Roll your own transistor tester

Can’t remember exactly why we needed this. I think it was an Vintech 1073 that came in with a strange clipping issue. Long story short, it appears that somebody in the QC department at AMS might have been hungover or colorblind, as one of the collector resistors on one of the BC184 NPNs was off by a factor of 10…or maybe it was 100. Either way; a lot. Once I find the pictures from the repair session, they’ll go up in another blog post where you can see the crazy scope trace.

But in any case, when we thought the problems we were seeing might lead to the necessity of replacing transistors, we realized it would be a treat to be able to match across channels. This would be easy to do with a transistor tester, but we didn’t have one. So we did what we always do these days…build it.

This useful little gizmo is based off a CMOS binary counter/divider which sweeps the collector with a steadily rising voltage over a few different base currents. There are two ranges for small signal and power transistors. And of course, a switch for NPN and PNP. In a shop like ours, we don’t usually need a piece of equipment like this, but having a curve tracer for the one or two times a year we actually need it makes it all worth while.

P.S. The curve seen on our custom red slip mat is a scope trace from a PNP we had lying around the shop; likely a 2N3906.