What's All This Stuff About Germanium Diode Leakage?

SillyOctpuss

Well-known member
Ok it looks like my multi meter is borked. The figures I'm getting are very weird. I've been wanting a new one for a while so I'll have a hunt to see what's suitable. As an example I have some figures below.

My PSU is supplying 9.16v to my breadboard and everything is connected as you advised.

TFK 1n34a starts at 792mv and stabilises at 754mv. 754/100=7.54 52/7.54=6.9
My dmm only picks up a reading in the 4M (0.13) and 40M (0.099) ranges.

The other two diodes I tested - 1n60 and d9b had equally weird results.

My old DMM was excellent until it died. This one does not appear to have been a suitable replacement.
 

Chuck D. Bones

Circuit Wizard
It may seem weird, but when measuring the resistance of a diode it is perfectly normal for a DMM to only give resistance readings on certain ranges and those reading will not exactly agree. A DMM's resistance function is designed to measure resistors, which are linear devices. Try to measure a non-linear device like a diode or transistor and the DMM gets confused.

My Fluke 115 does the same thing.
 

Chuck D. Bones

Circuit Wizard
Maybe, I don't have a DMM with that function so I can't try it. In principle, it should work. As with resistance, you will need to set the ranging to manual.
 

SillyOctpuss

Well-known member
Found some time to do this properly and measured two of each type I had. I let them all sit until they stabilised fully this time.
Part No.Identifying MarksIs
(μA)
Rd0
(KΩ)
Comments
1n34aBlk-Blk5.848.9Tayda
1n34aBlk-Blk8.006.5Tayda
D9BRed-Red3.8513.5
D9BRed-Red4.1112.7
D9KWhite-white1.8228.57
D9Kwhite-white3.0217.2
D9EBlue-red4.411.82
D9EBlue-red3.1616.5
1n60red12.64.17NOS Hitachi some are clear where the band had faded
1n60red14.13.69Same as above
1n34ablk4.8510.72TFK
1n34ablk10.115.14TFK
1n34a
1n34a
green
Green
1.99
1.42
26.67
36.62
 

jubal81

Well-known member
Got some measurements from one of my 1N695As.

Chuck method:
.74uA leakage and 70.2K

Resistance on my Fluke 83V: 2.5M
Leakage as measured by cheap 328 component tester: .44uA
 

Chuck D. Bones

Circuit Wizard
I can explain the differences

My method applies close to 9V and measures leakage current. The resistance calculated is the diode's impedance for a diode voltage of zero volts.

The Fluke applies probably 100nA on that range and measures the voltage drop. The indicated resistance is what you'd have if the diode was a real resistor, which it's not.

The 328 tester probably applies it's full internal regulated voltage (+5V) and measures leakage current.

All methods are valid and provide a means of sorting diodes for leakage and resistance. I believe that my method is the best predictor of how the diode will behave when connected back-to-back as a soft clipper.
 

SillyOctpuss

Well-known member
Got some measurements from one of my 1N695As.

Chuck method:
.74uA leakage and 70.2K

Resistance on my Fluke 83V: 2.5M
Leakage as measured by cheap 328 component tester: .44uA
I had a similar experience between results from Chuck's method and my component tester and multi meter. That's why I assumed I must be doing something wrong because of the large disparity between resistance results in the two methods.
 
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SillyOctpuss

Well-known member
I can explain the differences

My method applies close to 9V and measures leakage current. The resistance calculated is the diode's impedance for a diode voltage of zero volts.

The Fluke applies probably 100nA on that range and measures the voltage drop. The indicated resistance is what you'd have if the diode was a real resistor, which it's not.

The 328 tester probably applies it's full internal regulated voltage (+5V) and measures leakage current.

All methods are valid and provide a means of sorting diodes for leakage and resistance. I believe that my method is the best predictor of how the diode will behave when connected back-to-back as a soft clipper.
Thanks for the explanation
 

jubal81

Well-known member
Being that these low-leakers are like finding hens' teeth, I've got a substitute for you guys if you're up for soldering a SOT23 SMD part. The BAT54s is two anti-parallel diodes and they have the same exact leakage as the 1N695. Put a 68R resistor in series with those, and I can barely tell any difference between that and a real 1N695 - seriously.
I've done this little breakout board and shared it on OSHpark for you guys. Just two parts: the BAT54s and a common 68ohm TH resistor. The "S" matters if you order it from somewhere other than through the Mouser link I added. Gotta be BAT54S.

Here's a link to order the little breakout PCB. This is BOTH diodes, so you only need two of these for a G2 or Nugget. Just load up this breakout, add some leads, and solder it into ONE diode spot of a pair.
 

Mir9

Member
The Muffs I've built with germanium diodes are the Pharaoh, Fuzz War v2, and the NG-2 so I'm hoping to have all this information "click" for me.

Add the 1n5227b to the test pile, as that's what they replaced the germanium diodes with in the Fuzz War some years back. I read about it some time ago, but had it confirmed recently when DeadendFX traced the Super Fuzz War as their "Skirmish" project.
 
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