Help with understanding transistor leakage

JamieJ

JamieJ

Well-known member
Hey guys and gals,

Inspired @thewintersoldier fuzz series it has finally prompted me to search through a stash of Ge for my tone bender MKI build. I’m a bit confused about leakage reading on my tester (cheap multifunction TC1).
25F261B3-2A48-43DE-A26A-B2FEEC0A9EAF.jpeg
Sorry I can’t rotate the picture.

So is this OC71s leakage 170ua from the ICEO or do I need to calculate 170/65+1?

Or is there something else I am missing?

I am really confused and after a lot of reading online, I can’t find a coherent answer.

Thanks!
 
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JamieJ said:
Hey guys and gals,

Inspired @thewintersoldier fuzz series it has finally prompted me to search through a stash of Ge for my tone bender MKI build. I’m a bit confused about leakage reading on my tester (cheap multifunction TC1).
View attachment 13045
Sorry I can’t rotate the picture.

So is this OC71s leakage 170ua from the ICEO or do I need to calculate 170/65+1?

Or is there something else I am missing?

I am really confused and after a lot of reading online, I can’t find a coherent answer.

Thanks!
Click to expand...
I’ve got the exact same tester and I use it quite often. Although mostly to check resistor, capacitor values because it’s quick and easy to use as well as accurate for those two applications.

I recently purchased a DCA 75 and have compared the reading from it next to the TC1 and often the results are different for transistors, diodes etc. It’s strange as in some cases it matches up fine, but in most it doesn’t.

Long story short, the TC1 is a great tester for resistors and capacitors although I wouldn’t exactly trust it for transistors and diodes. The DCA 55 or 75 will definitely be more accurate in that regard. Or you could use your DMM and the RG Keen method.

Also, I hate that the photos I post are always rotated 90 degrees when posting on this forum. Not many others seem to have the issue but it seems you and I do :)
 
Kroars said:
I’ve got the exact same tester and I use it quite often. Although mostly to check resistor, capacitor values because it’s quick and easy to use as well as accurate for those two applications.

I recently purchased a DCA 75 and have compared the reading from it next to the TC1 and often the results are different for transistors, diodes etc. It’s strange as in some cases it matches up fine, but in most it doesn’t.

Long story short, the TC1 is a great tester for resistors and capacitors although I wouldn’t exactly trust it for transistors and diodes. The DCA 55 or 75 will definitely be more accurate in that regard. Or you could use your DMM and the RG Keen method.

Also, I hate that the photos I post are always rotated 90 degrees when posting on this forum. Not many others seem to have the issue but it seems you and I do :)
Click to expand...
Thanks. I was planning on using it to roughly sort my batch then test them in sockets in the pedal. I need to invest in a DCA 55/75 at some point.

I have all the parts to build RG Keens tester so I need to build that to work from as my next step.

Thanks @Kroars
 
From what I understand, there are firmware upgrades to those $20 component testers available that make them more useful for things like leakage readings. You might want to try looking into that before dropping $100 on a Peak (though I highly recommend dropping $100 on a Peak!).

As long as your meter is giving you *consistent* readings then you can easily sort through your stash and organize into a couple of piles like "lower gain, higher leakage" "higher gain lower leakage" etc. That should be more than enough data to build a cool fuzz.

Honestly, you shouldn't stress out too much about getting the "right" values for a tone bender build. If you have a pile of Ge on hand, just build the circuit and swap transistors until the pedal sounds cool to you. Two transistors that read identically on a meter can sound completely different in the circuit. And it's not like any of us have enough vintage tone benders* sitting around to make a case for what a mki should "actually" sound like either.



* (and also a time machine to take us back to a time whenthe components were still in spec)
 
mdc said:
From what I understand, there are firmware upgrades to those $20 component testers available that make them more useful for things like leakage readings. You might want to try looking into that before dropping $100 on a Peak (though I highly recommend dropping $100 on a Peak!).

As long as your meter is giving you *consistent* readings then you can easily sort through your stash and organize into a couple of piles like "lower gain, higher leakage" "higher gain lower leakage" etc. That should be more than enough data to build a cool fuzz.

Honestly, you shouldn't stress out too much about getting the "right" values for a tone bender build. If you have a pile of Ge on hand, just build the circuit and swap transistors until the pedal sounds cool to you. Two transistors that read identically on a meter can sound completely different in the circuit. And it's not like any of us have enough vintage tone benders* sitting around to make a case for what a mki should "actually" sound like either.



* (and also a time machine to take us back to a time whenthe components were still in spec)
Click to expand...
+1. Numbers are useful, and all, but sometimes an ear is better. Who here would love to play a vintage MK 1? Everyone. But if you have everyone a vintage MK1, most of them would sound different. Sure, the internal numbers would match up, but that doesn’t guarantee you a good tone…
 
This thread has been super helpful, thanks everyone. I have finally gotten around to building @music6000 s "Dizzy Elk" and close to being able to test out transistors and this (along with lots of other threads I've read) has been helpful in finding a starting place to understanding how important leakage is.

I gotta take the kiddo to swim lessons, I'm probably about an hours worth of work away from having it ready to test out. I'm stoked to learn and share what happens.
 
Well I'm trying to do the same thing and am getting some weird results. I'm trying to test 3 x asx12d, 1 x ASX12C and 1 x oc71. I'm using the circuit described in the article listed above and if I try to measure the leakage across the 2.4k resistor I'll get say 0.158 which will start to decrease immediately like its a cap which is draining. Then whennI measure the voltage at the 2.2m resistor I'm basically seeing the full 9volts.v I'm really confused now. It should be a very simple process which I must be screwing up somewhere
 

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