matching FETs

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buschfsu

Well-known member
Joined
Dec 31, 2004
Messages
760
Location
jacksonville FL
i have a radio shack meter with a transistor checker (holes labelled ECBE) to measure hFE (Gain). Question is can i use this to measure a FET for matching purposes? where would the C,E, B need to go?

thanks
jason
 
[quote author="gyraf"]Nope. Make a forum search for info on matching fets.[/quote]

Or get a Curve Tracer.
 
[quote author="analag"]Or get a Curve Tracer.[/quote]

That is a waste of time and money for JFETs. Curve tracing is very well justified to find good tubes for varimu cells though.
Build the simple Forssell jig. Idss matching is enough 99% of the time. Vgs matching measurements are just as easy and needed for low offset requirements only. Designs that require "perfect" JFET matching are poor since FET parameters are all over the place to begin with. Don't use designs that require that. It is like trying to use tubes in high current switching power supplies.
You will get a lot of even harmonic cancallation anyhow, leaving you with harsh odd harmonic distortion.
 
Jason,
A couple threads I found in my bookmarks to get you started:

http://www.groupdiy.com/index.php?topic=1766&start=0&postdays=0&postorder=asc&highlight=hamptone

http://www.groupdiy.com/index.php?topic=4531&highlight=matching
 
I just ordered 2 of the 1176 new design boards & haven't read the GIANT thread yet & was wondering if I may need to match the FETs for that project also :?:

If so, thanks for the links.

Kevin
 
[quote author="khstudio"]I just ordered 2 of the 1176 new design boards & haven't read the GIANT thread yet & was wondering if I may need to match the FETs for that project also :?: [/quote]

I think PRR suggested a test circuit for the 1176 somewhere here, which basically rebuild the 1176 damping section and used a pot to supply the control voltage for the FET from a battery. I measured the control voltage for a damping of 1 and 10 dB and selected the closest matches for the gain reduction FETs for stereo pairs and the 2nd closest matches for their gain reduction meter FETs. I got FETs for 10 units out of 100 FETs I measured, but haven't finished the units yet, so there is no sonical confimation yet. But I feel very comfortable with that method, because it basically does, what happens in the real unit anyway.

Michael
 
field effecft transistors are very cool devices, unfortunately, they fall between the crack of a good vacuum tube and a bjt.
nary the twine shall, meet.
numerous people have tried endelessly to get hhe warm tiube sound with nomdistortion but it dois not happen, so eother go, tiubes or solod stae for besu sound.
 
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