2N2189 Transistors

[PerroGrande]

I recently found some 2N2189 metal-can transistors.  The build date shows 8204, and I rather suspect that they've been untouched since...  After a bit of searching on Google and the like, I keep getting linked to the same "data sheet".  It is nothing more than a list of part numbers and a few values for each transistor on the list.  It shows the 2N2189 as a Germanium PNP transistor.  I've been able to verify that they are, in fact, Germanium PNP transistors (YAY!!!) but don't know much more about them than that. 

The 1-line "spec sheet" indicated Hfe of around 80, which was about what I got in several tests on the actual units.   Just for kicks, I whipped together a fuzzface using two of them, and it worked -- although it sounded like it could use some tweaking to get the biasing right. 

Does anyone have recollection of or a real data sheet on these things? 

[Dragonfly]

http://www.americanmicrosemi.com/information/spec/?ss_pn=2N2189

[PerroGrande]

Thanks, Dragonfly!

I think their max Hfe of 180 is probably a bit ambitious -- the handful that I tested were on the lower side of the chart.  However, the other ratings make them look decent for the applications that I would use them for.   I'm going to mess with them a bit more this weekend and see if I can get a good feel for how they like to be biased.

[Dragonfly]

Thanks, Dragonfly!

I think their max Hfe of 180 is probably a bit ambitious -- the handful that I tested were on the lower side of the chart.  However, the other ratings make them look decent for the applications that I would use them for.   I'm going to mess with them a bit more this weekend and see if I can get a good feel for how they like to be biased.

No problem.

That website has quite a bit of data on obsolete transistors that I havent been able to find elsewhere.

Definitely report back on how those work out for you !

AC

[PerroGrande]

I didn't end up with much spare time this weekend, but I did manage a few uninterrupted hours this morning to play with my collection of 2N2189's.

Expectedly, the leakage measurements were all over the board, but all that I tested fell within a reasonably usable range.  Likewise Hfe varied noticeably on the group that I tested -- anywhere from about 45 up to about 120.  Most fell into the 70-90 range, at least within the batch that I tested.  Neither result is unexpected.

To do some "ear-based testing" I wired up a classic positive-ground fuzz-face on a breadboard.  The results were not particularly inspiring -- a very muted tone with extremely mild distortion in most positions of the "drive" pot (on the emitter of Q2), with some really obnoxious fuzz at the extreme setting of the drive pot. 

Not good, but also not unexpected.  I used nothing but stock values, so the chances of successful biasing were rather remote. 

Sure enough, when I took a look at the collector voltage of Q2, I knew that what my ears told me was happening was, in fact, happening.  With the stock value of 8.2K from the fuzzface circuit, the collector voltage of Q2 was around -1 volt.  While I know the operating voltage of Q2 is a widely debated subject, I wanted to get this thing biased around the supply midpoint (-4.5v) just to see how it would sound with a more reasonable bias.

To accomplish this, I replaced the 8.2K resistor with a 10K trim pot and cranked away until -4.5 was achieved.  For future reference, with all other values at the original settings (330 Ohm for the "other" Q2 collector resistor), around 5K produced -4.5v on the collector of Q2. 

With more proper bias voltages (surprise, surprise) the 2n2189 fuzzface really came to life.  Q1's collector was about 0.5 volts higher than I might have expected from the original (sitting right around -1.0 volts quiescent).  I haven't looked into additional tweaking to drop this voltage a little closer to the original, so I don't have any comments on the sonic implications that this might produce.

Overall, the unit clearly had that "germanium sound" -- at least to my ear.  Arguably (subjective comment to follow!), the 2n2189 sounded a little brighter to my ear.  Perhaps the parasitic capacitance characteristics of this tranny are a bit better than the AC128's (it wouldn't take much!).  I suspect it's ability to produce the entire audio range is better than the original, which might explain the brightness comment.  I may try a few pF of capacitance between Base and Collector of Q1 and Q2 to "de-edge" the sound just a notch.  Again, all personal preference.

So -- in summary -- I'm going to call it successful.  Some additional tweaking will be in order to get the sound where my ear wants it, but I'm certainly going to build-out one of these things in a real box to have in my collection.

[Dragonfly]

Cool report !

I have zillions of germaniums that I need to do similar tests on. Finding time these days is tough though.

Still, it goes to show that with germaniums, provided you get them with a reasonable leakage amount, within a good hfe range, and you bias them properly, you can make a good sounding fuzz.