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DX 2547 Red Wire Mod?

Robb,

You are correct, I do not remove the AM modulator limiter, as it's not necessary.

It's really hard to cause damage with my mod. The idea is to keep everything in operating specs, so nothing sees over-voltage and such. All limiters are intact and adjustable so maximum negative peak compression is achieved without flat-topping, and allows adjustment (within reason) based on the deadkey. "Volting" the final is not necessary, nor is it needed, and generally does not work well in base CB's.

~Cheers~
 
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sp5it said:
AM limiter must be removed. Properly done npc-rc and you are unable to overdrive or produce flattops because of that circuit.
But: it needs to be done right way, not by butcher from interstate container.
Mike
Click to expand...



“ . . butcher from interstate container”, (that’s one for the ages).

You got my interest on the mod, I’ve tried reading around, I’ll see if I can’t find a video or something with convincing before/after audio.

And I get other observations about problems as scoped.
 
Last edited:
ExitThirteen said:
Robb,

You are correct, I do not remove the AM modulator limiter, as it's not necessary.

It's really hard to cause damage with my mod. The idea is to keep everything in operating specs, so nothing sees over-voltage and such. All limiters are intact and adjustable so maximum negative peak compression is achieved without flat-topping, and allows adjustment (within reason) based on the deadkey. "Volting" the final is not necessary, nor is it needed, and generally does not work well in base CB's.

~Cheers~
Click to expand...

Also on the 959 chassis?
 
It’s for some, some it’s not. I like it, works well when done “right” and the operator follows your directions.

We really deserve a “story time with Uncle Nomad”, the wording & writing here made me feel like I was watching a movie voiceover like in Stand By Me. Hahaha.

nomadradio said:
The ghost of Reverend Billy.

As in Billy Dean Ward. He originated this trick, called it "NPC/RC", as in Negative Peak Compression/Reduced Carrier.

Like light beer. Some folks swear by it, others swear at it.

The snippet of black heat shrink tubing contains a diode and a resistor, usually 100 ohms in series. It alters the negative feedback in the radio's AM modulator circuit to over-emphasize positive peaks. Also tends to nearly remove the negative side of your audio waveform, below the carrier level. Never did see a point to losing half your audio waveform. You need all of it.

The "Red Wire On Bottom", or RWOB is used to jumper around the radio's modulator transistor, feeding a steady 13.8 Volts DC to power the finals. Now the AM modulator is only modulating the driver transistor. In all fairness, the modulator transistor does breathe easier in this setup. Finals may work harder, though.

Mostly a wattmeter worshipper's trick. I found that the carrier setting becomes critical with this mod installed. Too low and it sounds terrible. Too high and you lose your modulation level. Makes it sound as if you turned down the mike gain. Set the carrier at the 'sweet spot' and it sounds okay. Not my idea of a way to set up a radio with a carrier-power knob on it.

Billy championed his pet idea as if sliced bread was never really a big deal. Full disclosure: he was an ordained Church of God minister.

Yeah. But he died a few years ago, slumped over his bench if you can believe the rumors.

But that's the short version of NPC. Anyone who is curious is fully entitled to investigate it, try it on your radio and make up your own mind. But once you see what the radio's AM transmit is doing on a 'scope you will probably uhnook it and put the radio back like it was.

That's what I did. Decades ago.

73
Click to expand...
 
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TheRealPorkchop said:
I like Nomad. Plus neither of those guys are here or know anything about the stuff we’re interested in.
Click to expand...


Among Hollywood’s highest paid voice actors, so I’ll disagree. It’s all in fun.

So you want the Louisville Larynx to do his own narration, okay. Any CB guy you have to figure has a developed ear. Maybe he works at the Cronkite 126-wpm cadence vs the normal American 165-wpm. Might color ones idea of fast attack, though.

We all want these radio prayers of ours to put on a suit & tie, don’t we?


I’ve tried to find excuses for several years to get to his shop, but parking a ‘53 there ain’t gonna work.

.
 
been seeing more and more discussion about this mod and all of its variations, and thought this would be as good a place as any to throw my 2 cents into the ring.

