PedalPCB source germanium transistors?

[eroots]

I'm thinking about building the Hudson Duocast (among others) which use germanium PNP transistors (specifically the OC71 for the Duocast). I've read elsewhere on this forum that the specific model of the transistor is less important than the specs, and that anything with an Hfe of 70-120 should be fine in this case.

I see that PedalPCB itself sells a few different PNP germanium transistors (1T313A, 1T313V, MP38-40A), but no specs are published on the pages.
Has anyone built using any of these transistors off of PedalPCB? Are the values just within whatever range that specific part usually has, and you have to buy a bunch and test to find the ones that are in range?

 

[Vild]

I haven't built this pedal in particular but from my understanding it's mostly about hfe so generally you can kinda just try whatever pnp germaniums in that hfe you can get your hands on/have lying around. I will say my last batch of about 20 mp38a's from sovcom on ebay all tested between 40-85 so sadly I had no higher ones. Luckily there was a mp20a mixed in that was ~100 so i used it with a mp38a of ~80hfe in my fuzz foundry deluxe last night for example though.

 

[eroots]

Ah OK makes sense. I guess I'll start by buying a few of the MP series and seeing what he I get out of them.

 

[Robert]

Here's a few randomly measured out of the bin with a DCA75.

1T313A
hFE=70 at Ic=5.02mA
Vbe=0.312V at Ib=1.00mA
Vbe=0.403V at Ib=5.00mA
VceSat=0.178V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA

hFE=69 at Ic=4.99mA
Vbe=0.321V at Ib=1.00mA
Vbe=0.405V at Ib=5.00mA
VceSat=0.168V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA

hFE=62 at Ic=5.01mA
Vbe=0.317V at Ib=1.00mA
Vbe=0.396V at Ib=5.00mA
VceSat=0.154V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA


1T313V
hFE=58 at Ic=5.00mA
Vbe=0.323V at Ib=1.00mA
Vbe=0.430V at Ib=5.00mA
VceSat=0.193V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA

hFE=53 at Ic=5.01mA
Vbe=0.322V at Ib=1.00mA
Vbe=0.417V at Ib=5.00mA
VceSat=0.179V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA

hFE=51 at Ic=5.02mA
Vbe=0.323V at Ib=1.00mA
Vbe=0.412V at Ib=5.00mA
VceSat=0.182V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.000mA


MP40A
hFE=39 at Ic=5.02mA
Vbe=0.209V at Ib=1.00mA
Vbe=0.324V at Ib=5.00mA
VceSat=0.042V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.042mA

hFE=38 at Ic=5.02mA
Vbe=0.209V at Ib=1.00mA
Vbe=0.330V at Ib=5.00mA
VceSat=0.046V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.045mA

hFE=32 at Ic=5.03mA
Vbe=0.209V at Ib=1.00mA
Vbe=0.306V at Ib=5.00mA
VceSat=0.045V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.028mA


MP39B
hFE=51 at Ic=5.01mA
Vbe=0.204V at Ib=1.00mA
Vbe=0.299V at Ib=5.01mA
VceSat=0.034V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.050mA

hFE=46 at Ic=5.02mA
Vbe=0.220V at Ib=1.01mA
Vbe=0.341V at Ib=5.00mA
VceSat=0.046V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.036mA

hFE=45 at Ic=5.01mA
Vbe=0.213V at Ib=1.00mA
Vbe=0.337V at Ib=5.00mA
VceSat=0.044V at Ic=5.0mA and Ib=1.00mA
IcLeak=0.044mA

 

[eroots]

Awesome, thanks!

 

[giovanni]

Send me a private message, I have quite a few PNP, I can send you some.

 

[downtofuzz]

Look out for the voltage rating of the transistors since the duocast can switch from 9 to 27V. Some of the transistors you listed can only be used up to 15V. Here is a website to check the specs on https://alltransistors.com/. Maybe consider building a simulcast first since there is more space for a socket so you can test different transistors.

 

[eroots]

Ah good call, thanks for the heads up!

 

[spi]

This is what I used in my duocast (and where I bought it) https://www.amplifiedparts.com/products/transistor-2n404a-germanium-5-case-pnp
I measured it at hfe=200 and 76 mA

 

[eroots]

I measured it at hfe=200 and 76 mA

Whoa that is a high hfe - does it have a ton of gain or does it sound relatively normal (whatever that means)?

 

[spi]

Whoa that is a high hfe - does it have a ton of gain or does it sound relatively normal (whatever that means)?

According to Aion's build doc for the Broadcast:

"Others including the Dual Broadcast use the NTE 2N404A, a new-production germanium that is anywhere from 50 to 250 hFE. The 2N404A taken from a Broadcast in this video measured at 216 hFE with 125µA leakage."

So I guess it sounds "relatively normal"?

 

[eroots]

Ah ok also good to know! For some reason I was under the impression that the range of HFE for the simulcast / duocast was lower than that.

 

[Fama]

According to Aion's build doc for the Broadcast:

"Others including the Dual Broadcast use the NTE 2N404A, a new-production germanium that is anywhere from 50 to 250 hFE. The 2N404A taken from a Broadcast in this video measured at 216 hFE with 125µA leakage."

So I guess it sounds "relatively normal"?

Are there still germanium transistors in active production? I didn't know that.

 

[swelchy]

I heard that @jamesalberton stumbled upon these in his Asia meetings while painstakingly auditioning all of his decommissioned submarine parts. He decided the world needed to hear all of these wonderful " Greenie Sound" producing transistors and decided to have a meeting with NTE @Octaking Labs to strike a sell off deal. So clearly they are new old stock but totally awesome... J/K