What's All This Stuff About Germanium Diode Leakage?

[SillyOctpuss]

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]

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.

 

[JetFixxxer]

Could you use the CONDUCTANCE function on a DMM?

 

[Chuck D. Bones]

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.

 

[JetFixxxer]

I have a Fluke 189 that I can measure Conductance, but never used it and let alone when to use it.

 

[SillyOctpuss]

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 Marks	Is (μA)	Rd0 (KΩ)	Comments
1n34a	Blk-Blk	5.84	8.9	Tayda
1n34a	Blk-Blk	8.00	6.5	Tayda
D9B	Red-Red	3.85	13.5
D9B	Red-Red	4.11	12.7
D9K	White-white	1.82	28.57
D9K	white-white	3.02	17.2
D9E	Blue-red	4.4	11.82
D9E	Blue-red	3.16	16.5
1n60	red	12.6	4.17	NOS Hitachi some are clear where the band had faded
1n60	red	14.1	3.69	Same as above
1n34a	blk	4.85	10.72	TFK
1n34a	blk	10.11	5.14	TFK
1n34a 1n34a	green Green	1.99 1.42	26.67 36.62

 

[jubal81]

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]

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]

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.

 

[SillyOctpuss]

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]

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]

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.

 

[sgtrutters]

I'm a little late to this game, but building a couple of Cornish G-2 clones. I've measured some germanium diodes with the current method and they measured 19.2mV, after doing the calculations I come up with about 267 (ex: 19.5/100 52/.195 = 266.6667) Am I correct in reading this as 267K ohms of resistance, so not good for use in BMP style circuit? FV on these tests right about 0.33v so they would be good in that sense. When it comes to testing these things for leakage, along with transistors, I get confused.

 

[Chuck D. Bones]

Your calculations are correct. That leakage is pretty low for a Ge diode. You can try them in a G-2 and see if you get enough sustain. I'd like to know which diodes Cornish puts in the G-2's he builds.

 

[Chuck D. Bones]

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.

1N5227B is a 3.6V zener diode. Since they are installed back-to-back like normal clipping diodes, then they will never see the 3.6V reverse voltage. Zeners tend to have a larger Vf than a standard small-signal Si diode like a 1N4148. They are less leaky than most Ge diodes, but considerably more leaky than a 1N4148.

 

[jessenator]

First you need a 1/2-way decent DMM. It has to have a 200mV range (or something like that) and it has to have 10M input resistance.

Hook everything up like this:
Plug a 100K resistor into your breadboard. Connect +9V to one end. Plug in the diode you want to test with the cathode connected to the other end of the 100K resistor. Connect the ground side of the 9V supply to the anode of the diode. Connect your DMM +lead to the +9V end of the 100K resistor. Connect the DMM -lead to the diode end of the 100K resistor. Set the DMM to read millivolts.

Make sense so far?

When the DMM reading stops changing, write down the number. If it's 83mV, write it down as 83. Divide the number you wrote down by 100. That's the leakage in μA. In this example, it would be 0.83μA. Now divide 52 by that number to get the resistance in KΩ. That's 52 / 0.83 = 62.65KΩ.

Sorry for the necro, but I wanted to make sure I understood this before I started. This is my setup (with some DMM lead stand-ins). Is this correct?

 

[Chuck D. Bones]

Yes.
Make sure you know which end of the diode under test is the cathode. Normally, the band is at the cathode end. Many (most?) Russian diodes have the color band(s) at the anode end. They do this to be assholes.

 

[jessenator]

Never mind… not a dumb question, dumb equipment. Moved to the fluke

 

[Chuck D. Bones]

Only the final number matters. When we hook up the diode to the test jig, we transfer an unknown amount of heat to the diode from our fingers. That heat need to dissipate in order for the leakage current to settle.

 

[jessenator]

It's stable now I've switched DMMs

I keep my workspace pretty stable temps and don't handle directly with my hands.

My D9Ds I've done so far are leaky, but mostly in the same range 1.6–1.8

The ITT 1N34As I've got vary quite a bit: 0.3 micro amps to around 5

And these "1N270" s can't be real as they sit around 30nA as a 1N60P registers 0.22 micro; BAT41 at 0.12 micro