I have some questionable Ge diodes, so I thought I would test to see if they were truly Ge or not.  Using the tips from Barry’s video on diode testing I proceeded to go about checking the forward voltages using my Peak Atlas DCA55, just like in the video.  However, I came up with some head scratching results.

First of all, my DCA55 registers voltages out to 3 digits compared to Barry’s in the video that registers voltages out to 2 digits, so obviously I probably have a later version of the DCA55.  Testing a diode labeled 1N34, which may have come from BYOC or Mammoth, I get a forward voltage of slightly >0.8 volts which appears to put it in a likely Si diode territory.  Testing with a couple of other different regular multimeters, the forward voltage measures slightly >0.4V, which are consistent with each other and more typical of a Ge diode.  Maybe the DCA55 is doubling the forward voltage measurement somehow?  I do notice that the test current on the DCA55 varies between ~4.1mA to 4.3mA and is not consistent from one measurement to the next.  Reference known Ge diodes from Small Bear measure around 0.3V using both the DCA55 and the other two multimeters, which is puzzling compared to the supposed 1N34 measurements relative to the different devices.

Using the DCA55 and warming up (between fingers for ~25 sec.) the known Ge reference diode for a short period of time does produce a drop of 0.010V to 0.015V, but the same is true for the 1N34 and also a Si diode.  Using the other multimeters, the Ge reference diode and the 1n34 have ~0.020V drops in forward voltage, and the Si registers a 0.005 drop so there is a ~0.015V difference between the Ge and Si diodes.  I also chilled the diodes with a cold pack and came up with similar results, except there was an increase in forward voltage.  The increase was not that different when measuring with the DCA55, but was pretty significant with the other multimeters increasing ~0.050V for the Ge diodes and <0.005V for the Si diodes.

My conclusion is that for determining Si vs. Ge, the DCA55 is not helpful.  Using my other multimeters, it does appear that I can distinguish between Ge and Si diodes.  It also seems that chilling the diodes makes it easier since the voltage change is greater than using the heat method for the Ge diodes and negligible for the Si diodes.

I appear to have confirmed that the 1N34 labeled diode is indeed Ge.  Other diodes I have purchased as 1N34’s test as silicon and close inspection with strong magnification reveals these are 1n4733 diodes.  These were obtained from Mammoth and probably a reason why they are out of business.  I never checked these after I bought them about 4-5 years ago and should have.  Other diodes I have are also mislabeled.  A pair of 1n914’s from BYOC and a sealed package of 1N914’s from Radio Shack are revealed to be 1N4148’s under magnification, although apparently 1N914’s and 1N4148’s are nearly identical.

If anyone has an idea why the DCA55 has trouble evaluating the diodes would be greatly appreciated.  I just know I cannot reproduce Barry’s results; however, it appears that my other multimeters work fine for diode evaluation.