TRANSISTORS: RG Keen, Germanium Transistor Test Method

If you haven't heard of this before (which seems unlikely), here's the original RG Keen article, which explains how it works.  I use a spreadsheet set up with the calculations ready to go for testing; there's also an online calculator here.

NOTE:

• Be prepared to see the voltage fluctuate a lot while the transistor stabilises.  Don’t wait too long though, as you will be there forever - it may never stop!  

• Handle the transistor as little as possible with your fingers, as the heat will transfer

• Different environments will provide different results - this is very temperature dependant.

• With all methods, the test results will vary, depending on the method used.  Why?  Without attempting to explain the math that I don't fully understand, hFE varies with the current applied to the base.  Different methods apply different currents, so results will differ.

RG KEEN METHOD FOR TESTING GERMANIUM TRANSISTORS

LEAKAGE TABLE FOR RG KEEN METHOD

If you just want to know how leaky the transistor you’re testing is, here's a quick guide (numbers have been rounded for ease of use).  This only applies to the RG Keen method.

VDC        LEAKAGE - uA

0.1           40

0.25         100

0.5           200

0.75         300

1.00         400

1.25         500

1.50         600

1.75         700

2.00         800

TESTER BUILD

I recently purchased a small multi-function tester, and while it's great for so many different measurements, I wasn't completely happy with the leakage results on germanium transistors - maybe it's just not what I'm used to...   

I've been using a tester that I built using a layout from Guitar FX Layouts  and while it works, it's very small, and I found that the transistor socket got a bit loose over time.  It was just a bit fiddly for me.  

So today, I built something a bit more robust from some scrap 0.15" vero, I kind of worked it out as I made it, so the layout below is not an exact match.  

• Pins to insert in a breadboard rather than use a socket

• The switch is mounted through the board, and I used a trimmer for biasing the collector

It's not the best-looking thing I've ever made, but it feels solid, and it works as intended.  I wish I had more colour options for the wires and shrinkwrap to make it easier to identify the leads, but it's not the end of the world.   I might even get around to mounting it in an enclosure one day with a small breadboard attached.

This is a rough layout, not identical to the one I made, but you get the idea.  

NOTE:  

• This is specifically laid out for PNP germanium transistors; if you want to measure NPN, reverse the polarity of power and the multi-meter

• Components must be as close as possible to the values provided to provide the most accurate results (including voltage)