# transistor oc139 equivalent ?



## AurEL. (Sep 27, 2022)

Hi guys, I'm new here and I'm a big noob.

I have some issues finding some transistor, specially the oc139 and I need it for my project of pre amp... 

Can someone know if there is an equivalent ? or can I use an other transistor ? 

Thx you so much


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## HamishR (Sep 27, 2022)

It seems that the OC139 is an NPN Germanium transistor. Almost any NPN Ge transistor could be used. Generally you want low leakage and reasonable HFE. Google "OC139 datasheet" to find out typical HFE and find an NPN Ge transistor in that range. If you buy a few and put a socket on the board for the transistor you can try a few to see/hear which one sounds best. If you're looking for inexpensive NPN Ge transistors then Russian MP38s can give excellent results.


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## Cybercow (Sep 27, 2022)

The OC139 is an NPN germanium BJT.  Some equivalents are: OC140, CV7112, NTE103A, 2SK3835, 2N229, ASY29, AC187, and/or AC176.

Pretty sure there are several others as well. Depending on the specific build, a germanium BJT may not be necessary.


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## AurEL. (Sep 27, 2022)

Cybercow said:


> The OC139 is an NPN germanium BJT.  Some equivalents are: OC140, CV7112, NTE103A, 2SK3835, 2N229, ASY29, AC187, and/or AC176.
> 
> Pretty sure there are several others as well. Depending on the specific build, a germanium BJT may not be necessary.



Hi, thx so much   

They are hard to find  

I have those in stock right know : 
2N5088 (to92) - 2N2222A - 2N2907A - 2N3904 - 2N3906 - 2N5551 - 2N5401 - S8050 - S8550 - A1015 C1815 - A42 - A92 - A733 - C945 - S9014 - BC327B - BC337B - BC547B - BC557B​
Do you think any of this can do the job ? 
Thx you so much for your time, it's literaly my first pedal and I dont understand a lot of this for now.


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## Cybercow (Sep 27, 2022)

To best target the BJT for the job, it's kinda important to have a clue of what you're building. Have you looked at & compared the different datasheets for those BJTs?


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## AurEL. (Sep 27, 2022)

yeah I do, but I still have some issues 

for exemple :

- the original :            OC139 = 20V - 0.25A - 143 mW 
- the closest I have :  S8050 = 25V - 0.5A - 200 mW 

They both are Germanium BJTs NPN, but I dont know if it's close enough ? 

Thx you so much ! 😩


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## Cybercow (Sep 27, 2022)

AurEL. said:


> yeah I do, but I still have some issues
> 
> for exemple :
> 
> ...


Those should be fine. As small-signal Ge BJTs go, those specs are not a primary concern. Hfe and Leakage are the important factors.

What are you building with the Ge transistors?


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## fig (Sep 27, 2022)

S8050 is a silicon transistor. 👍


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## AurEL. (Sep 27, 2022)

Cybercow said:


> Those should be fine. As small-signal Ge BJTs go, those specs are not a primary concern. Hfe and Leakage are the important factors.
> 
> What are you building with the Ge transistors?


I'm trying to built a pre amp pedal > https://www.pedalpcb.com/product/pcb346/ 
It's the simpliste circuit I found


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## AurEL. (Sep 27, 2022)

fig said:


> S8050 is a silicon transistor. 👍


hum.... sorry to ask ( probably a stupide question ), but what is the difference ? 
Does it mean it can't be used instead of a Germanium ?


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## fig (Sep 27, 2022)

I think the 2N2222A you have will work fine for the Aft.


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## AurEL. (Sep 27, 2022)

fig said:


> I think the 2N2222A you have will work fine for the Aft.


You guys on this forum are the best, thx you so much  🤩


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## fig (Sep 27, 2022)

AurEL. said:


> hum.... sorry to ask ( probably a stupide question ), but what is the difference ?
> Does it mean it can't be used instead of a Germanium ?


The germanium or silicon is the electrode material used. Most germanium transistors are out of production.


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## AurEL. (Sep 27, 2022)

fig said:


> The germanium or silicon is the electrode material used. Most germanium transistors are out of production.


Yeah, I watch everywhere and I didn't find ( except very few, but very very expensive )   
So, if I understand well, those silicone transistor can be the job insted of the Germanium ?


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## fig (Sep 27, 2022)

Here is the pinout…


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## AurEL. (Sep 27, 2022)

fig said:


> Here is the pinout…


thx


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## fig (Sep 27, 2022)

AurEL. said:


> Yeah, I watch everywhere and I didn't find ( except very few, but very very expensive )
> So, if I understand well, those silicone transistor can be the job insted of the Germanium ?


It will in this and other cases, but not all. Some look for a voltage leak through the germanium.


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## AurEL. (Sep 27, 2022)

fig said:


> It will in this and other cases, but not all. Some look for a voltage leak through the germanium.


ok, I understand, thx 
I will try with my 2N2222A 🤞


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## Cybercow (Sep 27, 2022)

AurEL. said:


> hum.... sorry to ask ( probably a stupide question ), but what is the difference ?
> Does it mean it can't be used instead of a Germanium ?


Another point of interest regarding Ge BJTs is that most of them are VERY temperature sensitive. The OCxx and Cvxxxx series are more stable than others, but still subject to changes in ambient temperature. Silicon transistors are far more stable and do NOT exhibit a measurable "leakage" - which also fluctuates with temperature changes.

