Germanium - GT404D, GT404J

Barcode · Post by **Barcode** » 15 Nov 2010, 21:44

So, on a whim I bought 10 NPN germaniums off ebay. The price was dirt cheap, so I figured I would risk them being usable. However, I'm now having trouble finding the formal data sheet for them, and I'm questioning the pinout.

It looks like the middle leg attaches directly to the case which makes me think that is the emitter, but most Ge devices I've always seen the emitter on one of the outside legs. On the other hand, the Si transistors in my Acoustic 360 are arranged with the emitter in the middle IIRC...

Thoughts? Any leads on a good datasheet? Google turned up nothing. The specs were listed in the auction, so I have that, just not the pinout.

IvIark · Post by **IvIark** » 15 Nov 2010, 21:56

If it's the same as the GT404B then it'll be:

IvIark · Post by **IvIark** » 15 Nov 2010, 21:59

Yes I've found the datasheet for the D which confirms it

Barcode · Post by **Barcode** » 15 Nov 2010, 22:35

AHHH!! Thanks so much! Looks like from the gain specs if leakage is halfway decent these should be good FF transistors, at least for Q1. Also should make a fitting replacement for the 2n1306 in the Acoustic 360 Fuzz section.

Hides-His-Eyes · Post by **Hides-His-Eyes** » 15 Nov 2010, 23:04

let me know what you find, need a couple of NPN Ges.

IvIark · Post by **IvIark** » 15 Nov 2010, 23:28

What sort of gain are you looking for Chris? I've got those MP38A's now and also have a batch of GT404B and AC187.

RnFR · Post by **RnFR** » 16 Nov 2010, 04:31

mark, how do like those 38's? what's the gain/leakage?

just a heads up to you guys, I've had pretty good luck with the Tesla 102nu71's. gainsare around 75, and the leakage is never too bad.

IvIark · Post by **IvIark** » 16 Nov 2010, 08:18

I haven't tried them in anything yet, but the gain range is between 54 and 90 and leakage is all good, with the most being 0.23mA. Out of all the Russian germaniums I've got, only the GT40x have got into the 100s in gain. Out of batches of 50, the GT402B PNPs were between 78 and 193 with only 7 below 100, and the GT404B NPNs were from 61 to 170, with 23 below 100. The NPNs have much worse leakage though.

For other germaniums, I've just ordered a batch of 2N404s so I'll let everyone know how they turn out.

IvIark · Post by **IvIark** » 16 Nov 2010, 08:27

Actually thinking about it I'm pretty sure a lot of the mini-germaniums I bought, the GT108G and GT309B were over 100. I didn't test them all and record the numbers though so I'm not sure what the spread was like.

Hides-His-Eyes · Post by **Hides-His-Eyes** » 16 Nov 2010, 10:39

IvIark wrote:What sort of gain are you looking for Chris? I've got those MP38A's now and also have a batch of GT404B and AC187.

I'm not too fussy; something between 60 and 100 and something between 100 and 150? It's for a FF that'll have both Q1 and Q2 switchable between that and BC108Cs, although I haven't decided if I'll stick that hollis autobiaser in there or not...

RnFR · Post by **RnFR** » 16 Nov 2010, 11:40

IvIark wrote:Actually thinking about it I'm pretty sure a lot of the mini-germaniums I bought, the GT108G and GT309B were over 100. I didn't test them all and record the numbers though so I'm not sure what the spread was like.

well, that sounds promising. I'm guessing the leakage isn't that bad?

DrNomis · Post by **DrNomis** » 16 Nov 2010, 12:14

RnFR wrote:
IvIark wrote:Actually thinking about it I'm pretty sure a lot of the mini-germaniums I bought, the GT108G and GT309B were over 100. I didn't test them all and record the numbers though so I'm not sure what the spread was like.
well, that sounds promising. I'm guessing the leakage isn't that bad?

I've never built anything with GT404 transistors before,nor was I aware they existed....

IvIark · Post by **IvIark** » 16 Nov 2010, 15:12

Hides-His-Eyes wrote:I'm not too fussy; something between 60 and 100 and something between 100 and 150? It's for a FF that'll have both Q1 and Q2 switchable between that and BC108Cs, although I haven't decided if I'll stick that hollis autobiaser in there or not...

I'll send you a PM

IvIark · Post by **IvIark** » 16 Nov 2010, 15:17

RnFR wrote:well, that sounds promising. I'm guessing the leakage isn't that bad?

The only Russian PNP germaniums that I've bought that have any leakage at all are the GT402B's and they are still all pretty much acceptable levels (only 2 out of 50 were over 0.6mA and the vast majority under 0.3). All the mini-germaniums I measured had zero leakage.

IvIark · Post by **IvIark** » 18 Nov 2010, 16:15

I got that batch of 2N404's that I ordered and I'm really pleased with them. I haven't tested them all, but did about 8 and out of those 5 were between 113 and 150, and 2 were between 150 and 190. The last one was about 440!

I have plenty with the Russian ones to cover lower gain and so really wanted something higher. These were listed as "over 30 hfe" so I really wasn't expecting them to be the perfect range for what I was looking for, but if they keep to a similar sort of range I'll be delighted. Leakage is also excellent. Most had none, but even the 440hfe one only had 0.04mA of leakage.

Post by **azrael** » 28 Nov 2010, 09:59

Which dealer are you buying from?

IvIark · Post by **IvIark** » 28 Nov 2010, 12:47

I got most of the Russian ones from orpheus_2005 and gordelux04, and I got the 2N404s from minifux1