got it in a batch of radios about ten years ago. AM only.

 

[Shadetree Mechanic]

Bump

 

[freecell]

"People can’t hear sounds < 20 Hz and > 10,000 Hz very well. If you turn up the volume on your device to compensate, you could expose yourself to harmful sound levels and your speakers to harmful currents. To be safe, note the volume level that allows you to listen to a 1,000 Hz tone without discomfort and do not stray too far above this level, even if you can’t hear much – especially in the high range, where your hearing is the most fragile."

set the audio level for 30% (the same output level used with a signal generator to determine receiver sensitivity) and scan the range. listen for the peak in output between 1000 and 1100 hz.. the output level is practically non-existent below 50 hz. and above 10 khz..

https://www.szynalski.com/tone-generator/

you can click on any adjustable control and toggle it with the keyboard directional keys.
to select an exact frequency you can click to edit the generator operating frequency.

afterwards, ask yourself the obvious question.