KB2LJJ                                                           
 Home                               Radio Mods Database and Manuals
 





 

Cobra 148 GTL

MB8719/8734 Deluxe Dual Conversion Chassis

 

Adjustments

L38
TR24 = AMC
VR11 = ALC
VR10 = AM PWR
Note: If the ALC has been clipped, its best to restore it.
TR24 is a 2SC945AO

 

 

Clarifier Modification

1. Remove D52.
2. Lift the hot (orange) Clarifier wire from the board, and connect to pin 3 of IC4 (MB3756).
3. Slide range can be increased by jumpering or lowering the value of R174 or R175, or both.
4. Varctor is D35. Adding a 5.6uh coil to the anode will also increase slide range further.
 

 

Option 2
(Increases tuning range to approximately 14khz) 1. Remove D52.
2. Lift the hot (orange) Clarifier wire from the board, and connect to pin 1 of IC4 (MB3756).
3. Clip or remove R44.
4. Center Clarifer control and realign the radio
 
RF Amp Mod.
TR17 is a 2SC1674. Its a high noise package.
Changing TR17 to a 2SC2999 offers higher amplification of weak signals, and low noise.
Re-Adjust L4 and L5. The gain will improve more than 6db with the same signal to noise ratio.
 

 

 

New Cobra 148GTL-B (Cybernet PTBM122DOX Chassis PLL02A)

L9
L16
RV14 AMC
RV13 SSB Mic Gain
RV5 ALC
RV15 AM PWR
 

Clarifier Slide

1. Remove D7.
2. Remove the hot wire (+8VDC RX-Only) from the board and connect instead to the emitter of Q28 main voltage regulator.
3. Slide range increased by adding 5.6uh inductor in series with +end of varactor D5