Germanium transistors - what do I do?

[SillyOctpuss]

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.

 

[Cucurbitam0schata]

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.

 

[SillyOctpuss]

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.

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.

 

[benny_profane]

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

 

[Chuck D. Bones]

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...

 

[SillyOctpuss]

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.

 

[Chuck D. Bones]

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

 

[fig]

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

 

[SillyOctpuss]

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.

 

[SillyOctpuss]

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?

 

[SillyOctpuss]

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.

 

[SillyOctpuss]

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?

 

[Big Monk]

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.

 

[Mcknib]

ICEO is the leakage current afaik

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

 

[Chuck D. Bones]

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.

 

[SillyOctpuss]

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?

 

[Mcknib]

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 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

 

[Chuck D. Bones]

Indeed. Don't get hung up on HFE.

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

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

 

[Guava13]

Slap that OC71 in a Rangemaster!

 

[caiofilipini]

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!