High-gain germanium transistor pedal circuit recommendation

[lmorse]

I have just acquired some high-gain germanium transistors, 200-350hfe. I have 6, and would like some recommendations for a noob circuit to build please.

[Thecomedian]

There's no additional info.

What part numbers are they? Do a web search for those part numbers with "(transistor#) datasheet" and pore over those. You might find out that the recommended bias condition to get the most hFE out of them is 10mA or 50uA or anywhere inbetween. Take a look at the datasheet for 2n2222, and you will notice that there are both low and very high gain values for the transistor due to it's own preference for 'optimal' Ic for given voltages.

ex: http://www.onsemi.com/pub_link/Collateral/2N5088-D.PDF  gain is 300 min for microamps and 5V, and gain is 350 min for milliamps and 5V.

Say they wanted a 10mA current, for instance, but you stuck em in a Fuzz. Now that hFE might only be something on the order of 100 instead of 200-350.

If we knew the part numbers some people might have better suggestions, but I think it's worthwhile to explore the datasheets and figure out how a specific transistor functions, and that can eventually lead to an intuitive understanding of what a transistor (for given Ic/Vce ratings) can be used in to achieve optimal performance of the circuit. Like if undercurrent or undervolting a transistor would bring the gain down to 50, which is what a circuit actually performed best with, etc.


Anyway, let us know the part numbers, and maybe you can check out the datasheets and do a little research and figure out for your own knowledge what they can be good for.

If all else fails, find a "booster" circuit like LPB that wants a lower transistor gain, and maybe you have a distortion box on your hands with 'germanium color'. Old LPB circuit that was based on 2n5133 would probably like a germ tran, the new LPB that is a common schematic shows 2n5088 which actually has higher gain than your trans.

I believe, although it's not set in stone afaik, that germanium vs silicon is redundant in anything that doesn't drive hard into clipping. Also, New Old Stock or Old Old Stock will perform the 'magic' better than brand new germanium transistors from radio shack because the design and production process has refined to eliminate most 'undesirable' traits in transistors.

If they're old, make sure those gains are accurate and its not leakage current inflating the real value.

Um, that's about it I guess for what I know about em.

[JebemMajke]

Hoof fuzz?

[lmorse]

I already had a 'man-look' on the web for datasheets, but not found anything yet, all I know about them is.... 11113 CODE ATES SGS MILITARY PNP GERMANIUM TRANSISTOR.

My MK-168 tells me: ICE0=.35mA, hfe=330 vF=186mV

[mac]

A Germanium Big Muff Pi.
Replace those 100 ohm emiter resistors with silicon diodes and tweak collector resistors a bit

mac

[lmorse]

Oooooo! I like the BigMuff Pi! That's a nice idea. You don't have a link to a schematic do you? Could you give me more details about replacing the resistors?

[Kipper4]

easy find @ Tonepad

http://www.tonepad.com/getFileInfo.asp?id=94

R11 R5 R16 are the 100 ohms resistors Mac is talking of replace them with 1n914 diodes and tweek the R4 R10 & R15 if I have it right.

also this
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=38877

Time to get you bread board out.
good luck
Rich

[lmorse]

 

[mac]

R11 R5 R16 are the 100 ohms resistors Mac is talking of replace them with 1n914 diodes and tweek the R4 R10 & R15 if I have it right.

Yeap.

For the last stage, it is easier to tweak R20 until collector is at about 4v to 5v, than adding a diode.



Germ BMP sound demo

mac

[lmorse]

Cool, nice sound demo - I'm gathering the parts now!

[lmorse]

Can you explain why the resistors are swapped out for diodes?

[mac]

In the silicon version, the voltage across the 100k, or 82k depending on the version, from base to ground is given by the silicon transistor base to emiter voltage drop, Vbe, and a tiny voltage across the 100 ohm resistor. Vbe is about 0.6v when the transistor is fully on.
That is,
V(100k) = Vbe + ie*100
Neglecting the 100 ohm resistor, the 100k sees a voltage of 0.6v or so. The current across this resistor is 0.6v/100k = 6ua.

If you put a germ in there, Vbe(g) is 0.1v - 0.2v, the 100k current is less and the collector will sit far from the original point, about 4v or so.
When you replace the 100 ohm resistor with a silicon diode, you add extra voltage to Vbe(g), being the sum about 0.5v - 0.6v.

If you don't want to use a diode, you need to lower the 100k to about 15k because Vbe(g)/Vbe(s) is roughly 1/6.

mac