transistor oc139 equivalent ?
- Thread starter AurEL.
- Start date
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.
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.
Cybercow
Well-known member
Those should be fine. As small-signal Ge BJTs go, those specs are not a primary concern. Hfe and Leakage are the important factors.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 !
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
fig
Village Idiot
The germanium or silicon is the electrode material used. Most germanium transistors are out of production.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 ?
fig
Village Idiot
It will in this and other cases, but not all. Some look for a voltage leak through the germanium.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 ?
Cybercow
Well-known member
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.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 ?
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!
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.
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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