# Germanium transistors - what do I do?



## SillyOctpuss (Jun 22, 2021)

So I found 5 germanium transistors I didn't know I had last night.  I've got 3x ASX12D, 1 x ASX12C and 1 x OC71. The question is what the hell do I do with them? Can anyone give me a crash course in how to measure for gain and leakage? I'm assuming I'll need to do that before deciding what to try and build with them.


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## Cucurbitam0schata (Jun 22, 2021)

one route is to do a direct search - if you google the entire forum and shop, you will come up with posts and product pages that have those transistors.

for example: 

```
[site:pedalpcb.com oc71] shows a bunch of posts for the simulcast and duocast.
[site:pedalpcb.com ASX12D] looks like someone used an ASX12D for a sunflower.
[site:pedalpcb.com ASX12C] got nothing for ya there... ;)
```

old transistors are always tricky, because it's best to measure each one for leakage (hFE). i tried a few for a percolator that were the "right" part numbers, but sounded really off. tucked a few other randos in that were in the ideal range, and they were way better.


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## SillyOctpuss (Jun 22, 2021)

Cucurbitam0schata said:


> one route is to do a direct search - if you google the entire forum and shop, you will come up with posts and product pages that have those transistors.
> 
> for example:
> 
> ...


Thanks.  I'm going to sit this weekend and measure the gain and leakage then go from there.  I've found a pretty decent video showing the process.  Shouldn't take long as I only have 5 to get through.  I'm fully expecting none of them to be usable but we'll see.


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## benny_profane (Jun 22, 2021)

This page from RG Keen has a good method for checking gain and leakage of Ge transistors:



			http://www.geofex.com/article_folders/ffselect.htm


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## Chuck D. Bones (Jun 22, 2021)

SillyOctpuss said:


> So I found 5 germanium transistors I didn't know I had last night.  I've got 3x ASX12D, 1 x ASX12C and 1 x OC71. The question is what the hell do I do with them?


I'd be happy to take them off of your hands...


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## SillyOctpuss (Jun 22, 2021)

That may actually happen.  I'll post my results and see if I can build anything I actually might want with them.  If not I'll offer them out to anyone who can use them once we see their gain and leakage.


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## Chuck D. Bones (Jun 22, 2021)

Unless they are completely dead, they can always be used for something.  Clipping diodes if nothing else...


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## fig (Jun 22, 2021)

I've got some that show a short between two legs, but remove one offending leg you've got a Ge diode.


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## SillyOctpuss (Jun 22, 2021)

Chuck D. Bones said:


> Unless they are completely dead, they can always be used for something.  Clipping diodes if nothing else...


That's a pretty good idea if I'm stuck.  I'll see what they look like when I get time to measure them.


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## SillyOctpuss (Jul 4, 2021)

I bought one of those cheap component testers from amazon and tested these last night.  These are the results if anyone knows what the hell this means.

ASX12D - 1   
hfe = 70
                      ube = 209mv
                      ic = 6.7ma
                      iceo = 22ua
                      ices = 1ua

ASX12D - 2    
hfe = 82
                       ube = 142mv
                       ic = 0.91ma
                       iceo = 60ua
                       ices = 2ua

ASX12D - 3     
hfe = 74
                       ube = 132mv
                        ic = 0.83ma
                        iceo = 61ua
                        ices = 5ua

ASX12C            
hfe = 68
                        ube = 212mv
                         ic = 6.7ma
                         iceo = 38ua
                         ices = 2ua

OC71               
 hfe = 70
                         ube = 112mv
                         ic = 1.3ma
                         iceo = 0.59m
                         ices = 37ua

So the only thing in that I actually know is hfe but have no idea on the other figures.  Can anyone help me out and let me know what's the best circuit to use try and use these in?


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## SillyOctpuss (Jul 4, 2021)

thewintersoldier said:


> Without knowing leakage it's hard to say. Safe bet would be a couple fuzz faces. Maybe a mk3 tonebender or buzzaround



I was hoping one of those figures WAS leakage.  I thought these component testers measured leakage.  That's why I bought it tbh.


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## SillyOctpuss (Jul 4, 2021)

I've just breadboarded the germanium tester from tagboard effects http://tagboardeffects.blogspot.com/2012/08/germanium-transistor-tester.html and the leakage figures I'm getting are pretty much lining up with the ICEO figures above.  Is that definitely not the leakage?


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## Big Monk (Jul 4, 2021)

SillyOctpuss said:


> I was hoping one of those figures WAS leakage.  I thought these component testers measured leakage.  That's why I bought it tbh.



