CB to HAM Radio Conversions


Amateur Station
Picked up this practically new Cobra 138, no scratches anywhere. Someone had installed it in a vehicle back around 1972 or 73 then didn't really use it much. They put it back in the box with all accessories except for the power cord which I found. These things were classic. I'm going to connect the Para Dynamicics counter on top to it's VCO output point.


Then I also found the old PAL VFO (11 Meter Slider / Scanner) for it below. You know how CB'ers were with their misinterpretation of the terms and definitions along with the ones they simply made up. They even called small low power RF linears, modulators. However, this one is the correct A-1 model for the 138 and the 139 base and the things were designed and constructed really well. That's the thing about a lot of these old CB radios and their accessories from the early and mid 1970's is that many of them worked and sounded better on AM and SSB both when modified for the ham bands than the higher priced amateur junk being made at the time and even now. I have not cleaned up and gone thru the PAL VFO yet, but I've cleaned and aligned the 138 and removed the two limiter diodes, D40 and D41. I might install some type of a processor/rotator board at the mic input. I might also try to find an old 139 base in the same condition and use the VFO on that instead. It's a little late though with the sunspot activity pretty much gone now for 10-meters, but it's something to play with and keep nevertheless. There's always 12-meter conversions too, but that may not be much better than 10 right now. I even modified one many years ago for 15-meters, but it was a lot more work. It can be done though.



Amateur Station
Decided to open up the PAL VFO again and as I stated they were designed and built really well. They have very slow and weighted gear reduction too and this one still has a solid output and in the correct place, but that filter cap and maybe the 3 diodes should be replaced.


Then the main oscillator board below. All you had to do was change that one xtal down in the bottom left hand corner of the board to shift the whole thing up. Then sometimes you had to change 2 of the coils too which you could order from them along with the xtals, but that was more than 40 years ago. I played around with a few of them back then and they worked better and were more stable than most ham VFO's were. People today say you need a DDS VFO, but in this case, I fully disagree. These things use to make the old tube CB's like the Courier 23 for example, rock solid on frequency.


Then here is the back showing that it's the A-1 model. These things were the easiest way back then to make the old xtal 23 channel radios slide up to 10-meters. You just needed a frequency counter, xtal and a few component changes.


Then here is the PAL VFO schematic below. A very nice and stable design with a mixer, driver and a buffer output stage with an adjustable level .


And then the actual PAL VFO engineering notes below for the component values in each of the models they made.



Amateur Station
Picked up another one of the PAL VFO’s dirt cheap for $30. It’s one of the higher letter models with the higher frequency coils.