# transistors



## swetonic (Dec 12, 2020)

I'm building the tone vendor. And I don't have the germanium transistors. I'd like to educate myself a little bit on transistors. If I wanted to find a replacement for the OC81D, how should I go about doing that? Google seems to help of course, but I was also wondering if a circuit calls for an NPN, or PNP transistor, does that mean you can't use a BJT transistor?

And if anyone has a suggestion for a replacement, that's appreciated.

Thanks


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## HamishR (Dec 12, 2020)

With germanium transistors you can usually substitute another type easily enough. NPN stands for "negative-positive-negative", so I think you can guess what PNP means.     Generally it's easier to use NPN Ge transistors in a negative ground circuit. But there are some notable exceptions. A lot of popular Ge transistors are PNP so using them in a Fuzz Face will mean having to use a negative power supply which in turn makes things trickier if you want to daisy-chain power on a pedal board.

The pins on a Ge transistor are CBE - collector, base, emitter, same as in a BJT silicon transistor. So you can often use a BJT transistor in place of a Ge transistor but they will sound quite different and a silicon transistor will not have any leakage which may make them not work in some circuits. I have subbed low-gain Si trannies for Ge in a few circuits with good results but you do have to adjust things sometimes. Si can be brighter than Ge so you may need to add a cap to roll off high end, for example.

So if you want to find a Ge substitute for an OC81D just google "OC81D substitute" which will suggest an AC125. Or, once you have established that it's a PNP transistor you can try any number of PNP Russian transistors. Buy a transistor tester - they're not expensive - to establish how much leakage the transistor has and its power rating.


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## ManicStrat2112 (Dec 13, 2020)

Just to add...…..it's kind of a general rule that good germanium npn transistors are harder to come bye. In my experience the npn's have a lot higher leakage (a lot have unusable high leakage) and are generally way noisier. As for PnP on the other hand, they are easier to find, have less leakage, and are usually quieter. 
Also, I wouldn't get hung up on the OC81D transistor. You can get the Tonebender circuit to sound really good with just about any germanium transistors if they're in the right spec. The Tonebender mki and mkii are my all time favorite fuzz circuits, so I've built quite a few of them, and some of the best sounding ones I've made had Russian pnp's in them.
A good place to start is Smallbear Electric. He's got matched sets for Tonebenders that sound great.


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## Chuck D. Bones (Dec 14, 2020)

swetonic said:


> I'm building the tone vendor. And I don't have the germanium transistors. I'd like to educate myself a little bit on transistors. If I wanted to find a replacement for the OC81D, how should I go about doing that? Google seems to help of course, but I was also wondering if a circuit calls for an NPN, or PNP transistor, does that mean you can't use a BJT transistor?
> 
> And if anyone has a suggestion for a replacement, that's appreciated.
> 
> Thanks



NPN and PNP _are _BJTs.

Since you're new here, how about an introduction?  What are your electronics capabilities?  Do you own a DMM or transistor tester?  Do you know how measure voltages in-circuit?  

Building with Germanium transistors is always a challenge and is not recommended for your first build (if this is indeed your first build).  If you answered "no" to either of the last two questions, then you should consider building an easier pedal.  

As the other guys said, you can sub various Ge transistors, they just need to PNP.  Use sockets, good ones made for transistors because you're going to be swapping them around.  Q1 is leakage-biased, which means we need it to be leaky to work.  Get your transistors from a reputable supplier like Small Bear.  Tell them you're building a Tone Bender mark 2 and they should be able to hook you up with the right parts.  Otherwise, plan on buying more than three transistors because they may not all work right in this circuit.  Don't buy Ge transistors on eBay unless you know how to test them because many (most?) of them are not good.


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## swetonic (Jan 12, 2021)

Hi - sorry I never replied to you. I've built 5 pedals so far. I do own a DMM, but not a transistor tester. I ended up finishing the tone vendor, and it works. I used *2N404 *transistors, with sockets. The sound is pretty good, but I don't hear attack pot changing the sound. Haven't figured that part out.


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## manfesto (Jan 13, 2021)

HamishR said:


> The pins on a Ge transistor are CBE - collector, base, emitter, same as in a BJT silicon transistor.


This isn’t always true, off the top of my head I know the GT308 has a BCE pinout

If it’s not a transistor you’re familiar with, it’s always a good idea to try and find the datasheet and confirm the pinout


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## Chuck D. Bones (Jan 13, 2021)

Indeed, or use a reliable transistor.


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## Coda (Jan 14, 2021)

swetonic said:


> ... I don't hear attack pot changing the sound.


I wouldn’t worry too much about that. That’s the nature of the MK II...


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