Bad Transistors or....{Solved}

[pryde]

So I bought a couple sets of "matched" NPN germ transistors from an ebay vendor to build a couple fuzz faces for friends. I breadboarded a basic FF circuit to try them out and and getting weird results and would like some insight.

The output signal is very weak and low. I have full signal off of Q2 collector with good sounding fuzz. on the other side of the bias resistor (8.2k on the schematic) is where it drops off. Also to note, in order to get ~4.5v on Q2 I had to use a 39k in place of the 8.2k. However, both values used drop the signal on the other side of the resistor.

I also popped them in my NPN Mangler which is a good working circuit and the sound was gated/crappy.

Any ideas why this is? Are the transistors no good or is my breadboard circuit jacked up, etc.?  thanks for your help. I may need to return these to the vendor if no good.

[midwayfair]

What's your voltage on the base? About half a volt?

39K is really high, even for a germanium transistor, to bias in a fuzz face. However, even if it were very low gain, you should be getting sound.

What's the part number, too?

[sgmezei]

What about the pinout? I have had this happen when I didn't have the correct pinout.

[Pvt. Parts]

I'm going on... you need PNP not NPN for fuzz face.

edit: http://www.theowlnest.com/circuit.html and go to #16

[midwayfair]

I'm going on... you need PNP not NPN for fuzz face.

edit: http://www.theowlnest.com/circuit.html and go to #16

It's an NPN fuzz face. People build them all the time. (It's the ONLY fuzz face I build, personally.)

[pryde]

Sorry fellas, thanks for the responses. I had an overnight Thanksgiving deal.

So, yes the germs are NPN AC176 with T05 package where tab is E. I tried flipping them with the same results?

Volatages are

         Q1      Q2
E       0        .07
B      .07      .10
C     .10       4.68 (with 39k bias resistor)

Any thoughts? Again there is good signal off of Q2 collector and beginning of bias resistor (39k), then very weak, low signal on the other side where it connects with the 470R and output cap.

Thanks for the help

[pryde]

OK it was my bad. Next time I won't "whip up" a circuit at 2 A.M. 

After measuring each resistor in the circuit I had a 1k between Q1 base and Q2 emitter instead of a 100k. I guess that will cause a problem 

After inspecting my 100k bag of resistors I found a few 1k in there. Lesson, always measure before using 

Anyway, the AC176's sound ok, not as nice as my CV7112's but not bad. Only issue is I am getting unity only with the vol pot up all the way. Need to figure this out now?

[midwayfair]

Only issue is I am getting unity only with the vol pot up all the way. Need to figure this out now?

Actually, that's very common with Ge fuzz faces. It depends on a lot of things ... the gain of the transistors, leakage especially on Q1, the phase of the moon. There's a bunch of decent fixes: the easiest is simply to increase the 470R to something like 1K (though I go higher sometimes). It'll boost the mids, too, but not a ton. I used 1.5K in the last Ge FF I actually boxed up and it's outrageously loud (unity is near 9:00 with the fuzz knob up). You could also swap out Q1 for a really low gain silicon and it'll eliminate leakage and temperature drift issues, which might boost the output without changing the frequency response. AC176s are known to have leakage issues ... I'd use the CV's if they sound better.

EDIT: Is your Q1 collector voltage still that low? .5v is normal.

[pryde]

Thanks midway,

I did change the 470R to 1k and that bumped up the output to get unity gain about 2 oclock on the volume pot. The circuit is sounding pretty good as is. THe CV's are in my own FF that I will keep forever as it sounds incredible. I bought a couple sets of these AC176's to have on hand for friends or customers.

Thanks again for the help!

[atreidesheir]

boosted mids on a ff could be a good thing I say.