re-replacing 2sk213/j76 transistors help

[NRJohnson]

hello diy'ers.

i have a belles research model 55 preamp. she works great after repairs, however it has had a transistor swap previous to me owning it.
it should have had the 2sk213/j76 to220 transistors but instead they used the irf mosfet in soT23 packages.
i have obtained 4 pairs of the j76/213 pairs and am looking to restore this baby.
anyways, i dont have a schematic, but if anyone could help walk me through this id be grateful.

the spots for the transistors on the board only has 5 pin holes, and the transistors have 6 legs total. plus i have no clue as to which way they should be facing. i do see that the pin out on the two types of transistors is close enough to work, but one of the pairs is under the board and the other above.

im sure i can match the pin outs of the pairs, but im not sure what to do with the extra leg.

thanks for any and all help,

the jerk

 

[ticknpop]

Take some close up pictures of the board where the fets go.

 

[RM]

Belles 55 preamp

Look here. Maybe you can be helped by these pics.

thoughts on Belles/OCM 55 preamp? - AudioKarma.org Home Audio Stereo Discussion Forums

Regards
RM

 

[NRJohnson]

i will take pics. maybe you guys can decipher the way they are supposed to mount.

thanks for the link to Ak, but my 55 is a pre ocm Belles Research model. no black gates, 1/2 the transistors, only one board, no record potentiometer.

my amp is the ocm 200 however.

 

[NRJohnson]

ok heres a shot of the top of the board.

you can see the IRF mosfets on top and then the others mounted under the board with the legs sticking up. i will take apart the pre to get the bottom if necessary.

the irf 9120, and irfd1Z3 are top mounted. the pinholes seem to accept either the mosfets in now, or the to220 as there is a trace to the ground from the unused hole on all 8 mounts.

anyways heres the pic, what do you guys think?

 

[NRJohnson]

of course in answering my own question of how they are mounted, with the small trace off the unused pinhole, i guess which mosfets would you guys replace with which ones?

also on this board, the middle is the amp section, the right is the power supply, and the left is the phono. there is switches for loading and MM/MC. no schematic makes it all a big guessing game however. thanks for looking.

 

[NRJohnson]

more research yields.....
j76 -p channel
213 n channel

irf9120 p channel.
irfd1z3 n channel


so id swap the comparable channels for each other. this is assuming a lot, assumptions being the mother of all F ups, can someone say yay or nay? id rather not fry expensive unobtanium.

 

[NRJohnson]

in the spirit of diy, i just said the hell with it and toast or not im going to try it. it worked. i lined up the drain to the ground, and she is alive.

im not sure if the board was like that with the space for hexfets, or if someone modded it to fit, but its cool that they made it work. i made it back to original. sounds much less forward, and now the soundstage has depth again. i just needed to write down my thoughts and i figured it out. thanks.