Transistor testing/selection : how?

[timmyo]

Is there any info or links hereabouts about how to test transistors for gain and leakage? Is it do-able with basic kit?

[R.G.]

Read http://www.geofex.com

[sean k]

I've got to o some soon, matching npn silicons for a synth circuit, and I've got the matching diagrams somewhere but the part that was stressed to me was that early morning is the best time as the temperature is fairly constant and not touching the transistors to be tested as body heat can throw them right out. Apart from that the testing for leakage and stuff on germaniums is on the geofex site somewheres.

[timmyo]

Read http://www.geofex.com

Thanks - found your 'Technology of the fuzz face' page which has this info on

ta

Tim

[R.G.]

I've got to o some soon, matching npn silicons for a synth circuit, and I've got the matching diagrams somewhere but the part that was stressed to me was that early morning is the best time as the temperature is fairly constant and not touching the transistors to be tested as body heat can throw them right out. Apart from that the testing for leakage and stuff on germaniums is on the geofex site somewheres.

If you're matching for a synth application, you probably are matching Vbe at 1ma of collector current. That's something more like the circuit for testing JFETs than the gain/leakage for germaniums. Although you may want to match for gain too.

[JDoyle]

If you are doing something for a synth app, you may want to consider the time saved vs. the extra cost of picking up a precision matched pair like the LM394 - they are made by fabricating a number of transistors at the same time, making them as identical as possible, and then paralleling them to both average out the slight differences and also to reduce noise.

Linear Systems also makes some duals that are specifically designed for 'log conformance' - which is exactly what you are going to be looking for in synth applications...

Good luck!

Jay Doyle