Question: Why some transistors and not others...

[Baktown]

All,

Now that I'm starting to get the hang of this (DIY pedals), I have a question about transistors.

Why are certain types used most of the time in circuits I see here?  I mean, why a 2N3904 or a 2N5088 (for example)?  There seems to be literally hundreds of different transistors made, what is it about these few that DIY builders prefer?

I realize this is a very subjective question, but I started building a transistor cross reference chart tonight, and I realized how similar a lot of these transistors are to each other.

Thanks dudes!

Axl Bundy

[jlullo]

axl,
there are many answers to your question, but in short transistors vary in gain, noise, pinout.... a lot of different things.  Most of the transistor recommendations for pedals here are because of gain....

hope that helps!

Jonathan

[foxfire]

I realize this is a very subjective question, but I started building a transistor cross reference chart tonight, and I realized how similar a lot of these transistors are to each other.

Thanks dudes!

Axl Bundy

might this cross reference chart be made public someday? i wish i had the patience to something like that.

[foxfire]

oh another reason some transistors might get picked over others is availability. the most common are gonna be the easiest to get.

[R.G.]

We're on about the ninth generation of people in DIY effects that worry about which transistor to use, and so I've typed this about a zillion times now.

Save yourself some trouble and ditch the transistor substitution list. It's just about useless. While there are slight differences in small signal transistors, two things make detailed subs lists useless:
1. Most circuits which use silicon transistors work fine with any silicon transistor of the right polarity you put in there.
2. Most designs had the transistors selected because that's what was cheap and easy for the designer to get.

I encapsulate this stuff in what I call Keen's Second Law - "When in doubt, use a 2N5088."  Or a 2N3904, or a 2N4401, or a BC549, it goes on.

Search for my posts on transistor selection. There's a lot of them.

[Baktown]

Mr Keen,

My question was not meant to dredge up an old topic, I merely wanted to know if there was a reason why certain transistors are used frequently, whether it be due to availability, price, or any other parameter such as low noise, high gain, etc.

I am new to this hobby, and I realize that I ask a lot of questions that seem redundant to an expert such as yourself, but I am by no means ignorant or uneducated.  All I'm trying to accomplish is making sure I have a good supply of transistors in my toolbox so I can build pedals.  I found a local electronics shop that carries NTE components, and when I was doing some cross reference checks, it came to my attention that the NTE substitute for industry standard transistors covered a lot of different transistors, hence the question.

Thanks for your input and advice.

Best regards,

Axl Bundy

[hobojoe]

This is a little off the topic but is the store you get your NTE transistors at MARVAC?

[Baktown]

It's a mom and pop store called Kandarian Electronics in Bakersfield, California.  This place is overflowing with all kinds of stuff, including really old NOS tubes.  I enjoy going in there and hanging out because it's in a really bad part of downtown Bako, and there are some interesting characters hanging around!

Axl

[hobojoe]

Oh, apparently Bakersfield is a little bit further than I thought (thought it was in the LA area) im down in dana point

Sorry for the derail 

[foxfire]

It's a mom and pop store called Kandarian Electronics in Bakersfield, California.  This place is overflowing with all kinds of stuff, including really old NOS tubes.  I enjoy going in there and hanging out because it's in a really bad part of downtown Bako, and there are some interesting characters hanging around!

Axl

wish i had one of those. now i'm all jealous.

[Mark Hammer]

I have an old SAM's transistor substitution/cross-reference guide and a Motorola HEP cross-reference of similar vintage.  The number of substitutions that can be made is mind-boggling...and I don't even think they include Japanese transistors or other non-Anglophone origins.

Sometimes, it's a bit like plastic cutlery or paper plates.  There are a gazillion "brands" out there.  Many are made at the same factory and simply packaged with a different brand name on them or in different quantities for different jobbers.  At the same time, there are also different factories cranking out pretty much the same thing, only in a different location.  Are they ALL the same?  Not exactly.  Some plastic knives will cut a steak and others will snap in two if you try to use them with anything other than shovelling salad onto a fork.  Some paper plates are for one piece of birthday cake, while others will happily carry 3 kinds of salad, meat, AND a potato dish AND second helpings before giving out.  But there aren't 10,000 different specific degrees of quality or usages.  Many different kinds will easily accomplish the same tasks that many others will.

Back when Elektor magazine was focussed mostly on analog, they used to use the acronym TUP-TUN-DUG-DUS in their parts lists for projects.  That stood for transistor-universal-NPN, transistor-universal-PNP, diode-universal-germanium, diode-universal-silicon.  They were able to specify a part as TUN, and a project as requiring 2 TUNs and 2 TUPs and a pair of power transistors, because all these parts were essentially interchangeable with each other.

[Baktown]

Mark,

You just helped prove my theory that everything I enjoy can somehow be equated to food!

Thanks for the info!

Rock on!

Axl Bundy

[GonzoFonts]

I encapsulate this stuff in what I call Keen's Second Law - "When in doubt, use a 2N5088."

LOL, too funny... because its true.

GF

[Pedal love]

It's a mom and pop store called Kandarian Electronics in Bakersfield, California.   
Axl

Bob Kandarian is an old family friend. How is old Bob doing these days? Say hi for me.

[petemoore]

Why are certain types used most of the time in circuits I see here?
  There was a time when Ge would be the certain types you see in all transistor circuits.
  I mean, why a 2N3904 or a 2N5088 (for example)?
There seems to be literally hundreds of different transistors made, what is it about these few that DIY builders prefer?
  Availability at the time, 'better' by far for designers that want to eliminate the need for 'tweekers', they're temp stable, high performance, what more could you ask for?
  Applications...field research, actual schematic availability lends itself to modification, NPN Si's made a great first impression, and they do what they do just wonderful, why Not change active types?
  You would have to learn and research opamps and Mosfets, Jfets if you wanted to try them, opamps require voltage bias components, Jfets and Mosfets can be finicky, the circuits that require NPN Si's are still more plentiful [er...that's getting closer now with ROG and individuals choosing their actives for other reasons than Si component and knowledge and availability.
  I guess by the time Mosfets were available, most people using actives already had experience, schematics, and circuits with bipolars...ie bipolar technology was already 'blooming and seeding' about the time the first mosfet 'seed' was created.
  like dog breeds, they all have a lot in common, and all are distinguishably different.