Cb radio cobra ltd 29 with mosfet's?

Question

Have some one tryed this I want to take out the 1969 final out of my cobra 29 and put in a irf520 mosfet's will it work i know it works in some of the galaxy radios so will it work in my ltd29 if so how tell me i have four 29's

Answer 1

Try it - I may or may not work. One thing is sure - you will not gain any more power. The present base drive is specially tailored re proper base current for the final.

The only thing is - mosfets stay cooler because of the lower Source/Drain "ON" resistance. You must have a power/SWR meter to check, compare.  A spectrum analyzer WOULD help to see how dirty your signal really is or has become with the Mosfet installed....... I would stick with the old 2SC..... 2SD type RF finals. The IRF 520 may have too slow a rise and fall time to be of good use. You need at least a 10ns rise AND fall time (square wave pulse test set-up) for them to be efficient. That would JUST get you to 30MHz.

I wish you luck

Electronic tech for 30 years.....

EDIT:  you are out of luck there.

Best rise time = 30ns (nano seconds)

Best Turn-off Delay time = 19 ns

Best Fall time = 20 ns

So - you have a total of 70 ns to deal with. 1000MHz divided by 70ns = 14.2MHz Max frequency..... and you need a comfortable flat transmission bandwidth of 33MHz at least.