low gain GE transistors- recommendations?

[jdub]

Greetings-

I accidently ordered some low gain trannies from Small Bear (gain 40 & below) and have no idea what to do with 'em.  Anybody have some suggestions for builds where I can use these?  Maybe a booster or something?  Thanks!

[petemoore]

 Seriesed boosters with volume controls, voiced to taste.
  Depending on leakage [related to noise] you might be able to Darlington-ize a-couple, see Bazz Fuss article on how darlingtowns can be made from 2 bipolar transisors.
 

[mac]

if you go for a ge bazz fuss check my mods, leakage can be a problem for biasing ge.
http://www.diystompboxes.com/smfforum/index.php?topic=60531.0

you can try a tonebender 3knob, use the highest gain ge at q3.
aslo a rangemaster if you have some near 50.

mac

[Solidhex]

Yeah

  I was gonna say MkIII Tone Bender as well. Its really forgiving with low gains in Q1 and Q2.

--Brad

[darron]

buffer?
http://www.muzique.com/news/leaky-transistor-buffer/

[slim_blues_boy]

use it for Q1 in Tone Bender MKI, Zonk Machine, even Tone Bender MKII & MKIII.

[jdub]

Wow! Thanks for the ideas, guys.  I've got a half-dozen of these trannies so maybe I can try 'em all! 

[petemoore]

  I found it easiest for me to tell which ones which or how different they are by using 1 in a boost [RM], at a time [rebiased] , amp enough to get wide frequency response, not much room on the body but I laid on paper and took notes [noise, response], tried to get them from low to high gain.
  Used a fine felt tip on 'em to code mark some of them.
  The B/E diode inside the transistor is applicable for clipping OD or distortions, octave, of course anything else that calls for a GE diode.

[brett]

Hi
the main problem with using those for Q1 in a tonebender or FF is the low input impedance, which will wipe your highs. A simple solution is to wire a 10k resistor in series with the base.  Usually, a Q1 with hFE about 70 presents about 20k ohms of input inpedance.  At hFE = 35, you only get half of that, so add 10k.  For 50 to 60, add 4.7k.

For Q2 in a FF you'll have to adjust the bias for Vcollector around 4 or 5 volts (this usually needs to be done anyway, so it's no extra hassle).

Of course, the maximum amount of gain won't be as high as with a higher hFE, but who runs a FF or TB flat out anyway?
cheers

[jdub]

Thanks fer the tips, fellas.  Much appreciated.

[jawknee]

but who runs a FF or TB flat out anyway?

Who doesn't! I say put 10 of those low gain transistors in a series and see what happens.

[darron]

but who runs a FF or TB flat out anyway?

Who doesn't! I say put 10 of those low gain transistors in a series and see what happens.

i agree with that too. most people max out the FF gain knob because you don't get heaps from it and it's very responsive to dynamics. you could even easily eliminate that pot.

[petemoore]

  Calculatin''..not me strong suit..
 But one gain stage, even a mild one, driving another one such like a FF...figure...multiply, then multiply again, the number grows very fast.
 Even if you have to add more stages or use something else [high gainer, silicon for instance] in an early or late stage.
 It might be very nice, some really good sounds come from a series of stages, each contributing a smaller proportion to the distortion pie than say two stages that are hotter.
  Not too terribly tricky but takes some re-working to find 'it'.
  "Slowly growing'' the gain might be one suggestion as an approach to making each successive stage able to contribute.
  Otoh having the 1rst distortable can mean rolloff at the guitar volume can be more of a gain knob, cleaning up more as it's rolled down.

[brett]

Hi
as Pete says, you only need a small gain stage to take a low gain FF (40x40=1600) to a screaming monster (6x40x40=9600, equivalent to the standard 70 x 130).  The BMP works well because it has three mild gain stages instead of two high gain stages (the BMP also has a post-tone recovery stage).
Ideally, you'd use a clean booster (JFET, Stratoblaster?) followed by a transformer (so that the FF or TB "sees" plenty of inductance and capacitance like in a pickup).
High quality Ge devices (almost always Russian or Japanese with only a few uA of leakage) can be made into Darlingtons.  Reduce the gain by adding an emitter resistor on the input Q.
cheers

[petemoore]

  Those Ge's are fun to work with.
 More yet to been done with the low gainers, why not ?
 I can think of reasons why, [expense and trouble dealing with pots, caps, resistors, transistors to name a few], anyone thinking of producing more than 'so many of any transistor type fuzz or boost would naturally opt for transistors which require fewer transistors and other parts to produce, it's simpler to 'tune' or debug decreasing numbers of Ge's.
 Here's a way to get individual Ge reference data [since they do vary] to help design Ge circuit temperature stability: chill the active, put under bias test, warm with thumb and forefinger while continuing to measure bias as the active warms up. Ballpark where the temperature extremes that make it go away from preferred bias, compare to performance environments.
 A hot sun can kill the Tonebender temporarily, so can bringing it in from the freeze.

[jdub]

You know, I was thinking along gain stage/FF lines.  I haven't played with Ge trannies very much, but this is getting interesting & fun...when I get a little time, I gotta hit the breadboard and see what transpires...I'll letcha know\

Great ideas, guys. Thanx

[mac]

i did a 3 stages fuzz for a friend using 2sa101 ge hfe=40 or so.
iirc each stage had a 10k from vcc to collector, 4k7 from emiter to gnd bypassed by a 2.2uf or 4.7uf, 100k from vcc to base, 39k from base to gnd. maybe 0.1uf + 10k between stages. the first two 4k7 were actually pots. no temp problems and a lot of gain.

but who runs a FF or TB flat out anyway?

mmmhhh... me 

mac