Realistic TRC-458 Clarifier mod info.

[dxing.bruce]

Hey: Guys.

I want to open the clarifier on my Realistic TRC-458 UPD858C chassis.

I have the info on how to do the modification but once it's open I have read
you get 3k down & 1K up in swing. I there a way to balance this out so you get
1.5k to 2k each way ?

I find it kinda useless if it swings too much one way.

My understanding on the stock " closed " clarifier on most cb radios gives
approx 1.5k swing for the receive both ways so why does opening the clarifier
change that to 3k down & 1k up ?

Any info would be greatly appreciated.

Bruce.

 

[Handy Andy]

It's how the varactor works - the 858 chassis - at least to "center" the onboard stock varactor - needs a padding resistor - so the linear region of the varactor makes the slide even up or down - but padding comes at the price of slide width - making more slide requires the mod be done, but to use a less drastic mod, would be to pad the clarifiers LOWER (to ground side) to keep linearity - but whom wants to play with 680, 560 or 750 or 820 ohm resistors just to improve some slide, keep the knob centered and then on top of that - have some thermal stability?

I used to but it becomes unmanageable when too many people want the same result but use different chassis - not everyone used an 858 - so I quit doing the reduction but not zero method to keep my sanity.

 

[dxing.bruce]

It's how the varactor works - the 858 chassis - at least to "center" the onboard stock varactor - needs a padding resistor - so the linear region of the varactor makes the slide even up or down - but padding comes at the price of slide width - making more slide requires the mod be done, but to use a less drastic mod, would be to pad the clarifiers LOWER (to ground side) to keep linearity - but whom wants to play with 680, 560 or 750 or 820 ohm resistors just to improve some slide, keep the knob centered and then on top of that - have some thermal stability?

I used to but it becomes unmanageable when too many people want the same result but use different chassis - not everyone used an 858 - so I quit doing the reduction but not zero method to keep my sanity.

Ok, but that does not answer my question in that I'm not trying to get more slide, when the clarifier is closed I believe it slides 1.5k each way on receive. All I'm trying to do is with the clarifier opened is to also get 1.5k slide per side rather than 3k down & 1k up. The only reason I even want to open the clarifier is with different temperatures all radios tx frequencies drift slightly & with the clarifier opened I would at least know if I'm hearing people clearly with the clarifier then I should be transmitting at the same spot as compared to say transmitting 200 to 500 hz low but hearing stations clear at clarifier center. I thought maybe adding more resistance to one side of the clarifier control than maybe that would center it once it's open so it would slide the same amaount up & down.

 

[nomadradio]

That one's pretty straightforward. One diode D30 gets unhooked at one end, or just removed altogether. This disables the "fixed" transmit side.

The resistor that feeds the front-panel control gets removed and moved onto the solder side of the pcb, where it will reach to a source of continuous 8 Volts DC that stays on for receive and transmit both.

Here's a pic of the diode D30 that gets removed, or showing where it was before removal.

Imageshack has somehow lost the 'before' picture showing where on the top side to remove R119. It's a 100-ohm resistor. Brown-black-brown. But at least they didn't lose the 'after' pic showing where R119 will go on the solder side of the board.

But these are the required two steps for most any 40-channel CB radio. First unhook the transmit-only circuit. Then move the power source for the front-panel knob away from the receive-only voltage source, to a continuous voltage source.

73

 

[nomadradio]

Hmmm. Note to self. Read for comprehension.

You asked about making the frequency coverage of that knob more balanced left-to-right.

Two obstacles here. The PLL has three crystals attached to the clarifier circuit. Naturally only one of them is active at any one time. One for LSB, one for USB, same for transmit and receive.

One for AM receive only. When you transmit AM, that crystal shuts down, and the USB crystal kicks in until you unkey.

This is a sort of wild card in the deck. Each crystal will respond a bit differently to the clarifier.

A look at the clarifier circuit in later Uniden SSB CB circuits that used the MB8719 PLL reveals an effort to do this. Adding a resistor from the clockwise lug to the wiper lug will serve to skew the coverage one way. A resistor from the wiper to the CCW lug will skew it the other way.

