Regarding R.G's transistor testing article

[modmod]

after testing 20-30 resistors,the closest one i found are 2.471ohms carbon film and 2.490ohms metal film,which one should i use for R.G's ge tansistor testing project ? will carbon film affects the result also in +/- 5% ? thanks :?

[Fret Wire]

Use the resistor closest to the spec, which would be the carbon film. Or...your thread is back at the top, and hopefully someone with the right answer will read it. lol :twisted:

Seriously, how hard would it be to build one in a plastic enclosure with LED read outs for gain and leakage?

[saros141]

Yep, go with the 2.471 KILO ohms, that should do fine.  Ambient temperature fluctuation probably has a bigger effect on accuracy and repeatability than that 1 ohm difference.

AFAIK if you're measuring them you don't need to worry about the tolerance.

The LED readout idea sounds cool - you'd hafta put a circuit in there to do the math for the leakage though, if you wanted it displayed in microamps...

[Fret Wire]

Yeah, the rest would be easy. Radio Shack plastic box, socket for the trannie, jacks for the DMM leads, switch. The LED read out would be really nice.

[Fret Wire]

No takers? A tranny tester with LED read outs for gain and leakage? How's this for imagination: A dedicated tranny tester with regular LED's. Say a Rangemaster. A set of red and green led's for leakage and gain. You set the parameters for each, say 75-85 for gain and under 300 for leakage. Put the tranny in and if it meets the parameters, the green led's for both light up (pass). If either the leakage or gain is over or under your parameters, you get a red led (fail). After all, if it's within specs, the actual gain and leakage numbers doesn't matter since you set the bias by voltage readings. Kinda like a complicated cable tester.

[RobB]

If you don't mind a bit of algebra then it doesn't matter too much.  Just measure your resistors, DC supply etc....  Set up equations with your values in a spread sheet and plug in your measured voltages.  The math is supplied in RG Keen's fuzz face artical.  

I still have my germanium test jig and matching spread sheet.  It was almost as interesting as building the fuzz face.