Determining the type of old Gibson transistors 1970's

[malkmus]

Greetings,......I am repairing the circuit board on a 1970's Gibson electric guitar. I've determined that one of the transistors is bad. I have tried to cross-reference the part on Mouser and Digikey's websites....with no luck. Does anyone have a good way of determining what this part is and finding an adequate replacement. The markings on the device are SF 51234 then 802 underneath.....the circuit board indicates the position for D S and G. There are a number of these on the board. I tested a couple of the others in my multimeter....they seem to measure out with a gain of 970 on the PNP setting. ....hopefully I've done this correctly! Any help would be greatly appreciated.

John

[bulldogguitars]

What exactly is the board out of?

[Enzo]

The numbers are house numbers and won't show up in catalogs.

The DSG - drain, source, gate - on the board indicates it is a JFET. You'd have to determine N or P channel from voltage polarity. If your tester covers JFETs test them that way.

Most any general purpose JFET ought to work, I'd think, assuming correct polarity.

[malkmus]

....the guitar is a Gibson RD.

I will test the polarity and see if it is N or P channel....PNP on the multimeter isn't = P channel FET?

Thanks for the replies.

[frank.clarke]

If you don't know whether the pcb drain is positive or negative, how do you know the transistor is bad?
If it is a gain stage you would probably need to bias it anyway, so you could probably get a J201 to work. Hard to know what the gain/transconductance of the original transistor was, regardless of markings.

[52 Bill]

The RD Artist Schematic shows them as N-Channel jfets. It also states that they are "selected" components.

How have you "determined that one is bad"?

What model RD guitar, and what's the problem?

[malkmus]

....I had originally determined/found the bad part by testing the voltages with a multimeter....the bad one seemed "off" in relation to the others.

I tried the J201 in its place. It now works beautifully!

Thanks for your help.

John