Many people have used an MPF102 as a
replacement. I tried it on mine and found that
it worked, but had about half the sensitivity of
the original.

The original is a 2SK152 Data can be found he
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm

The replacement is a NTE312.

I scored a VHF FET from an old 46/49MHz cordless
phone, and used that. There was one drawback to my
substitution, The pinchoff voltage is different, and the RF
gain control has no effect. Therefore, the gain is set
wide open, since you cant bias the FET off. I cant
remember the FET number.

The good point is that sensitivity is hotter than with the
original.

Add a pair of 1n4148/914 diodes back to back across the
antenna jack to eliminate this problem in the future.

YMMV - Good luck