jfet matcher

[darrylportelli]

hey Im gonna do a jfet matcher as listed here: http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/JFET_Matcher_LAYOUT.gif.html
my question is does it matter where toy connect the multimeters probes on those DMM tracks, is one for positive and one for negative? im guessing that the one which links to the capacitor linking to ground is -ve.
thanks

[frequencycentral]

I use R.G.'s Improved JFET matcher: http://www.geofex.com/FX_images/fetmatch.gif

It shouldn't really matter how you connect the DMM probes, because as long as you're getting readings you can match. You'll easily suss out which way to connect the probes - I forget now, I'd have to breadboard it again to remember!

[darrylportelli]

10x mate will breadboard it to match a little jfets.

[darrylportelli]

Would 10 FETs be enough to match a quartet? and when you match them are you actually measuring their gain?? 10X

[R.G.]

Unfortunately, there is an element of luck involved. The best thing is if you're buying from a shop directly and you can wheedle them into letting you match up a quartet there in the store. Otherwise, you're simply going to have to buy enough to get lucky. It's a guess.

My personal guess is that 10 is a bit low, but I'd be comfortable with 20. Notice that many sellers make it much cheaper per device if you buy bigger lots. You may find that 25 or 50 are not much more than 10. It all depends on who you buy from.

And your luck that day. 

[frequencycentral]

I bought thirty 2n5485, and got three matched sets, which I thought was pretty lucky. Chances are if you just get ten you won't get a matched set of four. Life's like that. 

[darrylportelli]

hey RG 10x for the Idea.....Ill try and lure the shop guy into letting me match them at the shop...I doubt it but hey maybe the guy wants to get into heaven who knows!!! If not 20 it is

[R.G.]

Here's an idea. Ask the shop owner when it's least busy in the shop, and tell him you'll pay him twice as much per selected JFET as for an unselected one. You come out ahead and so does he.

[Mark Hammer]

That's probably a good idea.  I once tried arriving with my matcher in hand and started working my way through a bin.  The owner started waving his hand and shouting "No, no, you just buy.  No test!".  The flaw was that I didn't appeal to his more mercantile nature first, before commencing.

[DougH]

I think I have a batch of 25-30 J201's at home. I found 2 or 3 matched sets of 4 in the group. They worked great for the Phase90 I built. The others can easily be put to use too. If you buy in quantity, they are not very expensive.

[darrylportelli]

Hey I have j201's at home about 45 cos I ordered 50 and used some of em but I was told that their a bad Idea for phasers....anyways I ordered 25 2n5952 from smallbear today.
Btw could someone tell me what excactly do you match in the trannys,do you measure gain? cos my friend has a nifty gadget that tells you which pins are dsg or bce, it tells you the gain and a lot of other useful stuff about the tranny you put in it, its a preety neat piece of equipment and I need to know exactly what value I need to look for in order to match them with it.
Thanks 

[frequencycentral]

Btw could someone tell me what excactly do you match in the trannys,

I use R.G.'s Improved JFET matcher: http://www.geofex.com/FX_images/fetmatch.gif