NEC FM Transmitter F300DHF IPA Repair - MOSFET Replacement

[Oddcoffee]

Hi all,

On my bench currently is a F300DHF IPA from a NEC FBN series FM transmitter. The main power mosfets test crook and i'm having absolutely nill luck trying to source some replacements as they're no longer manufactured. I can't seem to find equivalents or substitutes, even. The best I can find is supposedly NOS stock with no info on HK inventory and alibaba (no thank you). Part number is 2SK524.
The data sheet doesn't give me much to work on although the basics are there (attached), was wondering if anyone can point me in the right direction?

Cheers,

[dave_k]

Those NEC transistors are basically unobtanium! My suggestion would be to gut the IPA and replace it with a BLF278 300W FM pallet.

I have performed a similar modification to a 600W IPA module from a NEC FBN-11K20E transmitter.



The module is preceded by a 6dB pad (to match the output level of the exciter better to the input level required by the pallet). The original circulators were removed as the pallet will tolerate a 3 to 1 load mismatch, however the original reflected power alarm circuit was retained, which controls the bias supply to the pallet.

For added protection a shorted 1/4 wave stub was also added to the input of the tube cavity, to prevent any tube flash overs from damaging the pallet (it acts as a DC short, but is transparent at FM frequency).

Here is a link for a suitable 300W pallet:
http://broadcastconcepts.com/BLF278-300W.html