Attention Pedal Builders and DIY Pedal dudes: How do you test Germanium Transistors?

[tejastubes]

I am interested to know how you guys test you Germanium Transistors, what equipment you use, and what measurements/readings you look for when selecting a transistors. Also, if you would like to post the transistors you have found to be the best sounding, please do so.

[SonicVI]

This is probably the most popular testing device.
http://www.peakelec.co.uk/acatalog/jz_dca55.html

[drbob1]

Umm, you're not going to find "best sounding" transistors because they're so darn inconsistent. You need to check the gain and the leakage...

[tejastubes]

Originally Posted by drbob1

Umm, you're not going to find "best sounding" transistors because they're so darn inconsistent. You need to check the gain and the leakage...

readings for gain and leakage etc?

[mmolteratx]

Originally Posted by SonicVI

This is probably the most popular testing device.
http://www.peakelec.co.uk/acatalog/jz_dca55.html

Ya, love my DCA and LCR meter from Peak. Really high quality and very easy to use.

Best sounding is tricky. British types (NKT, OC, etc) tend to have higher junction capacitances than most others and are as a result "warmer".

I've got a big list of stuff that I've measured (around 200 for capacitances of varying types, measured several thousand for gain and leakage). I'll see if I can find it and post it. What you're looking for gain and leakage wise is totally dependent on the circuit.

[tibbon]

My tube tester can test transistors too

[capricorn_1]

Originally Posted by SonicVI

This is probably the most popular testing device.
http://www.peakelec.co.uk/acatalog/jz_dca55.html

yeah well worth getting one of these, couldn't do without one!

[spentron]

During a pause between tuning my Mellotrons.

(j/k)

[macki]

I would want to know the I-V curve for the diode. From that you can figure out the small and large signal characteristics of the diode. A slow way would be to put a resistor in series with the diode and hook it up to a variable voltage supply - measure the diode voltage and current for various supply voltages. Plot that up and you have the I-V curve - watch though as the current is exponentially related to the voltage. There is a temp dependance though but you will get a basic idea of the behavior of the device

For capacitance I would use the manufacturer's value. It will be variable depending on the current (if I remember correctly) but should not really change dramatically.

[Youngpedals]

Read this:

http://www.geofex.com/Article_Folders/ffselect.htm

[fr8_trane]

Originally Posted by tejastubes

I am interested to know how you guys test you Germanium Transistors, what equipment you use, and what measurements/readings you look for when selecting a transistors. Also, if you would like to post the transistors you have found to be the best sounding, please do so.

The idea and theory
http://www.geofex.com/Article_Folders/ffselect.htm

In practice
http://crawlsbackward.blogspot.com/2...stors-for.html

Here's another take:
The easiest way to do this, I believe, is to use a breadboard. You need a fresh 9v battery, a 2.2m resistor, and ideally a a 2.472k resistor... but I wouldn't drive yourself mad aiming for ideals (especially when dealing with germanium transistors). If you can get 2.47k that's good enough I think - I used a 2.2k and a 270r resistor in series to get 2.47k exact. You want to set things up on your breadboard along these lines (n.b. we are dealing with PNP transistors here - alter things to suit NPN if you need):




Bias calculator for getting consistently good Fuzz Faces after you've tested your trannies.
http://www.diystompboxes.com/biascalc/ffbias.html

Course the BEST way to avoid testing GE trannies at all is to use a low gain Si transistor as Q1 and put the Ge in Q2. This should pretty much eliminate the instability of a dual Ge FF due to leakage and heat sensitivity. Q1 sets the gain for Q2 apparently so as long as Q1 is stable so is Q2.

You could also go with an all Low gain si FF because they can be made to sound identical to Ge.
http://fuzzcentral.ssguitar.com/axisface.php

[cj_wattage]

Originally Posted by mmolteratx

Ya, love my DCA and LCR meter from Peak.

Me too! I have both, and they've paid for themselves several times already.

Originally Posted by mmolteratx

I've got a big list of stuff that I've measured (around 200 for capacitances of varying types,

Interesting. Do you use the LCR to measure capacitance at the junctions?

I find that the LCR can get "confused" in certain situations where there is capacitance and resistance or inductance present, and all are low value. I find myself sometimes wishing the LCR had a manual mode, even though I find the auto-ness of it quite appealing in the vast majority of cases.

[Bucksears]

Unless you have a batch of transistors already, or you want to go into business selling matched sets, have you considered buying them pre-matched from Smallbear Electronics?
He sells matched sets of germanium trannies for Fuzz Face-type and Tonebender-type fuzzes. That's where I get mine.

[dlab]

Originally Posted by fr8_trane

The idea and theory
http://www.geofex.com/Article_Folders/ffselect.htm

In practice
http://crawlsbackward.blogspot.com/2...stors-for.html

Here's another take:
The easiest way to do this, I believe, is to use a breadboard. You need a fresh 9v battery, a 2.2m resistor, and ideally a a 2.472k resistor... but I wouldn't drive yourself mad aiming for ideals (especially when dealing with germanium transistors). If you can get 2.47k that's good enough I think - I used a 2.2k and a 270r resistor in series to get 2.47k exact. You want to set things up on your breadboard along these lines (n.b. we are dealing with PNP transistors here - alter things to suit NPN if you need):




Bias calculator for getting consistently good Fuzz Faces after you've tested your trannies.
http://www.diystompboxes.com/biascalc/ffbias.html

Course the BEST way to avoid testing GE trannies at all is to use a low gain Si transistor as Q1 and put the Ge in Q2. This should pretty much eliminate the instability of a dual Ge FF due to leakage and heat sensitivity. Q1 sets the gain for Q2 apparently so as long as Q1 is stable so is Q2.

You could also go with an all Low gain si FF because they can be made to sound identical to Ge.
http://fuzzcentral.ssguitar.com/axisface.php

Do this if you can follow instructions and you don't want to blow $70 on an Atlas tester...