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View Full Version : Iím new here, just got these feet today.



Spooky
12-20-2021, 01:29 AM
Hey I’m glad to be here I’m hoping it’s a place to share cb radio experience, information, and encouragement. I’m mostly interested in learning to repair barefoot radios. I have some cheap chi-com equipment; LCR Tester, Handheld Oscilloscope, Fluke DMM, Dosy Meter for measuring Dosy-Watts, and a home brew dummy load, by no means a full workbench. I’m an OTR driver and I fix a few radios in the sleeper then a few more when I’m home. I’ve refurbished Cobra 29, 25, Uniden 68, 66, my current project is refurbishing a Realistic TRC-421A which I cannot find a roadmap for it or a service manual. I’m also looking for a Cobra 19 DX iii. Only that model NIB please. I’ve been using Fairchild 13N10 Mosfets as replacement final transistors but I’m interested in a legit source of genuine BJTs as I find them more SWR tolerant. Have fun letting the smoke out!

Bobcat
12-20-2021, 10:22 AM
Welcome in Spooky!
I just checked my only two resources and could not find a thing on that 421A. Looks like SAMS never got around to it.

I've always been interested in the idea of MOSFET replacements for BJTs that can't be found any more...but just haven't "chased into it" far enough yet. As they are used in a number of ham transceivers... I'd like to think that there is a safe way to do it..... hopefully I will find out one day.

Anyway... welcome aboard!

Spooky
12-20-2021, 07:06 PM
Thanks for the welcome and for trying to find that schematic.

I’ve been using MOSFET finals as replacement transistors for a few years starting with in IRF 520 and now a batch of Fairchild 13N10. I only buy my components from mouser or element14 online supply houses I feel like they sell the genuine product. I’ve found more fakes on eBay than genuine articles and very poor QA. Just check your gate voltage and adjust it with a resistor if necessary, other than that you can swap a mosfet for a bjt normal procedure. I always finish with a final tank circuit alignment afterwards. The only bug thing to consider is they are more SWR sensitive. I find they’re happiest at <\= 1.2:1 or better. BJTs on the other hand I have no worries installing them to a 1.5 SWR. I come from land mobile and commercial paging world where everything had to be 1.1 or better or else and I kind of try to maintain that standard. I’m a firm believer that the antenna network is the most important part of a CB radio system. Enjoy the static.

Spooky in the top left corner.

Spooky
12-20-2021, 07:23 PM
We should probably put further posts in a new topic thread regarding mosfets etc.