Chris wrote:
Maybe somebody here can answer my question. The MS1307 is a MOSFET used in
several HF amplifiers. All the ones I've seen have the numbers filed off. It
is rumoured that these are just IRF520's with the numbers removed. Has
anyone else heard this?

This page thinks so:

http://www.xs4all.nl/~barendh/Cateng/Cateng_fet.htm

25W HF power is not out of the question for an IRF520 @14V.
I used to get 40W on 20m out of IRF510s, the IRF520 probably
has less gain than the IRF510 but more power-handling ability.

Dana