Tuesday, April 7, 2009

Uniden PC 66 and PC 68 Audio and Power Mods

Here is a simple $5 way to crank your Uniden PC 66 or PC 68 radio to be a loud talker.

Parts you need.
35volt 220uf Electrolytic Capacitor
10 Ohm, 1watt resistor

1st we'll do the audio.
There is no internal VR# adjustment pot to turn up on this radio, just on the front.
Doing a few small mods opens it up about 40% more audio. You may not need any power mic after this mod.

On the PC 66 look right below the mic connector.
On the PC 68 its on the front right side, near the edge fine these 4 parts.
R76 Remove and add Jumper wire across this.
R78 Remove (Added resistance on audio line to ground)
Q14 Remove (Mod Limiter)
C97 Remove (Filtered Audio to Ground)

This basically opens up the restrictions on the audio pre-amp circuit.
If you plan to use a good power mc, you might need to leave C97 in to reduce RF squeal or hum.
Some people prefer to leave the mod limiters in, to reduce splatter, but for a LOUD radio, I a remove it on this model.

Next is the power output.
This is a touchy subject for some people, but I prefer to use "swing kits" in my radios.
I like to have my radio deadkey low, and swing high when I talk.
This add a lot more audio and "punch" to your voice.
What it basically does is lowers your output when your not talking, and raises it when you do talk. This reduces the power load on the radio, due to poor design, and "reserves" some power for your audio.

To add the swing kit, find JV17 in the back of the radio, in front of the Final.
Remove this jumper wire.

Now install your 35volt, 220uf Capacitor in this spot. Use the NEGATIVE side in the hole towards the BACK of the radio. Insulate the wire with tape or heat shirnk tubing to prevent it from shorting the metal nearby.

Now flip the radio upside down.
Find where you remove the jumper wire, and install the 1W, 10 Ohm resistor.

Now that you have installed everything, tune the radio. On most of these radios, you dont need to adjust the L10 coil, but some radios are off a little bit from the factory.
Spread the coils on L8 apart slightly.

You can also replace the c2028 Final transistor with a high power 2sc1969. This will be a great mod, if you can happen to find them, as they have been discontinued and are getting harder to find new.

That's it!
Thats the secret to tuning up a Uniden PC 66 or PC68.
Save yourself $20-50 at a radio repair shop, if you want to do this work yourself.

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