| Author |
Message |
    
1861
New member
Username: 1861
Post Number: 3
Registered: 2-2004
| | Posted on Saturday, October 02, 2004 - 4:15 pm: | 
|
I JUST BOUGHT THIS OLD RADIO FROM A NEIGHBOR WHO HAS BEEN OUT OF CB FOR 15 YEARS . CAN ANYONE TELL ME HOW TO SET THE DK AND MODULATION , ALSO SSB MOD .? |
Tech808
Moderator
Username: Tech808
Post Number: 3725
Registered: 8-2002
| | Posted on Saturday, October 02, 2004 - 6:55 pm: |
|
1861,
Look to the LEFT of the forum here and you will see:
Tools
Mic. Wiring
Frequency Chart
CB & Ham Lingo
Modification List
Click on Modification List and it has all of the information you seek.
Lon
Tech808 |
Tech548
Moderator
Username: Tech548
Post Number: 307
Registered: 5-2004
| | Posted on Tuesday, October 05, 2004 - 11:45 am: |
|
1861
Here's a little more information that may help also.
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Mic circuit changes:
1. Unsolder banded end of diode D-21 and lift up.
2. Unsolder banded end of diode D-22 and lift up.
3. Solder a 4.7 k resistor across where D-21 and D-22 was unsoldered.
4. Replace R-78 (27k) with a 56k.
5. Replace R-84 (4.7k) with a 2.2k.
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Transmit Circuit:
1. Replace C-174 (56pF NPO) with a 82pF NPO ceramic capacitor.
2. Replace C-173 (180pF NPO) with a 220pF NPO ceramic capacitor.
3. Re-tune coils L-32, L-30, L-29, L-28 and VR-8 for maximum forward A/M power.
-------------------
Clarifier Tracking:
1. Unsolder and remove D-30.
2. Solder a jumper across D-29.
3. Cut the end of R-119 that is closest to D-29.
4. Solder a jumper wire from the cut end of R-119 to the banded end of D-44.
5. Follow the PURPLE/WHITE wire form the clarifier control to the PC board and unsolder it.
6. Resolder this wire to the PC board ground.
7. You should now be able to slide 1Kc up and about 3Kc down.
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10Khz Switch for 858 SSB:
1- Cut the track that goes to pin 13.
2- Put a 4.7 K Ohm 1/4 watt resistor across the cut.
3- Now install a SPDT (center off) toggle switch.
4- Wire the top pin on the switch to board ground.
5- Wire the middle pin on the switch to pin 13 on the PLL.
6- Wire the bottom pin on the switch to a constant supply voltage that is the SAME AS THE PLL PIN CONTROL VOLTAGE.
Note: The (A) Channels will be as follows....
For Channel 3A, go to CH 4 and flick the toggle switch down.
For Channel 7A, go to CH 7 and flick the toggle switch up.
For Channel 11A, go to CH 12 and flick the toggle switch down.
For Channel 15A, go to CH 15 and flick the toggle switch up.
For Channel 19A, go to CH 20 and flick the toggle switch down.
--------------------
Varible Adjustments:
Modulation: VR-7 or cut D-23
A/M Power: VR-8
SSB Power: CT-7
RX Coils: L-3 thru L-8
TX Coils: L-32, L-30
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858 SSB Chassis Talkback
The Cobra 138 and 139-XLR SSB radios have a relay in them. To get talkback, install a .01uF ceramic capacitor from pin 10 of IC-4 to the speaker positive lead.
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Here are a couple of known Bugs in the 858 SSB Chassis:
1- The A/M regulator 2SC-1419 is weak. Unsolder it and replace it with a GE-66, ECG-152 or a NTE-152.
2- If relay buzzes on SSB, no A/M transmit, lights go dim, or possibly the fuse pops, replace C-179 (a 2.2uF 25v tantalum cap located near finals) with a standard 2.2uF electrolytic capacitor. PAY ATTENTION to the + and - polarity.
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Personally, I have always loved this particular circuit board layout. It was one of the best ever designed. This radio has the capabilities of over 200 channels when set up correctly. No other CB board design could ever hold a candle to it and that includes todays CB's. This radio is a classic and can still strut its stuff.
Jeff
Tech548 |
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