3AX31C Germanium gain

Ok so I made the RG Keen tester, I think based on the continuity test, when the switch is in the up position, the bottom two poles are connected? And in the down position, the top two poles are connected? I wired it so the 2m2 is connected to the top lug, and the middle lug is connected to the ground plane.

I used this guide. https://www.freestompboxes.org/viewtopic.php?t=9851 EDIT, the power and DMM meter connections are reversed compared to the guide due to NPN topology of the 3BX31C.

If I got everything right, one of the 3BX31C that showed up with no leakage reading on the TC-1 had a reading of:

2M2 floating 0.083v, and 2M2 connected 0.772v.

Which would mean 0.772 - 0.083v = 68.9 hFE, and ~ 30uA leakage?

1753004065439.jpeg 1753004111502.jpeg
 
Last edited:
I tested one of the PNPs (3AX31C) that I had tested on the TCR-1.

The TCR-1 tested a hFE of 64 and an Iceo of 66uA.

My Keen tester (assuming it worked) read a voltage of 0.075v with 2M2 floating and 0.566v with 2M2 connected to ground which would equate to a hFE of 49.1 and a leakage of <50uA. Which I think means the tester is working?
 
Hey folks. I built my first ever bread board circuit, an LPB-1 and tested the NPN 3BX31C. It biased up nicely, here's the oscope results,

1000khz 0.6v P-P signal input
1753951121267.jpeg

1000khz 1.2v P-P signal input
1753951150829.jpeg

Haven't measured the biasing resistor values yet, but seems like the low leakage readings were real. Pretty nifty lot given out of the 10 I got from AliExpress 6 of them have a Hfe over 65. No idea how it sounds yet.
 
You must log in or register to reply here.
Back
Top