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AC128s and help with TESTING TRANSISTORS...


 
1/6/2003 5:05 PM
Ian Anderson
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AC128s and help with TESTING TRANSISTORS...
Anyone tried the AC128s available from www.farnell.co.uk ???? If so, did you find 'em to be consistently low leakage/highish gain?  
 
Also, am I doing this right? (testing for Hfe and leakage using the tester at www.geofex.com), for example...  
 
* 0.523v measured across 1k5 resistor *without* voltage applied to base (523mA leakage?)  
 
* 1.245v measured across 1k5 resistor *with* voltage applied to base (523mA leakage?)  
 
* 1.245 - 0.523 = 0.722 (Hfe=72)  
 
Does this look right? - I seem to be getting loads of AC126's with around 400mA leakage and a gain (Hfe) of around 60.  
 
 
... Ian :)
 
1/6/2003 5:08 PM
griff
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yeah, i bought a bag of ten ac128s, never did any real testing on em, but pligged em in my multimeter and they all seemed to be reasonably high gain and bias in to a pretty nice tone on my lil fuzzface with bias control.  
 
But then, i might've just gotten a good batch..  
 
griff
 
1/6/2003 7:21 PM
Bernt
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No, it does not look right. It seems your'e in the 30 ľA-range, if my math is correct (have'nt had my coffee yet...).  
Bernt.
 
1/6/2003 7:36 PM
Ian Anderson
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Bernt,  
 
Can you describe the process - it seems it's the maths part I'm getting wrong (unsurprisingly)  
 
... Ian :)
 
1/6/2003 8:36 PM
Bernt
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Ian!  
I was wrong too! (Got to get that coffee...). I (tried to) use Ohm's law: (U/R=I) 0.523V/1.5kohms = 349 ľA. And I assumed you connected the resistor in series with the Collector-Emitter (Base open).  
Yell at me if it's unclear; I'm known to have been wrong before ;) . Somewhere there's a site with good instructions how to measure gain in Ge-trannies... I'll be back.  
Regards, Bernt.
 
1/6/2003 10:10 PM
Mike Burgundy
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Check out RG Keen's brilliant article on GEO (it's on the reading list) for theory and how-to's on testing trannies.  
The batch of Farnell 128's I got were Checg production (high thin top-hats) and leaky as hell for about 80% to 90% of them. Not worth the trouble.  
A lot will work with more or less reasonable tone though, just not good.
 
1/7/2003 4:05 PM
Ian Anderson
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Burnt/Mike,  
 
I've checked out RG Keen's transistor page at Geofex.com, but I'm still not quite sure if I'm doing this right.  
 
Anyone?  
 
... Ian :(
 
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