A 1k resistor in series with a 10k trimpot is where I would start. The fixed 1k resistor keeps the resistance high enough to avoid overloading the front-panel control. The tuning rate, in frequency per degree of turn is highest to the left of center, most of the time. Putting the trimpot between the clockwise lug and the wiper lug is where I would start.

Naturally, this will change the center-frequency setting of the three trimmer caps with the knob at 12 o'clock when it's adjusted.

73

 

[hpssb]

Here's how our tech told us to do it. Works well with shift the same amount in both directions and the 12 o clock position is at the exact center frequency.

1) The hot wire that originally fed rx only voltage is removed and replaced with a feed from constant 8/9v via a 100 ohm resistor.

2) The cold terminal goes to a resistor on the pcb and the other side of the resistor is ground, remove this resistor and replace with a wire link.

3) Remove the tx voltage source component, usually a trimpot but sometimes a diode.

4) Check it now works as unlocked and transmits and receives on the same frequency.

5) Adjust the frequency trimcaps or tuning inductors for maximum range on each mode lsb and usb. Don't try and center it yet with these adjustments, just go for maximum range at the high end.

6) Put the clarifier at center 12 o clock position and add a resistor from the center terminal to either hot or cold to bring it to as close to exactly on frequency on lsb you can get with the resistors you have on hand.

Connect it to hot to raise the frequency and cold to lower it.

A higher value resistor gives less shift, a lower value gives more. Start with 4.7k and go higher or lower to suit. One of those resistor wheel things is a useful gadget for this step.

Fit the resistor permanently, then do a slight adjust the frequency trimcap / tuning inductor to precisely center the lsb frequency.

7) Leave the clarifier at 12 o clock, put radio on usb, and adjust the usb frequency trimcap / tuning inductor to center the usb frequency.

Done! With our cobra 139 base and gladiator mobile which are both 858 chassis, it gives about 3k to 4k up and down either side of center and 12 o clock exactly on center.

Loz!

<edit, add half line missed from copy and paste operation>

 

[Handy Andy]

I have the info on how to do the modification but once it's open I have read
you get 3k down & 1K up in swing. I there a way to balance this out so you get
1.5k to 2k each way ?

A higher value resistor gives less shift, a lower value gives more. Start with 4.7k and go higher or lower to suit. One of those resistor wheel things is a useful gadget for this step.

Between both I said...

but to use a less drastic mod, would be to pad the clarifiers LOWER (to ground side) to keep linearity - but whom wants to play with 680, 560 or 750 or 820 ohm resistors just to improve some slide, keep the knob centered and then on top of that - have some thermal stability?

So if the question didn't get answered -

What was your question?

How to do the clarifier mod?

or

How to "Center" the clarifier once the mods' been done?

 

[dxing.bruce]

Between both I said...


So if the question didn't get answered -

What was your question?

How to do the clarifier mod?

or
How to "Center" the clarifier once the mods' been done?

To center the clarifier once the " open clarifier mod is done " So I will have even slide to the + and -

All the info I have read says that once the mod is done you get 3k down & 1k up. I just want the clarifier to track even both ways even if it's the same amount of slide as when the clarifier was closed.

I was just looking in the service manual for the Realistic TRC-458 & they say the clarifier tracks 1.25k up & down. I would be perfectly happy with that with the clarifier open.

So is there a way to have the clarifier " open " & still have 1.25k slide for the + and - on the clarifier. ??

Thanks in advance.

Bruce.

 

[Dmans]

pad the clarifiers LOWER (to ground side)
to keep linearity
play with 680, 560 or 750 or 820 ohm resistors
keep the knob centered and then on top of that - have some thermal stability?

(Above condensed-yet again-from @Handy Andy post #2 of this thread)

Fingers Crossed here.

73
David

 

[Handy Andy]

Well, to help with an example is say the 148GTL...

When you go to a constant source for the Clarifier - I only worry about "center slot" - being that most people won't notice, or care - about the slide being greater - they just want to talk to their friends.

