The Chase for GE transistor

[EGRENIER]

So, I have a PCB for a twin face and of course I'm not able to source AC128 from my regular sources. I started looking at potential replacement and saw that there's tons of options. But, I'd like to stick with Germanium for the PNP side.

Did some research and it appears that Ebay is pretty much the only place to find some. I found a seller, tons of inventory, 99.9% positive feedback, the only problem, he seems to be in Ukraine.

So my question is: Anybody ordered parts from Ukrainian sellers lately ? With the war raging, did you get your order ? Was it delayed ?

TBH, with the current context, I would love to help a Ukrainian seller and give them some business, but I'd also like to know if I will receive the trannies...

Any comment welcome !!!

 

[giovanni]

What hfe do you need? If I have them and you’re in the US I’m happy to send you a few. PM me.

 

[EGRENIER]

What hfe do you need? If I have them and you’re in the US I’m happy to send you a few. PM me.

That is a very good question

I'm not that knowledgeable on Hfe and leakage.. So I'm not really sure what would be best for the Twin Face circuit. However, everything I've read for a fuzz face based on GE is that Hfe is not the main factor, low leakage is ? I could be wrong as I'm learning this as I go.

HFe for AC128 specs are between 55-175, so I would guess any matching pair around 100-120 would be good ?

Sadly, I'm in Canada, but your offer is greatly appreciated.

 

[Chuck D. Bones]

For FF, the "usual" HFE is 60 - 100 for PNP1, 80 - 120 for PNP2. There is no magic HFE or part number, so socket & experiment.

I'm sure there are some Canucks on these forums who can spare a couple PNP Ge trannies...

 

[Oh_Discordia!]

I’ve ordered some from Ukraine via ebay. Some a few days after the war started and some about 2-3 weeks ago. First order got here (US) in about 5 weeks. Still waiting on second order.

 

[pcb rookie]

That is a very good question

I'm not that knowledgeable on Hfe and leakage.. So I'm not really sure what would be best for the Twin Face circuit. However, everything I've read for a fuzz face based on GE is that Hfe is not the main factor, low leakage is ? I could be wrong as I'm learning this as I go.

HFe for AC128 specs are between 55-175, so I would guess any matching pair around 100-120 would be good ?

Sadly, I'm in Canada, but your offer is greatly appreciated.

I ordered some from Ukraine a couple days ago. I did get a noticed that they have shipped.

If I do get them, I would be happy to send you a set. If I don't get them, well it's too bad for me and you but I'll just tell my self that I have shared a couple of dollars to someone that probably needs it more then ever these times and days.

 

[pcb rookie]

I ordered some from Ukraine a couple days ago. I did get a noticed that they have shipped.

If I do get them, I would be happy to send you a set. If I don't get them, well it's too bad for me and you but I'll just tell my self that I have provided a couple of dollars to someone that probably needs it more then ever these times and days.

If you are not in a hurry, I'll keep you posted when I receive them. I expect it's going to take a moment or two ...

 

[almondcity]

check out Smallbear?

I've been eyeing some GE transistors for a Gnat build

 

[Oh_Discordia!]

Ive got some MP41 MPA41A MPA42B that are lower gain than the standard FF #'s but still can sound good (IMHO). More than I can use at present, so lmk if anyone needs a few.

 

[EGRENIER]

So I found a local retailer that carries GE transistor... I've decided to take a shot at it and order 60 of 3 different type. According to their site, here are the model and spec of each one. I would appreciate comments, is this stupid or can I get a bunch of GE trannies that could fit in fuzz face or tone bender set up:

• Type Designator: 2SB187
• Material of Transistor: Ge
• Polarity: PNP
• Maximum Collector Power Dissipation (Pc): 0.2 W
• Maximum Collector-Base Voltage |Vcb|: 25 V
• Maximum Emitter-Base Voltage |Veb|: 12 V
• Maximum Collector Current |Ic max|: 0.15 A
• Max. Operating Junction Temperature (Tj): 75 °C
• Transition Frequency (ft): 1 MHz
• Forward Current Transfer Ratio (hFE), MIN: 100
• Noise Figure, dB: –
• Package: TO1

• Type Designator: 2SA12
• Material of Transistor: Ge
• Polarity: PNP
• Maximum Collector Power Dissipation (Pc): 0.08 W
• Maximum Collector-Base Voltage |Vcb|: 16 V
• Maximum Emitter-Base Voltage |Veb|: 1 V
• Maximum Collector Current |Ic max|: 0.015 A
• Max. Operating Junction Temperature (Tj): 75 °C
• Transition Frequency (ft): 3 MHz
• Collector Capacitance (Cc): 12 pF
• Forward Current Transfer Ratio (hFE), MIN: 70
• Noise Figure, dB: –
• Package: TO1

• Type Designator: 2SB22
• Material of Transistor: Ge
• Polarity: PNP
• Maximum Collector Power Dissipation (Pc): 0.17 W
• Maximum Collector-Base Voltage |Vcb|: 25 V
• Maximum Collector-Emitter Voltage |Vce|: 25 V
• Maximum Emitter-Base Voltage |Veb|: 12 V
• Maximum Collector Current |Ic max|: 0.075 A
• Max. Operating Junction Temperature (Tj): 75 °C
• Transition Frequency (ft): 0.4 MHz
• Forward Current Transfer Ratio (hFE), MIN: 95
• Noise Figure, dB: –
• Package: R57

I'm concerned with the minimum emitter-base voltage of 1V for the 2SA12 ? Is that something that should concern me ?

All comments welcome...

 

[giovanni]

That shouldn’t be a problem. The main thing you need is a transistor tester. Measure the transistors and pick the ones best suited for the fuzz in question (typically high hFE and low leakage but I read that some circuits do require some leakage for biasing).

 

[EGRENIER]

That shouldn’t be a problem. The main thing you need is a transistor tester. Measure the transistors and pick the ones best suited for the fuzz in question (typically high hFE and low leakage but I read that some circuits do require some leakage for biasing).

I was thinking of using this method (Extract from a smallbear FAQ):

First, measure the leakage current:



It may take a few minutes for this reading to become stable. (I swear that some of the ones I have tested are reacting to variations in room temp and/or my body heat!) Record the figure on the meter. This is the leakage current.

Keen has noted that too much leakage makes suspect the long-term reliability of a device. How much is too much? My own spec has always been to reject any device that leaks more than 300 microamps at room temp.

Now apply forward base bias through the resistor:



Do the following arithmetic to get Hfe:

(Collector Current - Leakage Current)
__________________________________________________________
Base Current
(all values in microamps)​