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Don't buy AC128s from Farnell UK!!

6/19/2000 9:07 AM
Don't buy AC128s from Farnell UK!!
Hi All,  
Thought I'd turn my silicon fuzz face into a real one at the weekend. Bought 4 AC128 from Farnell, got the two that had the closest to recommended Hfe and slung the circuit together. It sounded so bad that I assumed I had made a mistake on the stripboard (broken motorboat noises).  
As an experiment (after 2 hours of looking for my mistake!) I stuck a pair of PNP silicon transistors in the circuit, and it sounded OK (for a silicon fuzz face).  
So if you're in the UK and want Germaniums - don't be tempted by the new production AC128's at RS and Farnell - you'll be wasting your money, and they're not cheap.  
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6/19/2000 12:18 PM

Yeah, I tried some of those. Same result as before with the AC128 - only about one in three (or four, or five!!) are usable. I have pile of them that I use for germanium diodes by just using the collector and base. Otherwise, they're useless.
6/19/2000 4:37 PM
Ian Anderson

How can you tell these from the good ones if you were to look at one? ...on-body markings etc...  
There is a place up the road from me where I get my AC128 (well, everything really) and would like to know if these are the 'tainted' ones.  
... Ian
6/19/2000 8:36 PM

The last lot I got from RS were crap too. They have a tall & fat, shiny silver body and a red dot to indicate the collector. The older ones, which were OK, have a thinner, dull metal case and a tag to indicate the emitter.
6/20/2000 11:00 AM

I got 2 older ones and 2 newer ones. They were all crap!
6/20/2000 12:01 AM
I haven't found any non-tainted ones. I count on between one in three and one in five to be good. This matches the stories I've heard about original production, so I think it's par for the course.  
The good ones do sound OK, but there's a high fallout.
6/20/2000 11:07 AM

After a bit of digging around at work I found some NKT163 and NKT164. The closest to the required Hfe I could find were 84 and 85. I've fitted them but although the unit now sounds pretty good, it's not fuzzy enough!  
Would you recommend I change the resistors to get a bit more gain - or try to get some more suitable transistors? I'd buy some from you, but I'm waiting until all the things I want from you are in stock before I place an order. Since I'm in the UK I don't want to pay for more than one lot of shipping costs.  

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