Ge Leakage in FuzzFace

[RedHouse]

I used the test fixture (jig) from RG's white paper "Technology of the Fuzz Face" to test 28 germanium NOS (AC128 and AC125) I bought recently.

With that jig only 3 out of 28 were under 500uA leakage but they only had gain of 35,45,65 well below range for fuzzface.

The thing is, lots of them were in the right gain range (70-130) for FuzzFace but had between 500 and 1,500 uA leakage, and the white paper indicates 500uA considered "bad" so there-in lies my question...

Q: Specifically, what effect does the leakage have on the sound? is it just a matter of eating up current (bad battery life) or does the leakage cause crappy sound, or hiss, or what?

[petemoore]

The Answer to your questions are yes.
 Maybe no.
 For complete details, interview a bunch of Germanuims in various FF settings. Trimpot Q2 collector, sokket the caps and transistor interviewing positions for EZ testing.
 Mixing with bipolars may yield various results, just watch your NPNs and PNPs.

[R.G.]

High leakage indicates either sloppy junction diffusion, or more likely, surface contamination. Surface leakage causes hiss and noise. Junction leakage is usually quieter, but with a tendency to drift badly.

I'd say that since you already have the parts, build something up and see how you like it. Put in sockets and see if the sound is OK, then fix problems.

Here's a little known tip: If you match the c-b leakage of two devices, you can use one as a normal transistor, and the other with the emitter open, connected collector to the base of the "normal" one and base to ground.

If the leakages are similar, the diode connected one shunts about as much leakage out of the base of the active one as leaks in from the collector. The active transistor then behaves more like it's normal.

Ideally, you have a good gain device with a leakage matched to a bad gain device; use the good gain device as the normal transistor, the bad one as the leakage-sucker. And be very careful in measuring leakage, putting devices in the test socket with pliers or tweezers or something. Your hand heat is enough to throw the leakage test off to the high side.

[saros141]

And be very careful in measuring leakage, putting devices in the test socket with pliers or tweezers or something. Your hand heat is enough to throw the leakage test off to the high side.

I second that. Even if you don't touch the body of the transistor, the heat will travel up the leads.  I just got done testing a couple hundred germaniums using R.G.'s neat system, and I found that if i picked up the transistor by its leads only and got it in the socket as quickly as possible (a few seconds), it still took at least 2 minutes for the reading to stabilize, in the leakage-testing mode.  Then I'd flip the switch to test gain, and after that stabilized and I recorded the reading, flip it back and notice the leakage reading is slightly higher, just from the heat of the flowing electricity I presume.

[petemoore]

The Tycho was oscillating, by only Waving my hand over the Ge transistor [cold where I was waving at the time] I could get a rise in oscillation frequency, touching it made it rises even faster of course, holding it made it go right past the top of my hearing range and misbias to the point of shutting off input signal...Too Funny !!

[Fret Wire]

First time I measured a Ge tranny, I had to move from the kitchen table, because the forced air heating/cooling duct was near the table. They're that heat sensitive.

[saros141]

The Tycho was oscillating, by only Waving my hand over the Ge transistor [cold where I was waving at the time] I could get a rise in oscillation frequency, touching it made it rises even faster of course, holding it made it go right past the top of my hearing range and misbias to the point of shutting off input signal...Too Funny !!

Wow, sounds like you could make a "Thermamin"  :lol: , if you could get it to cool fast enough...

[RedHouse]

High leakage indicates either sloppy junction diffusion, or more likely, surface contamination. Surface leakage causes hiss and noise. Junction leakage is usually quieter, but with a tendency to drift badly.

Thanks for responding RG, and that little tester jig really works well, thanks for that too (and all the other stuff you've shared over the years while I'm at it).

So it is a noise thing then, I'll need to plug 'em in and audition them as you said.