Germanium guidance

[jwyles90]

Hey all,
So I’ve decided to try my hand at a build that uses germanium transistors (I ordered the Deimos PCB from Aion FX) and am realizing I’m pretty clueless when it comes to what exactly I should be looking for when sourcing these guys. I know that right now is probably the worst time to try to find any, but im hoping to get some guidance around what to look for.

I’ve attached the build docs, which include the measurements for the three transistors. I saw there are some available on stomp box parts in the 50-90 range (2nd attachment). Would those work, or am I better off looking elsewhere?

 

[jeffwhitfield]

I think for Q1 an Q2 they might work just fine. It's the Q3 one that needs to be a higher hFE for the whole thing to really work. I built a Maestro Fuzz Tone FZ-1 clone a week ago and used some AC128's I had laying around. Not much off from what a Tone Bender requires really. I acquired most of my Germaniums by hunting down various sets on eBay and other sites off the beaten path. Did get some from StompBoxParts...but you have to jump on them when they're listed else they get sold out really fast...especially the higher hFE ones!

Honestly, your best bet would be to find a place that can sell you a set that has been tested and has the right hFE and leakage values you need to make it really work well for you. JoeDocMusic appears to have some sets. You can also find sets on Reverb a lot of times.

Another option, and one that I've used myself, is to find some on PedalHacker.com and use his testing service to get transistors that match the specs you're looking for. Unfortunately, many of the ones he has are Russian transistors which have a tendency to have pretty low leakage and might not work so well for a Tone Bender, which does need some leakage.

I'd say give JoeDocMusic a shot. Short of buying a buttload of transistors and testing them yourself, that might be your best bet.

 

[jeffwhitfield]

Another option is DIY-Tubes.com. I've purchased a number of transistors from them, mainly silicon ones though. But I'm sure the GE ones are good too. My Drunk Beaver TBII pedal was built using MP20B and P416B transistors. Might be able to pull some of those together on that site.

 

[jwyles90]

I think for Q1 an Q2 they might work just fine. It's the Q3 one that needs to be a higher hFE for the whole thing to really work. I built a Maestro Fuzz Tone FZ-1 clone a week ago and used some AC128's I had laying around. Not much off from what a Tone Bender requires really. I acquired most of my Germaniums by hunting down various sets on eBay and other sites off the beaten path. Did get some from StompBoxParts...but you have to jump on them when they're listed else they get sold out really fast...especially the higher hFE ones!

Honestly, your best bet would be to find a place that can sell you a set that has been tested and has the right hFE and leakage values you need to make it really work well for you. JoeDocMusic appears to have some sets. You can also find sets on Reverb a lot of times.

Another option, and one that I've used myself, is to find some on PedalHacker.com and use his testing service to get transistors that match the specs you're looking for. Unfortunately, many of the ones he has are Russian transistors which have a tendency to have pretty low leakage and might not work so well for a Tone Bender, which does need some leakage.

I'd say give JoeDocMusic a shot. Short of buying a buttload of transistors and testing them yourself, that might be your best bet.

Awesome, thanks for all the help! I just ordered a set from JoeDoc, I’ve seen his site mentioned on here a few times before, so that seems like a solid option. Plus $5 shipping is hard to beat haha. Stoked to see how these turn out!

 

[jeffwhitfield]

Awesome, thanks for all the help! I just ordered a set from JoeDoc, I’ve seen his site mentioned on here a few times before, so that seems like a solid option. Plus $5 shipping is hard to beat haha. Stoked to see how these turn out!

Definitely let us know how they turn out.

I hunted down a batch of Russian trannies which suit my needs. I might build a Tone Bender at some point just for kicks.

 

[Big Monk]

If you plan on tweaking the classic circuit, the transistor leakage and hFE is pretty inconsequential in the MK II.

It matters if you plan on using the vintage circuit values but in this day and age, why do that?

If you tweak the bias resistors on all 3 transistors and make sure to use a low leakage unit in Q2, you really can’t mess it up with pretty much any transistor between 70-110 hFE.