I have tried and tested pretty much every version of this mod, and over the years have come to the conclusion that it is a very cool mod, but is not for everyone or every situation.

if you are someone who changes their deadkey level in order to use different amps, then this mod is not for you.

this mod is specifically for people who want to lower the deadkey of their radio in order to properly drive an amplifier, but would like to have their modulation swing up as high as the radio will allow, while still maintaining a decent waveform on the scope.

If you do not use a scope to set this mod up, then it is no different from the standard swing mods we have all seen.

first, do not do the red wire on the bottom thing.
there is no need to volt the final when doing this mod, and IMO it works much better when you don't.

also, do not clip any limiters. if you do, you won't be able to keep a clean waveform.

step 1: replace AM modulator transistor with TIP 36. align radio.

step 2: for a single final radio, set the deadkey to 2 watts.

step 3: using a scope, set the modulation for 100%.

step 4: solder a diode (1n4148 works just as well as the 1n400x) to a 1K trimmer resistor.

step 5: solder the diode trimmer combo in parallel with the correct capacitor.

step 6: key the mic and apply a 1K tone.

step 7: adjust trimmer for nice round negative peaks.

step 8: remove diode trimmer combo, and measure resistance on trimmer.

step 9: replace trimmer with fixed value quarter watt resistor, and re-solder into radio.

there may be a bit of playing with the AMC VR in order to get it right, but that is basically it.

i have never had a radio come back to have this mod removed when done this way.
LC
 
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loosecannon said:
been seeing more and more discussion about this mod and all of its variations, and thought this would be as good a place as any to throw my 2 cents into the ring.

I have tried and tested pretty much every version of this mod, and over the years have come to the conclusion that it is a very cool mod, but is not for everyone or every situation.

if you are someone who changes their deadkey level in order to use different amps, then this mod is not for you.

this mod is specifically for people who want to lower the deadkey of their radio in order to properly drive an amplifier, but would like to have their modulation swing up as high as the radio will allow, while still maintaining a decent waveform on the scope.

If you do not use a scope to set this mod up, then it is no different from the standard swing mods we have all seen.

first, do not do the red wire on the bottom thing.
there is no need to volt the final when doing this mod, and IMO it works much better when you don't.

also, do not clip any limiters. if you do, you won't be able to keep a clean waveform.

step 1: replace AM modulator transistor with TIP 36. align radio.

step 2: for a single final radio, set the deadkey to 2 watts.

step 3: using a scope, set the modulation for 100%.

step 4: solder a diode (1n4148 works just as well as the 1n400x) to a 1K trimmer resistor.

step 5: solder the diode trimmer combo in parallel with the correct capacitor.

step 6: key the mic and apply a 1K tone.

step 7: adjust trimmer for nice round negative peaks.

step 8: remove diode trimmer combo, and measure resistance on trimmer.

step 9: replace trimmer with fixed value quarter watt resistor, and re-solder into radio.

there may be a bit of playing with the AMC VR in order to get it right, but that is basically it.

i have never had a radio come back to have this mod removed when done this way.
LC
Click to expand...


I saw some of your now ancient posts as I read around on this, so appreciate the detailed answer.
 
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tecnicoloco said:
Hi ExitThirteen can you share or explain how your mod is done on the MB8719 ?

TIA
Tecnicoloco
Click to expand...


I don't feel like im stepping on exit13's toes by putting the mod out there since it's already in other threads on the forum.

so, first make sure your particular MB8719 has a variable AMC. (some have a fixed resistor and they need to be replaced with a trimmer)

next replace the AM regulator with a TIP41.

then remove R228 and replace it with a 1K to 1.2K resistor.

solder a 1uF non polarized cap from pin 9 of the audio chip to the junction of R194/D63/R228.

set deadkey for 1 or 2 watts.
use scope to adjust AMC.

i typically see positive peaks of about 130-150% with this mod.
the higher you set the deadkey the less "swing" you will have, just like the other NPC mods.

i just have to say thank you again to Exit13 for coming up with this mod, as it is the best ive ever seen for modulation mods for this chassis, and is the only mod i ever do to them anymore.
LC
 
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