Low hfe transistor

[jmusser]

Recently, someone was talking about a very low hfe transistor (even lower than 2N2222A) that is supposed to be great for Si Fuzz Faces. Does someone know what it is, or what thread it was buried in?

[MartyMart]

Jeff, 2N2369's are what you're after - I think smallbear has 'em and
perhaps that was the thread ?
Perfect Q1 fodder for a silicon "FF" !

Cheers,
Marty.

[transient]

I don't know if you've seen it, but there's an old thread about piggybacking transistors to get low hfe values. Do a search with the keyword "piggybacking", and you'll probably find it.

...
emre

[Coriolis]

I mistakenly ordered a bunch of 2N3903's (wanted 3904) and recently measured them. I think they were betweeen 60 and 110, so they might be of interest, since they are real cheap and in production.  

Supposedly, there is a pnp counterpart called 2N3905 with hfe in the same ballpark.

[brett]

Some expert will know the deal here, but I *think* that there are 2 classes of low hFE devices:
1.  high speed switches (such as the hFE=70 2N2369A), and
2. power devices (from 10A current-handling hFE=50 MJE3055 to the 1A hFE=150 BD139)
Given the large number of power devices, it's wonder they're not used more.  They might even lose that christian radio from your fuzzface due to their low FT.
cheers

[petemoore]

1. high speed switches (such as the hFE=70 2N2369A)
 I have a batch of these on the way from SB as I type, hoping they'll arrive today !!!  
 If you're building an Si FF, these transistors are a good thing to have around...there are others and other ways of course.

[petemoore]

If you're perfing and want to PiggyBack [thanks to Brett IIRC For the PB trick], see FF TWEEK posting, it shows the 8pin IC socket method I came up with for easily implimentation and use of this mod, you can plug in transistors and easily change Emitter to Emitter resistors.

[Michael Weidenauer]

I like the 2N2906 for SI-Fuzz Face Clones.

[petemoore]

I like the 2N2906 for SI-Fuzz Face Clones.
 THe Data sheet 'say's there should be some good ones for FF Q1...

[R.G.]

[thanks to Brett IIRC For the PB trick]

Actually I came up with the idea for piggybacking to reduce hfe, but Brett did do a large amount of development on it and posted on it a lot here.

[rodriki1]

have thought about tip31.
may sound good...

[petemoore]

[thanks to Brett IIRC For the PB trick]

Actually I came up with the idea for piggybacking to reduce hfe, but Brett did do a large amount of development on it and posted on it a lot here.

I'm trying...thanks are in order for this knowledge, thanks to RG and Brett for the piggyback technique knowledge/technique of Q gain reduction, this might be something a pot could control on Nurse Quacky or any circuit that responds to 'finely tuned small gains'.

[jmusser]

Thanks gentlemen! I knew there was one somewhere, but it wasn't the post header, so it was just buried in some othere thread that veered a little. I doubt very much that I have 2N2369As around, but the 2N2906 rings a bell. I believe I have a pretty good batch of those that I was given. I may even have the other one by some fluke, because people are always giving me stuff. I have some buddies who do othere electronic things, and have collected a lot of stuff that's out dated and of no use to them anymore. Of course that's just perfect for our use. I need to get me something with an hfe checker. I recently stripped out hand fulls of C1345, C1344, B726, C732, 2N4249, SPS953, etc. , and a lot of them reference out to NTE123AP (2N5088 types), and NTE159 (2N5087 type) transistors. Since I have the 2N2369 number now, I'll run it on NTE, and see if it comes out to anything I have stuffed in a drawer.

[Stevo]

To pull teeth here I have something of interest  You know those very low germanium trans you end up with.... well build a LBP-1 out of two of them in a darlington set-up..Works really good and add a 22uf cap emitter to ground parallel to the resistor makes a real cool overdrive and is well in the ballpark of an excellent rangemaster :shock: You wil need a volume pot 100k at the end...I have done a bunch of these with 50 hfe and you should really like the sound.... kind of hard to put away for me

[jmusser]

I never thought of using low hfe germs in a Darlington pair, but it certainly makes sense to me. Especially when you have several out of range. I mean, what else are you going to do with them otherwise, except maybe use them for diodes. Ok, I just mentioned a whole bunch of salvaged Si transistors above, and how they came out in the cross reference to a NTE123A. Well, as it turns out, the really low hfe transistors like the 2N2369, and the 2N2906, also end up being NTE123A!  :? So, what good is the NTE Cross Reference? I guess I know they are Si PNPs, but that's all I know. This means they can have an hfe from 50 to 850, and they're all heaped into the same category, so you could have a barrel load of NTE123A, and only one out of 5 billion that you could actually use for a specific circuit! :shock:  Now that's handy! :roll:

[Stevo]

When you check the trans against hfe the NTE cross reference is a joke...Go buy what you have not the cross reference..I dont know why but everything is a NTE 123A or NTE123AP if it is NPN, it does not make sense.

[R.G.]

Actually, it does make sense, if you are doing what NTE is doing. They are trying to replace a largish number of types with a few types, and have those substitutions work.

That works fine for almost all circuits - except ours. 99.99% of all transistor using circuits have been designed to NOT care what specific transistor characteristics are in there. It's that self defense that engineers developed against variable transistor values.

If you'll search the forum, you'll find me saying this many times - for the vast majority even of FX circuits, the transistor type number does not matter.

There are a few circuits, the FF being notable among them, where the detailed transistor gain matters. That is a tiny, tiny minority. It's less than invisible to NTE. They are trying to make the professional repair people happy with replacement parts. They don't (and *can't* from an economic standpoint) care about transistors to make FF clones.  

This is not because they are an uncaring corporate giant, bent on raping the planet and crushing the little people under their hobnailed boots (however big they really are), it's because they are frantically trying to make money in very competitive business space.

Just because someone rolls a steamroller over you does not mean that they have any ill will for you - they may well be *unable* to see you.

[Eirik]

Stevo wrote:
To pull teeth here I have something of interest Very Happy You know those very low germanium trans you end up with.... well build a LBP-1 out of two of them in a darlington set-up..

How would I connect two PNP's to get a diy darlington?
I tried to search, but I wasn't able to find anything corvering the topic in detail.. Only the NPN darlington.

[petemoore]

Loooking at Jfet example...
 MPF102 compared to J201 this way...
 how much gain does an MPF make compared to a J201...3/2 ?  4to5?
 IOW for a seriesed gain stages proposition adding in an 'extra' MPF102 stage on an otherwise 4 stage affair with J201's...what's the 'gain ratio' between these two? J201 has more but how much more?
 Then there's the question of Gain Vs. Noise...is a 5 stage mpf cct inclined to be inherently noisier than a 4 stage 201 experiment?
 Simplicity and utility, aslo fewer parts per build has created a lean towards starting with j201's or 2n5457's...with suggestions that MPF102 be subbed in.
 I'll bet there's a reasoning behind the MPF102, I'm thinking it's smaller gains spread over more stages to get 'the same thing only different'.
 I typed this in interest to see results where higher gain Jfets are like Kiwi Fruit in the artic.

[Stevo]

To make a darlngton set-up connect the collectors, emitter from the first one goes to the base of the second one... The second has its own and only emitter now sharing the collector with the first..To say again connect the emitter of the first transistor to the base of the second transistor connect the collectors....Easy??? npn pnp either way but the voltage hookup is different.. I meant to say about an LPB-1 is add a 1k resistor to the emitter with a 22uf polarized cap in parallel..you will have good gain this way you can also use a trim pot 10k on the collectors to really dial it in....Try this with your junky germaniums that have low hfe they will sound like a germanium booster circuit now