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JC Penny'6247 power or variable swing mod
- Thread starter Harley3315
- Start date
Don't have Sams CB226 handy, but I remember at least one JCPenney sideband CB that had the final bias turned off in AM mode through the mode selector. The fix was to find the wire feeding bias current to the final, take loose the far end and connect it to the transmit-only power so the final would have bias in all modes, not just SSB.
Might be remembering the wrong model, but the symptom rings a bell.
73
Might be remembering the wrong model, but the symptom rings a bell.
73
Pretty sure I have that on file. Same as what we used on the GE Superbase model. Different circuit boards, but the same AM modulator setup.
It's all about the circuit-board ID number. I used the schemo for a PTBM-058COX radio.
It requires a NPN Darlington transistor and some resistors to take the place of the 10-Watt rheostat. Pretty sure the best resistance value for the carrier control is 1k, though a 500-ohm works. A higher resistance will crowd the control's response at one end of the knob's rotation.
Found a diagram on my ImageShack. Yay!
So, "Yellow wire" or orange for the Superbase may be another color in this radio. The diagram says nothing about this.
If you key the radio on AM, the DC voltage on the two lugs of the fat white rheostat will show different readings. The wire with the higher voltage takes the place of "orange" on the schemo. Comes loose from the old control. Goes to the Darlington collector and to the wiper of the carrier-control pot. The one marked "Yellow" or whatever color is on the rheostat's other lug will go the transistor's emitter.
And where it says "D23", that same functional diode in your radio is D43.
You'll need a surprisingly-large aluminum heat sink for the carrier-control transistor. Bolting it to the steel chassis deck alone won't quite do.
That's the gist of it for these old Cybernet-made radios.
73
It's all about the circuit-board ID number. I used the schemo for a PTBM-058COX radio.
It requires a NPN Darlington transistor and some resistors to take the place of the 10-Watt rheostat. Pretty sure the best resistance value for the carrier control is 1k, though a 500-ohm works. A higher resistance will crowd the control's response at one end of the knob's rotation.
Found a diagram on my ImageShack. Yay!
So, "Yellow wire" or orange for the Superbase may be another color in this radio. The diagram says nothing about this.
If you key the radio on AM, the DC voltage on the two lugs of the fat white rheostat will show different readings. The wire with the higher voltage takes the place of "orange" on the schemo. Comes loose from the old control. Goes to the Darlington collector and to the wiper of the carrier-control pot. The one marked "Yellow" or whatever color is on the rheostat's other lug will go the transistor's emitter.
And where it says "D23", that same functional diode in your radio is D43.
You'll need a surprisingly-large aluminum heat sink for the carrier-control transistor. Bolting it to the steel chassis deck alone won't quite do.
That's the gist of it for these old Cybernet-made radios.
73
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