Germanium Voodoo Transistors

[Gledison]

hey,
I've just learned how to measure the  real hfe of germanium trannies. not much difficult that.
I've tested AC125 and AC128s. it might be that I was veryyy much screwwwed! almost all of them showed a leakage of at least 1, 0 V, correspondint to 410uA in my circuit.
R.G Keen said that more that 300uA of leakage is not acceptable..
im measuring in a couple of them a high Hfe, but also a high leakage. so , what is the most important?
o assume, high gain, little leakeage, sure, but having a final and considerable hfe of 60-70 or 120-150 is enough?
this is a voodooland! I've started last month building and now im spending hours measuring the bloody transistors just to be sure I will get a nice fuzz
any light???
cheers

[croquet hoop]

Actually, what matters most in a fuzz is the ratio, rather than absolute values. You could get a killer sounding fuzz with Q1 at 50 hfe and Q2 at 70. You don't really need high gain. However, it's best to keep leakage under a certain value, as you've noticed.


(now I understand your comment about voodoo on the other Ge thread )

[Gledison]

eheheh, there are voodoos everywhere!!
so, you also agree that a leakage of max 300 uA is the limit?
im very pssed off because I bought from a guy that supposedly checked them for real gain..
and I might have been screwed!!
cheers

[croquet hoop]

From R.G. Keen's article :

How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.

So 300 is more than ideal, but at 400uA they may not be unusable. Build your fuzz with these transistors first, and if you really can't get anything good sounding, buy some from Smallbear or banzai (I think both of them test hfe and leakage) with better characteristics. But there's no reason to throw them to the bin yet.

[GermanCdn]

Banzai does test for leakage, but they charge twice as much for that.  My experience with their germs has been pretty good, I'd sooner order twice as many germs and weed them out than pay for the rated ones, but I am also allergic to fuzz pedals for the most part .

[Gledison]

The ACs125 I've got are measuring around 1mA to 1.5 mA, exactly, miliAmper!
Some of you guys have experience with so high leakage? or somehow my measurement is garbage...
btw, Im measuring using a breadboard and measuring the Voltage using the 2,2M resistor and 2x 1K resistor in series with a 470R.
maybe is time just to build a Bloody Fuzz and see how it sounds....Ah, btw, someone has a link of a video or post showing how  a "perfect" Fuzz should sound like? most of the sounds I like are mixed with diff pedals, so difficult to judge!
thanks!

[midwayfair]

The ACs125 I've got are measuring around 1mA to 1.5 mA, exactly, miliAmper!
Some of you guys have experience with so high leakage? or somehow my measurement is garbage...
btw, Im measuring using a breadboard and measuring the Voltage using the 2,2M resistor and 2x 1K resistor in series with a 470R.
maybe is time just to build a Bloody Fuzz and see how it sounds....Ah, btw, someone has a link of a video or post showing how  a "perfect" Fuzz should sound like? most of the sounds I like are mixed with diff pedals, so difficult to judge!
thanks!

AC125 ... or any other AC12x ... are notoriously leaky. Just a horrible, horrible series of transistors to begin with that's been picked over to death by mojo fuzz transistor seekers. I would wager that the chances of finding a good one are so remote that it's never, ever, ever worth it to purchase them except when tested by some other sucker who bought in bulk.

The ones you have anen't worthless, but they're likely to be noisy as crap and/or act like low gain in a fuzz face. Just don't solder them into the board in case you don't like what you hear. You can definitely use them in Q3 in a Tone Bender or Q1 in a Harmonic Percolator. There are other fuzzes that rely on leakage to serve as part of the biasing.

Your gain ranges are fine, though. One of my favorite fuzz faces has 40hfe in Q1 and 60hfe in Q2 and it's loud as balls. It's the ratio, not the gain range.

[chromesphere]

Hey Jon,
Just wanted to comment on this thread.
Don't get me wrong, I agree with you, but to a certain extent.  I have bought many ac transistors and they have been hit and miss.  Some are HUGELY leaky.  I bought some ac176's that were so leaky they had thermal run away.  Hotter, more leakage, hotter, more leakage.  Until the evitable.
I don't know where you got your ac125;s from Gledison, but I can tell you, all the ac125's I have bought have been quite good.  Leakage less then 400ua (usually between 100-300ua).  Good gain ranges.  I've also had people that have bought these from me and measured against my readings using more then one method and confirmed this, good gain ranges and good to acceptable leakages. So to say that ALL AC's are garbage is a little final and not in line with my experience at all.  
Depends where you source them I guess.  You may have gotten a 'skimmed' lot.  The left overs that the seller didn't want.  It happens unfortunately.
There are also bins that these are sorted into.  That's what the V and VI and IV numbers are.  Gain bins. and generally as the leakage of these are around 10%-20% of the collect current (from my personal experience) as the collector current goes up, so does the leakage.  So if you buy a lot from a high gain bin, up goes the leakage!  But personally I think if you are getting 1ma of leakage you have gotten duds.  I have never seen an ac125 measure this high for leakage before.  either that or you measuring them incorrectly
EDIT: not to mention there are a number of manufacturers that made the AC125 during its production run.  I've only tested the more 'modern' version.
that's my opinion YMMV.
Cheers,
Paul

[chromesphere]

Just read through the whole thread.  Yep I agree.  gains aren't everything.  You can get a bit of extra sustain if you have the right gains of course, but that's not going to help you if you the transistor has a harsh frequency response.  Unfortunately germanium transistor set retailers have educated everyone into placing importance on gain and leakage alone.  If you don't have the EXACT specs -> throw them in the bin which of course is not true. Frequency response is just as important and can vary widely from one transistor to the next. That's one of the reasons I like the ac128/125.  They are a good all rounder.

Anyway, I'm not an expert in these matters. Its really just a accumulation of what I have experienced, thus far.
Paul

[culturejam]

I agree with Chromey.

Germanium trannies are all over the place. And you can't judge them on gain or leakage alone. When dealing with old tech, it's half art / half math.

[pedalman]

I even made a nice tester, but after a few rounds I put my tail between my legs and just ordered from smallbear. To many factors. I tell him the sound I want and he nails it every time. Only 24 hours in a day and most of them go to work and pedals. No need to waste any on transistors (not to mention headache)

[chromesphere]

Factors.  hah.  I think the funniest thing about this whole measuring germaniums thing is when people buy a load of a transistor that says something like 70-120 hfe on the datasheet.  "they don't measure 70-120!".  What are the test conditions of the lab?  ambient temperature for example?  is your air-condition on?  leakage doubles with an increase in 10 degrees.  Its kind of like trying to hit a moving target.  Hence why electronics industry switched to silicon I guess.  You don't have any temperature instability issues like you have with germanium.
Seriously though, if you have you some lying around, just throw them into a circuit and see what they sound like.  Don't even measure them.  I've done this 'blind test' before and sometimes I'm surprised at the results!  its not always critical (unless the hfe's and leakages are WAY off).
Paul

[pedalman]

Mini camp fires and A/C's in our enclosures !
I remember a buddy of mine playing like crap and blamed it on the equipment not being warmed up

[chromesphere]

cold transistors might misbias your tonebender but warming them up wont help you if cant play guitar lol
Paul

[ch1naski]

cold transistors might misbias your tonebender but warming them up wont help you if cant play guitar lol
Paul

that's where I keep hitting a brick wall: no talent.

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