Germanium help, Rangemaster biasing.

[JimRayden]

So I took the plunge and bought about 70 germanium transistors, hoping to find a few useable ones. About twenty tested pretty good, rest were either bad or too large to test.

I breadboarded a rangemaster circuit and started to try the tested trannies. The AC188 biased pretty good but I can't get the others to bias or sound decent. I've tried values of all ranges for the resistors but still, the outcoming signal is bassy and weak.

How to bias the circuit if I'm using a transistor of way different voltage and amperage rating in it? Would it be alot different? How much would the resistor values change max? How to figure them out?

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Jimbo

[MartyMart]

Jim, what are they ?
Just "hfe" tested or "leakage" also ?
I bought about 50 Ac128's last year and got less than 8 "good" ones !!
OC44's tested from ebay ... all great
OC140's around 100 and so far most are fantastic .....  Ge's can be a minefield 
Just built a fantastic FF ( Rock Face ) with Russian GT309's which were only hfe tested

Marty

[JimRayden]

Well, let's see.... GT320, P30, GT402, an AC188 and 187. All tested for both hfe and leak. I picked them out considering leakage, but more than half of them have a decent hfe.

I just can't get them biased.  Actually, as soon as I put the 188 in, it biased pretty easily. The rest of them mostly hang around at 4V at collector. (The pin connected to the chassis is the emitter, right?)

Oh, I have one GT309 in that pile too. Cute little saucer.

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Jimbo

[Dragonfly]

The rest of them mostly hang around at 4V at collector.

im just checking...you know to bias a rangemaster aound 7v, right....

im SURE you do....but sometimes i overlook things too....

rock.twang.good.

[JimRayden]

Thank you for worrying but the scentence you quoted was the problem I am stumbling on. I can't get the voltage too much away from the goddamned 4V with the other transistors. I can't seem to raise it to 7V, as needed.

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Jimbo

[MartyMart]

I just can't get them biased.  Actually, as soon as I put the 188 in, it biased pretty easily. The rest of them mostly hang around at 4V at collector. (The pin connected to the chassis is the emitter, right?)

Oh, I have one GT309 in that pile too. Cute little saucer.

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Jimbo

On the 309's the chassis pin is collector !!
GT402's are NPN (GT404 is PNP)
I've had similar problems once or twice and either the tranny was "duff" or
I needed a much larger range from 9v,  50k trimmer  etc ....
Are you sure of the pinout on the "wierd" ones ?

MM.

[Dragonfly]

try using a 100k trim pot in place of the 68k resistor....   

[MartyMart]

My bad .... 402's are PNP  404's are NPN  !!

Marty.

[JimRayden]

try using a 100k trim pot in place of the 68k resistor....   

Already did that. It looks like I'm having problems with identifying the pins...

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Jimbo