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Uniden 66XL help and tune tips

CB590

W9WDX Member
Jun 29, 2016
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Trenton Nj
www.590dx.com
8AA9365E-382E-46D9-91D6-4027C9FC444D.jpeg

Got this coming in. Was cheap enough and appears minty and supposedly only has talkback and tune. Does 4w and swings to 20w on guys Dosey.

Would turning L10 down lower my dk?? Or is there something else I should look to adjust?? I may decide to run an amp with it hence the questions.

What other things should I look for when I pop the top as far as cut things??

Happy New Years and thanks folks.
 
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How do I disable or remove the talkback someone installed.

Here's the pics. L13 slug missing. Mic jack has resistor going to top of L7 can on right.

200AC24A-30DB-4FBD-81F8-186C2EEAF734.jpeg

And corner where speaker plugs in

2C8975AF-1724-42DC-BA0F-1C7814E8FA46.jpeg
 
PC66 Overmod mod.jpg

PC66 Jumper JP6.jpg

Now, back to the original post about dead key adjustment, with this installed, it has a "swing kit" or "supermod kit", which lowers the dead key and the capacitor causes it to swing high on positive peaks of the audio. This replaces JP6. Depending on the resistor value under the capacitor, will determine the dead key. They usually cut off the negative peaks, having Zero carrier between spoken cyllables. Very hard to adjust correct modulation without an oscilloscope to watch the pattern.
If you put a jumper wire on the back side of the board, shorting across this resistor/cap mod temporarily, repeak the radio, then take the jumper off, thereby re-enabling the mod, the carrier should lower with the mod. Could also make it switchable.
 
Last edited:
the other guys have you handled on the talkback thing.

on that little cap on the bottom of the board, can you tell us which two components are being connected by it?

the solder to the case of the radio is just for the bypass caps that connect PC board ground to chassis ground.
CB radios used to all be made with what is called a floating ground, so that you could put them in positive ground vehicles.
that's why the chassis ground is not just wired right to the PC board ground, but is done through capacitors.


EDIT: NZ8N's method will work also.

as for lowering your deadkey, don't de-tune the can, as that just creates an impedance mismatch in the final section of your radio, and will lower swing as well as deadkey.

the way to do it is to add diodes in series with D10, the anti spiking diode located near VR3. i believe it's a 1N4003.
each diode you add in series will drop the voltage going to the collector of the driver and final by .6 volts, and therefore, will lower the deadkey.
keep adding them till you get to the deadkey you want.
the great thing about doing it this way is that all the audio will still be passed 1:1 by the diode since it's already biased ON when you key up.
try it, you'll like it.
LC
 
View attachment 32965

View attachment 32966

Now, back to the original post about dead key adjustment, with this installed, it has a "swing kit" which lowers the dead key and the capacitor causes it to swing high on positive peaks of the audio. This replaces JP6. Depending on the resistor value under the capacitor, will determine the dead key. They usually cut off the negative peaks, having Zero carrier between spoken cyllables. Very hard to adjust correct modulation without an oscilloscope to watch the pattern..

Could they have just cut JP6 all together and attached the cap legs to that?? It kinda looks like no resistor under it.

I was planning on running with my Palomar Elite 400 which can handle the 20w or so swing. And at the moment with this 66xl my meter is showing a hair under 100w dk. When I talk the power actually goes downward towards 60w and SWR climbs.

I did notice the L13 slug is missing also. Which is another tuning point for power. :/
 
the other guys have you handled on the talkback thing.

on that little cap on the bottom of the board, can you tell us which two components are being connected by it?

the solder to the case of the radio is just for the bypass caps that connect PC board ground to chassis ground.
CB radios used to all be made with what is called a floating ground, so that you could put them in positive ground vehicles.
that's why the chassis ground is not just wired right to the PC board ground, but is done through capacitors.


EDIT: NZ8N's method will work also.

as for lowering your deadkey, don't de-tune the can, as that just creates an impedance mismatch in the final section of your radio, and will lower swing as well as deadkey.

the way to do it is to add diodes in series with D10, the anti spiking diode located near VR3. i believe it's a 1N4003.
each diode you add in series will drop the voltage going to the collector of the driver and final by .6 volts, and therefore, will lower the deadkey.
keep adding them till you get to the deadkey you want.
the great thing about doing it this way is that all the audio will still be passed 1:1 by the diode since it's already biased ON when you key up.
try it, you'll like it.
LC

Talkback is now undone. (y)

The dropping of dk may have to just wait or be left alone. I'm not a tech at all. I always send things out, which you know is $20 each way to ship.

I have a harbor freight 30w iron that needs a new tip and no tools for more than soldering a wire or clipping one off.

Lowering the dk was just a thought. Just wish classic radios were left alone and not with torn out slugs and dodadds added.
 

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