106NU70 Germanium Transistor Equivalent

greypilgrim76

greypilgrim76

Active member
Hi All,

I made the classic mistake of impulse buying a PCB a while back--in this case the Muffin Factory--and while I'm excited to take on such a complex build, I didn't check the components before pulling the trigger. Now I'm realizing that the 106NU70 germanium NPN transistors are pretty much unobtanium these days, and I'm sort of stuck on what to substitute for them. I've found some NPN germaniums in a few places like Small Bear, but I'm not sure what hits the reuquired sweet spot of 55-65 hfe. I don't have a transistor tester, so I'd prefer to buy something that will likely fit that range, if possible. Or, maybe a place that sells them with verified hfe ranges. Any suggestions on where to find this last piece of the puzzle?

Many thanks!
 
Sovcom on ebay seems to be the place to buy germaniums. My order is supposed to show up soon and I ordered from them because other people mentioned it in some threads on here. They aren't measured so buy extra so you can test them, and since you gotta buy extra it's worth importing anyway cuz they are so much cheaper.
I ordered mp38a's to use but have not used/tested them yet since I'm still waiting. Hopefully someone will be in here suggesting some specific ones they have used for you soon
 
It’s not FF or TB where people usually aim for certain gain and leak. IMO everything between 20-90 hfe is mostly fine. Also the feedback circuit from C to B helps clipping stages transistor biasing. And if not, fine tune E or C resistor values.
 
So as I was poking around online, I came across these at Small Bear:

smallbear-electronics.mybigcommerce.com

2N1302 Germanium Transistor NPN RCA

New England's source for guitar pedals, pedal parts and electronics.
smallbear-electronics.mybigcommerce.com smallbear-electronics.mybigcommerce.com

If I got one in the 51-60 Hfe range and another in the 61-70 range, would these be reasonable substitutes? The internet tells me their leakage is usually passable for this sort of circuit. I don't know enough to know what I don't know, though... :)
 
NU70 is listed as 35-70 beta.
the biggest thing you are after is low leakage. From there, adjust E and C resistors as @JohnnyCreepy said, until you are somewhere around 4.5v, give or take a half volt. See kit rae schematics for notes on these resistors.
Edit:
Disregard the comment on base voltage.
According to GGG, Q2 and Q3 should be around:
Q2
Collector 3.8
Base 0.6
Emitter 0.03

Q3 (Q4 in muffin factory)
Collector 3.8
Base 0.6
Emitter 0.03
(Leakage will alter these some, as will E and C resistor changes)

Leakages are listed on the schematic in the build doc as
Q2: 260uA and Q4: 390uA
Most Russian germs will be able to attain that. If you have lower leakage transistors, that's fine. But I would keep it below 500uA, for sure.
A lower beta and lower leakage would be fine as well. Something like a 35-45 hfe and <50uA.
As always, mind/check the pinout. Paint/dot on collector with EBC PINOUT for NU70s. A lot of Russians are CBE I believe.2n130x are EBC.
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