Transistor confusion.

[Casey4s]

I am not a SS guy at all but I am working on a Reverb pedal and all indications are that the output transistor is open at the gate, How do I make sure?

It's a JFET J201 N channel.  All I have is an N channel MPF102 on hand( rat shack). Can I swap this for the J201 or not?

If not where do I look for the proper FET?

Thanks a bunch guys...

[J M Fahey]

*Might* be, depemds on how it's used it may matter or not.
Please post a schematic, at least a hand drawn one of that gain stage and what feeds and loads it.
Does it amplify or is it just a simple buffer?
How is it biased?

Are you sure that gate is open? you should measure a low value (100/500 ohms) Drain-source, both ways, and a diode from gate to any of the others.

[Casey4s]

*Might* be, depemds on how it's used it may matter or not.
Please post a schematic, at least a hand drawn one of that gain stage and what feeds and loads it.
Does it amplify or is it just a simple buffer?
How is it biased?

Are you sure that gate is open? you should measure a low value (100/500 ohms) Drain-source, both ways, and a diode from gate to any of the others.

LOL... I am not sure about anyof this, I am a Tube guy. But I am getting 0v on that gate. The other JFET has voltage.

This is a MOD kits Reverb unit, and the JFET in trouble is right at the output. I can get verb up to that Jfet but not out. So as a SS Novice I am assuming this is the trouble. I just ordered 2 of the J201 JFETs so I will replace it and see if I was right. 

But be prepared for me to be right here soon LOL...


I will draw out that portion of the schematic and post it soon.

Thaks for the help.