Just use a socket for the BJT and you can try a few different NPN trannies out. You might want to socket R3 as well. Often, when swapping out different BJTs, the biasing resistor value may need adjusting. And as fig points out, the 2N22222 should work just fine. Still I'd socket the BJT and R3 to try different things. When you find a good working combo of BJT and R3 value, you can solder them in place.

Cheers!


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## HamishR (Sep 27, 2022)

We guitar players are a bit weird because we seem to like old, crappy technology which is inefficient and obsolete. We love tube amplifiers because those old inefficient tubes sound good with a guitar. We love germanium transistors because they work so well with a guitar in an old, basic fuzz pedal. It's the way they interact with the guitar which we like. But it is 60-year old technology now and you have alternatives. 

As Cybercow says, germanium is very temperature sensitive, meaning that your favourite Ge Fuzz Face may make unusable sounds if used on a hot stage, as in an outdoor gig in summer, for example. Silicon transistors are generally a lot more stable. But silicon can sound brighter and not interact with your guitars controls as well.

The other thing about germanium transistors is that they tend to be low powered, ie their amplification levels are low. So when looking for a silicon replacement the first thing you want to look for (after whether it's NPN or PNP) is the HFE range. The HFE is kind of a power rating, and a lot of Ge transistors are under or around the 100 HFE mark, which is low by today's standards. That's why a 2N2222A might be a good choice, because it's usually around or below 200. A 2N3903 is another candidate - it's often even lower than a 2N2222A.


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## andare (Sep 28, 2022)

@AurEL. you should pick up this cheap component tester called TC1, available pretty much everywhere.





 It reads resistors, capacitors, diodes and transistors and it tells you if they are PNP or NPN, it shows you the pinout and it measures hFE and, for Germanium transistors, Iceo (the leakage).

Most Germaniums are PNP, most Silicons are NPN so choose the appropriate type for your build as per the docs.


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## Feral Feline (Sep 28, 2022)

I had to re-read that Transistor Substitution Chart... I thought it read:

"Be careful of fakes on eBay, Mouser.com, Digi-key.com, SmallBear and several other electronic parts vendors..."

Fake Ge trans on Mouser, Digi-key and Small Bear? 🙀

😹

A simple paragraph break or a reconstructed sentence with the legit vendors would prevent mistaking that period after eBay for a comma...


"...Be careful of fakes on eBay. 
Mouser.com, Digi-key.com, SmallBear and several other electronic parts vendors..."


Great chart though, looks like an update (much needed) of this ol' chestnut:


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## Cybercow (Sep 28, 2022)

Feral Feline said:


> Great chart though, looks like an update (much needed) of this ol' chestnut:
> 
> View attachment 33057



Like this one . . . .  ?


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## Feral Feline (Sep 28, 2022)

Cybercow said:


> Like this one . . . .  ?
> 
> View attachment 33058


😸 Yeah, that's the one, the same one you posted earlier in the thread.

Reading it again, it still looks like "...beware of fakes from eBay*,* Mouser.com, Digi-Key.com, SmallBear ...".


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## Cybercow (Sep 28, 2022)

Feral Feline said:


> 😸 Yeah, that's the one, the same one you posted earlier in the thread.
> 
> Reading it again, it still looks like "...beware of fakes from eBay*,* Mouser.com, Digi-Key.com, SmallBear ...".


Good point and catch. Thanks! I corrected them to reduce the confusion.


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## Feral Feline (Sep 28, 2022)

Thanks for those @Cybercow! Didn't realise that was of your own making!

I've been using the old one for years, so if that's yours as well I can't thank you enough for both the old and the new!


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## Cybercow (Sep 29, 2022)

Feral Feline said:


> Thanks for those @Cybercow! Didn't realise that was of your own making!
> 
> I've been using the old one for years, so if that's yours as well I can't thank you enough for both the old and the new!


Oh, no, no, no . . . .  I mean thanks, but I am not the creator of that chart. Like you, I found the old one years ago. A few years a go I updated it and started to re-propagate it across the groups and forums. The proximity of the words "_fakes from eBay. Mouser.com, Digi-Key.com . . . _" was an oversight on my part.


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## Feral Feline (Sep 30, 2022)

Good on ya for updating it!

Many thanks!


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## Andyisdumb (Oct 17, 2022)

Cybercow said:


> Another point of interest regarding Ge BJTs is that most of them are VERY temperature sensitive. The OCxx and Cvxxxx series are more stable than others, but still subject to changes in ambient temperature. Silicon transistors are far more stable and do NOT exhibit a measurable "leakage" - which also fluctuates with temperature changes.
> 
> Just use a socket for the BJT and you can try a few different NPN trannies out. You might want to socket R3 as well. Often, when swapping out different BJTs, the biasing resistor value may need adjusting. And as fig points out, the 2N22222 should work just fine. Still I'd socket the BJT and R3 to try different things. When you find a good working combo of BJT and R3 value, you can solder them in place.
> 
> Cheers!


Unrelated question, but why on the PCB are there four holes for the transistor? What is my simple newbie brain missing?


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## DAJE (Oct 17, 2022)

Andyisdumb said:


> Unrelated question, but why on the PCB are there four holes for the transistor? What is my simple newbie brain missing?


Different transistors have different pinouts. Meaning, you have to make sure which leg is which before you plug it in. Plugging a transistor in the wrong way will not work and could possibly damage the transistor.

EDIT: There are different holes to accommodate different configurations. Just use the one that lines up with what you have and ignore the 4th hole.


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