cobra 139xlr

[rumblefish]

I'm attempting to install a receive kit in this radio. upd858 chip. board number is PC-176AB. I believe that tr-5 is the rf amp to replace with the 2sc2999. I'm not sure about the noise blanker diode numbers or the am detector diode numbers that are to be changed to the 1n6263's. If somebody has the info it would be very much appreciated. thanks steve

[Rick]

Tr1 is the RF-Amp and the detector diodes are D13/14 and 15.

Rick.

[rumblefish]

I think tr-1 is a 2sc945. it is not replaceable with the 2sc2999. isn't tr-1 part of the noise blanker circuitry? I will replace the diodes mentioned and post results. thanks for the help rick. steve

[Rick]

My error I was look at the old diagram, now I have check out the right one you are right TR5 is the RF-AMP (2SC1730) the worth changing are D10, 11, 15 and D16. Diodes which are type 1N60 maybe changed for 1N6263 as there are a lot faster.

Rick.

[rumblefish]

thank you for the speedy reply rick!! I've replaced the 1730 with the 2999.the improvement is quite noticeable to the ear. 1-s unit receive gain on the cobras meter. fringe stations are readable now . now its time to replace the diodes. thanks steve.