3AX31C Germanium gain

Addendum: I also picked up some of the so-called "AC128s" from China.

These are interesting. Not so much in their usability: that seems unlikely. Best I've found out of the bunch this far has been a leakage of 570uA.

But, they're *really* shiny. Like, gleaming. Almost makes me wonder if somebody is trying to do new production.

If they are, they're either failing miserably, or shipping all the qc rejects to the states.
 
andare said:
I use a TC1 tester and it has served me well. The RG Keen method works better if you rig it up but I decided it wasn't worth it for all the junk parts I buy :)
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The TC1 is a fantastic tester and not just because of the $20 price tag. I find myself using the TC1 way more often than my DCA75. It’s just quicker and I’ve not had any issues with accuracy over the past few years of using them. I’ve probably purchased four of them -still less than one DCA75.
 
Stickman393 said:
Addendum: I also picked up some of the so-called "AC128s" from China.

These are interesting. Not so much in their usability: that seems unlikely. Best I've found out of the bunch this far has been a leakage of 570uA.

But, they're *really* shiny. Like, gleaming. Almost makes me wonder if somebody is trying to do new production.

If they are, they're either failing miserably, or shipping all the qc rejects to the states.
Click to expand...
And Poland
 
Tc-1 is a good investment.

But it's not good for testing germaniums.

They don't quite get the leakage values right past 100uA, and are absolutely worthless at measuring anything that takes a while to stabilize.

Which is to say: certain Russian transistors it does quite well with. The ones that you can pop into an RG keen tester and immediately get reliable values from.

But... We're less concerned with what a transistor does at the first "on" instance. More concerned with what a transistor does when it's powered and has had time to stabilize. Cause that's what we're gonna be doing with our pedals.

Right now: this is how I'm rigging it up. This was quickly cobbled hacked together as a means to go through a metric fuckton of germs that I've been accumulating.

1000009572.jpg
 
Stickman393 said:
Addendum: I also picked up some of the so-called "AC128s" from China.

These are interesting. Not so much in their usability: that seems unlikely. Best I've found out of the bunch this far has been a leakage of 570uA.

But, they're *really* shiny. Like, gleaming. Almost makes me wonder if somebody is trying to do new production.

If they are, they're either failing miserably, or shipping all the qc rejects to the states.
Click to expand...
I would bet it's more likely they are polishing old germs in order to facilitate the relabeling process.
 
I mean, I knew they weren't actual AC128s!

Color me curious. And color me unwilling to take other people's word for it.

Also, color me out a few bucks with a bunch of useless germs. Nbd.

I kinda am hoarding all the germs right now.
 
Stickman393 said:
I mean, I knew they weren't actual AC128s!

Color me curious. And color me unwilling to take other people's word for it.

Also, color me out a few bucks with a bunch of useless germs. Nbd.

I kinda am hoarding all the germs right now.
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Wait til you see the mailbox thread tomorrow.
Also, we probably shouldn't bid each other up on eBay. 😂
 
Update, here's a re-test with the TC1.
This actually seems useful?

Having said that, they've just been sat at room temperature. Do they need to be used actively to stabilise?

1752621649219.jpeg
 
Some germs take longer than others to stabilize. The TC-1 generally does a quick test that doesn't really take this natural settling into account.

What that means, though, is that you can generally expect the leakage and gain values read by the tc-1 to be slightly higher than a stabilized example.

That one in particular looks decent. Use it! Try to bias it! See how it sounds.
 
Stickman393 said:
GT402b or E work quite well for a leakier, gainier transistor.

GT309b's are very high gain and very low leakage.
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Question for you. When might I want leakier transistors? Just took receipt of this haul and will test them before buying other Germs, but I guess might look into a small batch of GT402s.

I'm mostly interested in preamp designs for both guitar, microphone, and live level. But everyone should build a classic fuzz at some point right?

1752622761957.jpeg
 
Q1 and Q3 in a tonebender need some leakage. All depends on the design, some folks engineered a degree of leakiness to their advantage
 
rossbalch said:
Question for you. When might I want leakier transistors? Just took receipt of this haul and will test them before buying other Germs, but I guess might look into a small batch of GT402s.

I'm mostly interested in preamp designs for both guitar, microphone, and live level. But everyone should build a classic fuzz at some point right?

View attachment 99000
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I'm a mere buffoon, a soldermonkey, but here's what I know about leaky transistors:

Q1 and Q3 in a Tone Bender MKI, as @Stickman393 said, or it won't work at all/sound bad. This circuit is supposed to be gated.
Q2 in a Tone Bender MK1.5 so Q2c is at about 8V, otherwise it will just be a dark Fuzz Face. This is supposed to be a bright, ratty Fuzz Face.
Q3 in a Tone Bender MKII (same reason as the 1.5) and a Tone Bender MKIII (no idea if leakage is necessary here).


If you use leaky transistors in a Ge Fuzzrite, it will be gated (no single coil noise) and awesome, but remember that gating = no cleanup with the volume knob.
 
Hmm so I've been testing the NPN versions the 3BX31C, and the TC1 doesn't detect the Iceo leakage on them, I'm not sure if that means the leakage is just very low, or if because it's NPN it doesn't think they are Germanium? Anyone got experience testing NPN Germs with a TC1?
 
These are the results of my tests so far. All done on the TC1

edit: updated table

1752726711324.png

ND means not detected / reported.

Unfortunately I have no way to know if ND means the leakage is too low to detect or is crazy high.
 
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rossbalch said:
These are the results of my tests so far. All done on the TC1

edit: updated table

View attachment 99072

ND means not detected / reported.

Unfortunately I have no way to know if ND means the leakage is too low to detect or is crazy high.
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My TC1 fails to read some transistors, sometimes it thinks they are diodes, sometimes resistors or caps :)
But generally I don't worry because they're probably bad units. What can you do with an hFE of 13 anyway?

But all those with gain between 60 and 90 I would just pop into a Rangemaster and see if they do anything. Use tweezers to handle them.
 
andare said:
My TC1 fails to read some transistors, sometimes it thinks they are diodes, sometimes resistors or caps :)
But generally I don't worry because they're probably bad units. What can you do with an hFE of 13 anyway?

But all those with gain between 60 and 90 I would just pop into a Rangemaster and see if they do anything. Use tweezers to handle them.
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I guess it would be nice if the NPNs were low leakage cause NPN germs are so rare. Guess I'll have to construct the RG Keen tester after all.
 
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