Iceo is leakage. I have one of those component testers as well.


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## Mcknib (Jul 4, 2021)

ICEO is the leakage current afaik 

I being current between collector C and emitter E with the base open O


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## Chuck D. Bones (Jul 4, 2021)

You are correct, Sir!

Iceo and Ices are both leakage from collector to emitter.  Iceo is with the base lead open and Ices is with the base lead shorted to the emitter.  Iceo is the better indicator for leakage in a pedal circuit.  I would consider anything under 100μA low leakage and anything under 30μA very low leakage.  That OC71 is very leaky, but still usable in the right circuit, like a Tone Bender MK 1.

Make sure you wait for the transistor to cool off for a few minutes after you connected it to the tester.  A little heat from your fingers will throw the readings off.  You'll see Iceo continue to drop as the transistor cools down.

Ube = Vbe = base-emitter voltage at the indicated collector current.  These testers pick some arbitrary collector current and then measure Vbe & HFE at that current.  In most pedal circuits, Ge transistors are run at 1mA or lower.


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## SillyOctpuss (Jul 4, 2021)

Thanks gents.  Any suggestions from anyone on what they might try and build with these? My first thought was a fuzzface but the hfe is a bit low on them all isn't it?

Edit - to clarify the reading I've done recently on fuzzfaces I want Q2 to be 100-130hfe don't I?


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## Mcknib (Jul 4, 2021)

Thanks @Chuck D. Bones very informative as always.....I think!...just need a little time to absorb it

@SillyOctpuss I've used much lower 30 to 60 hFE Russian germaniums in fuzz faces no problem the bonamassa fuzz face uses low hFE Russian transistors 

I wouldn't say they're particularly low use your 68 for Q1 and 82 for Q2 it should be fine









						Dunlop JBF-3 Joe Bonamassa Fuzz Face
					

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 500 verified designs. DIY your own boutique effects!




					tagboardeffects.blogspot.com


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## Chuck D. Bones (Jul 4, 2021)

Indeed. Don't get hung up on HFE.  

To quote that great British philosopher R. Plant...

_"Lotsa people talkin', few of them know..."_


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## Guava13 (Jul 4, 2021)

Slap that OC71 in a Rangemaster!


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## caiofilipini (Jul 4, 2021)

That's very high leakage for a Rangemaster, but worth a try.

And I second what folks said about fuzz faces, my favorite sounding fuzz faces, including several I breadboarded and or built, were all low hFE Germanium transistors. MT current favorite, which I'm gonna put inside a Dunlop round enclosure, has hFE 60 and 72 in Q1 and Q2 respectively. It's a matter of taste, but those are definitely usable!


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## SillyOctpuss (Jul 5, 2021)

Thanks everyone.  I'll breadboard a fuzzface to try them out and go from there.  I'll report back after I've tried a few things


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## Chuck D. Bones (Jul 6, 2021)

Just received 56 of these (that was all the guy had).  Only sampled a few so far.  This one may be the hottest of the bunch...





Check the LDC!  Spring of 1969.  _Beck-Ola_ had just been released.


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## SillyOctpuss (Jul 7, 2021)

Wow.  What's the highest hfe you've ever seen on a germanium transistor @Chuck D. Bones ?


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## Chuck D. Bones (Jul 7, 2021)

That is pretty high.  I've measured a couple of 2N1308's approaching 300.  That part number is selected for high gain.  I bought a lot of 100, tested them all and at least half were over 150.


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## Chuck D. Bones (Jul 8, 2021)

Here's the hottest Ge trans I've measured, it's a 2N1309 from that same buy.  Had to run it on the curve tracer to verify.









At the center of the graph, the collector current lines are 3.5 minor divisions apart, or 700μA.  The base current steps are 2μA apart.  HFE = 700μA/2μA = 350.  The top two lines are a little over 900μA apart. HFE = 900μA/2μA = 450.  It's real.  I found 32 of 'em with HFE > 250.


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## cooder (Jul 8, 2021)

That is some hot stuff there, wonder how they sound! Also, as far as I can tell the cheapy 328 tester seems to agree with the more fancy curve tester then mostly, right? 
This is all pretty rivetting stuff, I got a bunch of Russian trannies that made it here after a 2 1/2 month odessey through the murky waters of international shipping and I still have a few more to come, fingers crossed...


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## Chuck D. Bones (Jul 8, 2021)

All of the Russian trannies I've bought measure HFE < 100, mostly around 60 - 70.  Which is fine.  I have no clue where to use a High-Gain Ge transistor, but I'll figure it out.


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