The easier you make the conversion - the less hassle the issue of slide becomes - for most won't use the extremes for the issues of stability are MAGNIFIED on both sides of the center slot - on any potentiometer.

The main idea here is as you work thru your conversion - if you keep the values, all the same - the only thing you may need to do later is tweak the coil for the mode to help bring the clarifier back to center slot - if any adjustment is needed.

Here's a thread I found from another user that might help shed some light on the issues I speak of, one being that most of the time - people change the external control "range" by changing or removing parts which gets you into trouble with case and chassis and parts getting clipped out or removed and the radio is never quite right until all the mods are removed - stock values brought in and soldered - then the PROPER rework needed by the customer simply wanting an "unlocked clarifier" but not all the slide or hassles with drift.

How do you solve for that? Simple - just remove RX and TX voltage - and just source the 8 V the PLL uses and send it to the Clarifier (Voice Lock)

Read this to help you

Cobra 148 GTL clarifier unlock.

I have a old beat 148 GTL that someone many moons ago unlocked the clarifier. I can align AM and LSB but USB bottoms out. Will changing the value of R236 8200 ohm give me more adjustment? Probably one of Andys little graphics would help From what I see this is the only resistor that goes to...

www.worldwidedx.com

Another...

Cobra 148 GTL mod

I am getting back into the CB world again. Back in the 70's I did alot of playing around with a GE AM/SSB unit with a 50w Polamar amp. The GE radio is gone but I still have the amp. I now have a Cobra 148 GTL sside 5 pin mike. I have made the modification to the receiver for increase rf...

www.worldwidedx.com

These deal with Cobras, but when you work with the TRC-458 - you'll see much of the discussion can apply to nearly any radio with a clarifier tied to a coil/crystal/cap tune design - simply by the source is varied by a pot set up a specific way to treat the varactor with SMALL changes in voltage.

It's how the voltage is applied in the circuit that the varactor is in, develops the IMPEDANCE load the varactor uses to tune its capacitive range with - you'll see various principles of swamping resistance and capacitance used on that clarifiers' line to the varactor - and how much of one affect how little or large that variance becomes against the tuning range.

Thats why your question is really two-fold - one being - doing the clarifier unlock procedure correctly and then tweaking the clarifier circuit to tune - and keep the clarifier's' "center-slot" so you can tune equally in both directions.

Don't worry, you're doing fine, I don't think we want to start throwing curveballs at you just yet until you're more comfortable with understanding how this game of clarifier unlocking works.

 

[dxing.bruce]

Well, to help with an example is say the 148GTL...

When you go to a constant source for the Clarifier - I only worry about "center slot" - being that most people won't notice, or care - about the slide being greater - they just want to talk to their friends.

The easier you make the conversion - the less hassle the issue of slide becomes - for most won't use the extremes for the issues of stability are MAGNIFIED on both sides of the center slot - on any potentiometer.

The main idea here is as you work thru your conversion - if you keep the values, all the same - the only thing you may need to do later is tweak the coil for the mode to help bring the clarifier back to center slot - if any adjustment is needed.

Here's a thread I found from another user that might help shed some light on the issues I speak of, one being that most of the time - people change the external control "range" by changing or removing parts which gets you into trouble with case and chassis and parts getting clipped out or removed and the radio is never quite right until all the mods are removed - stock values brought in and soldered - then the PROPER rework needed by the customer simply wanting an "unlocked clarifier" but not all the slide or hassles with drift.

How do you solve for that? Simple - just remove RX and TX voltage - and just source the 8 V the PLL uses and send it to the Clarifier (Voice Lock)

Read this to help you

Cobra 148 GTL clarifier unlock.

I have a old beat 148 GTL that someone many moons ago unlocked the clarifier. I can align AM and LSB but USB bottoms out. Will changing the value of R236 8200 ohm give me more adjustment? Probably one of Andys little graphics would help From what I see this is the only resistor that goes to...

www.worldwidedx.com

Another...