 

[jwyles90]

If you plan on tweaking the classic circuit, the transistor leakage and hFE is pretty inconsequential in the MK II.

It matters if you plan on using the vintage circuit values but in this day and age, why do that?

If you tweak the bias resistors on all 3 transistors and make sure to use a low leakage unit in Q2, you really can’t mess it up with pretty much any transistor between 70-110 hFE.

That’s a good point. I noticed they include trim pots in the build doc so I figured you’d be able to tweak them to make it work regardless. This is my first time both using germanium in a pedal and even playing a pedal that uses it
All of this is making me realize I know basically nothing about what germanium does or how it functions in a pedal. Do you have any tips or resources for getting a better understanding of that?

 

[Big Monk]

That’s a good point. I noticed they include trim pots in the build doc so I figured you’d be able to tweak them to make it work regardless. This is my first time both using germanium in a pedal and even playing a pedal that uses it
All of this is making me realize I know basically nothing about what germanium does or how it functions in a pedal. Do you have any tips or resources for getting a better understanding of that?

I would say keep it simple. Germanium transistors do 2 major things that set them apart from their Silicon brethren:

1.) They have leakage and that cause them to have temperature based instability, i.e. temperature induced voltage fluctuations

2.) They have a softer, more rounded transistion into distortion. This plays a part in their ability to exhibit touch sensitivity, etc.

There are basically 2 major ways to attack vintage circuits that use Germanium transistors:

1.) Tune the transistors to the circuit, i.e. use the vintage schematic and circuit values and audition transistors until it sounds good. This is where leakage really matters as you don’t have any other levers to pull to adjust. This is the old school way because prime devices that dropped right into vintage circuits use to be plentiful.

2.) Tune the circuot to the transistors, i.e. pick the transistors and tweak the circuit around them. This effectively nullifies the need for any specific leakage values and is more flexible today as prime devices with vintage specs are dwindling.

 

[fig]

I would say keep it simple. Germanium transistors do 2 major things that set them apart from their Silicon brethren:

1.) They have leakage and that cause them to have temperature based instability, i.e. temperature induced voltage fluctuations

2.) They have a softer, more rounded transistion into distortion. This plays a part in their ability to exhibit touch sensitivity, etc.

There are basically 2 major ways to attack vintage circuits that use Germanium transistors:

1.) Tune the transistors to the circuit, i.e. use the vintage schematic and circuit values and audition transistors until it sounds good. This is where leakage really matters as you don’t have any other levers to pull to adjust. This is the old school way because prime devices that dropped right into vintage circuits use to be plentiful.

2.) Tune the circuot to the transistors, i.e. pick the transistors and tweak the circuit around them. This effectively nullifies the need for any specific leakage values and is more flexible today as prime devices with vintage specs are dwindling.

#3 - They are badass.

 

[jwyles90]

2.) Tune the circuot to the transistors, i.e. pick the transistors and tweak the circuit around them. This effectively nullifies the need for any specific leakage values and is more flexible today as prime devices with vintage specs are dwindling.

That sounds like the path of least resistance, given how challenging it seems they can be to get a supply of. So for that route I'm assuming that's done either through a trimpot or adjusting resistor values?

 

[Big Monk]

That sounds like the path of least resistance, given how challenging it seems they can be to get a supply of. So for that route I'm assuming that's done either through a trimpot or adjusting resistor values?

Yup. Fixed resistors or trim pots.

Well, you need at least 15 microamps leakage in Q1 for that stage to forward bias. I target anywhere between 7.8-8.2 vDC on Q1. I’ve found in my studies that lower values here help the MK II to cleanup better.

I would select a low leakage unit for Q2. You don’t need to play around too much with collector voltage here but keep in mind Q2 can have a big effect on Q3.

Q3 can be low to medium leakage and I like values between 7.6-8.2 vDC. Lower voltages on the collector of Q3 make the pedal fatter, have more sustain but also more noise. Gating on Q3 was a design element in the originals to keep noise down.