How to identify a good fuzz transistor?

[Paul Corusoe]

I have found a website that shows the specs of different transistors. Here is an example of the info:

Part Number = NKT240
Manufacturer Name = Various
Average Price = 5.73426
Description = Ge PNP Lo-Pwr BJT
V(BR)CEO (V) = 20
V(BR)CBO (V) = 40
I(C) Abs.(A) Collector Current = 1.0
Absolute Max. Power Diss. (W) = 300m
I(CBO) Max. (A) = 100u
h(FE) Min. Static Current Gain = 50
@I(C) (A) (Test Condition) = 50m
@V(CE) (V) (Test Condition) = 0
f(T) Min. (Hz) Transition Freq = 1.0M
C(obo) (Max) (F) = 40p
Package = TO-5
Military = N

If it's not too much trouble could folks let me know what to look for to get great fuzz? I have stumbled on to a nkt254 and 255. They sound great, there is some background hiss but nothing that would stop me from using it. I do notice that on the nkt 254 it has a hfe# 85. Is this a gain number?  The website I found is www.datasheetarchive.com

Thanks,
Max

[jlullo]

max,
hfe is in fact "gain", but the thing is is that Ge transistors have leakage, which renders a lot unusable.  if you get some, make sure to get a bunch so you can test for hfe and leakage.

[enigmur]

It also depends what circuit you plan on building too doesnt it? Some fuzz circuits use higher gain transistors than others.

At the moment Im using a 120Hfe and a 160Hfe in my Fuzz face

[mdh]

Read "The Technology of the Fuzz Face" at http://www.geofex.com/.  It has good information on how to choose transistors, including how to test for true gain and leakage.

[Paul Corusoe]

I have a fulltone 69 with sockets for transistors. Can I tell if it's leaky by looking at the specs? What's leaking and where's it leaking to? I guess I'm looking for guide lines to killer germanium transistors. It's not that I'm not willing to just order and try because I'm already doing that but maybe you could bird dog a couple good uns. 

[mdh]

Leakage is current that flows between the emitter and collector when there's no current to the base, so that the transistor should be off. Probably your best bet for getting good Ge transistors for a fuzz face is to order a set from Small Bear (http://www.smallbearelec.com) or possibly from Aron in the store on this site.  You might want to search for threads on choosing FF transistors, because it is a much-discussed topic around here.  There's lots of good info.  I don't have a lot of direct experience, but I gather that when buying Ge transistors in large batches, e.g., on eBay, you need to be careful that you're not buying a lot that has already been picked through.  Ge transistors vary quite a bit, even within a part number, so data sheets get you only so far.

[Steben]

I never got fuzz faces to work nice with AC125 and AC132, only with AC128. Yet even though one of the original FF families where with AC128 as a coincidence, I won't state you can't make Fuzz Faces with the others. I just had bad luck with those I had. Maybe one of the reasons is that AC128, transistors actualy made for low wattage power amps as in portables, have lower gain than AC125-AC126, which means, they fit better into the stock resistor values of a FF.

An average gain of 50 is rather low. You can trim the circuit to taste, but you will experience less "fuzz" and even bigger tone sucking. Try to select the higher gain part of the bunch.

[smnm]

this fine article at geofex tells you how to measure leakage in PNP germanium transistors

http://www.geofex.com/Article_Folders/ffselect.htm

You can get a bunch of transitors and see what you like best, or get pre-selected ones from Small Bear or Banzai. There's a guy on the forum selling AC128s for £0.45 each in the UK - I bought 12 and the are mostly gains of around 50-60, with a few in the 70-80 range. They sound good to me, but I'm not a connoisseur.
70-120 is the range most often quoted as the 'best' gain value for Fuzz Faces. It's a matter of taste, also.

[Paul Corusoe]

Thanks yall! I have read the Geofx piece on the fuzz face. I am trying to understand. Some of it even though it is simple electronics is WAY over my head. But no worries, no hurries. I'm blessed to have such a cool hobby. Much gratitude for the help.
I ordered some oc44 and oc75s last night from England. Lookin forward to pluggin em in.

[petemoore]

  I've never done the whole transistor checker by the maths method.
  I always just stuck 'em in a FF or TB or RM, and tweeked by ear.
  But that's not complete, I'd stick 'em in the Hfe tester of my DMM, and after testing enough transistors I can truly say that without the transistor math testing I'm in no position to say this works just as good, but it works fine for sorting a handful of transistors...yes I play with bias, gain and the circuit values, but when a 'hot' one comes along, it's easy enough to decide which ones sound good or which ones are hotter than I want in a FF today. That's alot of socket work, if you were making say ten of them, a leakage/Hfe checker build would probably be a time saver.
  I use a 6 or 8 pin IC socket, Q1 on the right side, Q2 on the left, or two 6Pin IC sockets, Input cap and Q1 in the first, Q2 and the output cap on the second, I've not had a sturdiness issue with this method.