Cobra 148 GTL mod

I am getting back into the CB world again. Back in the 70's I did alot of playing around with a GE AM/SSB unit with a 50w Polamar amp. The GE radio is gone but I still have the amp. I now have a Cobra 148 GTL sside 5 pin mike. I have made the modification to the receiver for increase rf...

www.worldwidedx.com

These deal with Cobras, but when you work with the TRC-458 - you'll see much of the discussion can apply to nearly any radio with a clarifier tied to a coil/crystal/cap tune design - simply by the source is varied by a pot set up a specific way to treat the varactor with SMALL changes in voltage.

It's how the voltage is applied in the circuit that the varactor is in, develops the IMPEDANCE load the varactor uses to tune its capacitive range with - you'll see various principles of swamping resistance and capacitance used on that clarifiers' line to the varactor - and how much of one affect how little or large that variance becomes against the tuning range.

Thats why your question is really two-fold - one being - doing the clarifier unlock procedure correctly and then tweaking the clarifier circuit to tune - and keep the clarifier's' "center-slot" so you can tune equally in both directions.

Don't worry, you're doing fine, I don't think we want to start throwing curveballs at you just yet until you're more comfortable with understanding how this game of clarifier unlocking works.

Thanks.

I was just thinking that there has to be an easy way to keep the swing exactly the same both ways. I know there is 8v on receive at the clarifier & not when transmitting so is there a way to just supply 8v to the clarifier pot all the time without clipping out parts ? I figured there has to be a way to do it. I know the standard mod is to remove D30 & R117 then take two of the wires from the clarifier pot & put one to 8v constant & one to ground. Can I just leave the diode & resister in place & simply take the wire that is only getting 8v on receive & attach it to 8v constant & get the results I'm looking for ?
I'm happy to have the same amount of swing to the - & + of 1.25k as the stock clarifier has I just want to be able to shift my tx & rx.

 

[Handy Andy]

Yes there is - several ways but the TX/RX switching in and out is the culprit for many epic fails of the clarifier conversions.

You really only need to locate the tie point for the 8V positive - you lift D30 (kill TX) and R119 - with the lift side being from the 8V RX side - that lifted leg is tied to 8V - the ground left alone will keep the slide the same.

Why keep R119 - for that center slot to work


The clarifier is regulated fixed input voltage - so R119 is the INPUT to the regulation.

So if you wish you keep center slot - lift R119 from the 8V RX side and solder a wire from your 8V Regulation or PLL's Pin 7 or 12 that 5V power supply.

Which is also a WARNING to others attempting more slide - the PLL does not tolerate voltages higher than its supply feed line - so if the power is 5V do not go above that voltage.

 

[dxing.bruce]

Yes there is - several ways but the TX/RX switching in and out is the culprit for many epic fails of the clarifier conversions.

You really only need to locate the tie point for the 8V positive - you lift D30 (kill TX) and R119 - with the lift side being from the 8V RX side - that lifted leg is tied to 8V - the ground left alone will keep the slide the same.

Why keep R119 - for that center slot to work
View attachment 59362

The clarifier is regulated fixed input voltage - so R119 is the INPUT to the regulation.

So if you wish you keep center slot - lift R119 from the 8V RX side and solder a wire from your 8V Regulation or PLL's Pin 7 or 12 that 5V power supply.

Which is also a WARNING to others attempting more slide - the PLL does not tolerate voltages higher than its supply feed line - so if the power is 5V do not go above that voltage.

Thanks Andy. I really appreciate your time.

 

[johnnytek]

pad the clarifiers LOWER (to ground side)
to keep linearity
play with 680, 560 or 750 or 820 ohm resistors
keep the knob centered and then on top of that - have some thermal stability?

(Above condensed-yet again-from @Handy Andy post #2 of this thread)

Fingers Crossed here.

73
David

build your own voltage regulator for THAT circuit using a lm 7808 with a 330 ohm resistor inseries to the ground TO the regulator.. adjust all corresponding viaractor variable capt to center 12 oclock. if need be, use a 10-15 choke in series with the cathode to further your center postition.