Where to find really low gain NPN Silicon Transistors

[bushidov]

Hi All,

Typically, in the rare instance I need something like this, I go to SmallBear. They have NOS of 2N334A NPN Silicon Transistors with Hfe's in the single digits up to the 20s and 30s. When pairing them with somewhat leaky low gain PNP Germanium Transistors in Sziklai Pairs, or a low-gain and low leaky NPN Germanium Transistors in Darlington Pairs, they rock, because I can still get a full "gain" of in the couple of hundreds of Hfe.

But these are long out of print. So where can I get really low NPN Silicon Transistors from that will work in fuzz pedals? I know the 2N3903, the little brother of the 2N3904, isn't too bad. Using R.G. Keen's 4uA base method, I measured them at around a little over 100 of gain.
https://www.digikey.com/products/en?keywords=2N3903%20PBFREE

I also tried on DigiKey a 2N2369A. It was even lower, in the high 60's. For a 2020 Silicon NPN Transistor, that's about as low as I've found them.
https://www.digikey.com/product-detail/en/central-semiconductor-corp/2N2369A-PBFREE/1514-2N2369APBFREE-ND/4806847

Any other places that still make these kind of things? Is there a way to "fake" a transistor into acting like a lower gain transistor?

Sorry for sounding like an amateur, but as you can guess, I am a bit of one.

[willienillie]

I bought a bag of these D33D30s a couple years ago, and they have averaged around 90~100 for gain.  They make a good Si fuzz face.  Not the cheapest option, but they look cool.

https://www.allelectronics.com/item/d33d30/npn-si.-transistor-t0-92hs/1.html

[digi2t]

2N2219 tend to be pretty low gain. They are the low gain version of the 2N2222.

MPSA42 are usually under 100.

MPS3704 is another.

BD139 is an Axis Fuzz favorite.

I tend to find that high voltage (Vceo, Vcbo over 50v) transistors tend to have lower published gains.

[Fancy Lime]

Don't try to find low gain transistors, roll your own! It's called piggybacking and can work really well in my experience, although not everybody seems to like it. The basic principle can be seen here:
https://www.diystompboxes.com/smfforum/index.php?topic=116158.msg1074490#msg1074490
Have a look at the individual and combined hfe values. If you use a smaller resistor between Q1 and Q2, and Q3 and Q4, the hfe goes down even further. Basically, you are using Q1 (or Q3) as a diode to degrade the performance of Q2 (or Q4). This works best when the diodes are a close match to the transistors internal BE diode, hence the use of transistors in the Q1 and Q3 position instead of using other diodes. Sounds fantastic in various 60's Fuzz circuits imo. If you make the resistor between the paired transistors a pot, you have an adjustable hfe (kind of). I have used this as a gain control in LPB and Orpheum Fuzz type circuits in the past and really liked it.

Cheers,
Andy

[bushidov]

Don't try to find low gain transistors, roll your own!

I've heard about Piggybacking Transistors a while ago from an R.G. Keen post. I haven't tried it yet, but I read that with a trim pot between both transistors emitter pins and a small 47pF-100pF cap, its supposed to sound like a Germanium Transistor.


I'll admit, I am a bit skeptic of the Germanium claim, but I just bread-boarded this up and indeed, the gain does seem to vary with the trim pot and I can get it quite low with a pair of matched 2N3904 transistors. I still need to try it in a pedal, but now you've peaked my interest.

Does it really sound like a Germanium transistor, though? That seems like a rather bold claim.

[digi2t]

I've used piggybacking in an NPN silicon Buzzaround-a-like. In my best hippy poetry, it will not cop the feel of germanium, but will kinda sorta mimic the performance. Somewhat. Worked fine for me, and sounded pretty darned good.

But, as Fancy points out, it is a good way of taking medium gain transistors and dropping the gain.

I forgot to add the 2N2218 to the list. Even lower gain than the 2N2219.

[amptramp]

Operating power transistors at low current will take them into a low-gain region and will also drop the Vbe somewhat so they may be closer to germanium.  Many power transistors are low-gain devices anyway.  The TIP41 typically has an hfe of 100 at low current.

[slashandburn]

Well this thread is a revelation. Cheers!

[dennism]

I'll throw 2N4123 into the mix too.   Cheap, currently produced and readily available with hfe around 100-120, it's my favorite for silicon fuzz faces.   I know Tayda has them, but I haven't ordered any parts lately so I don't know how the pandemic is affecting their shipping times.