Transistor Replacement

[Rectangular]

Hello,  I'm a long time lurker, first time poster

I wanted to know if anyone could recommend a search engine or piece of software to aid in the location of transistor replacements. I'm aware of the NTE replacement finder site, the option available on Mouser's search engine (which usually goes back to nte replacements) , and a series of software packages released in Germany (I forget the name) that are quite pricey but apparently very in-depth.. I was hoping there might be a few other websites or methods I'm  not yet privy to. Usually the drawback I have when cloning an old device is finding the appropriate transistor or OTA (neither NTE stuff or OTA's are available locally)

I appreciate any help,  this is a great forum, and an invaluable resource

-rec

[Seljer]

maybe try the stuff mentioned in this thread here: http://www.diystompboxes.com/smfforum/index.php?topic=48421.0

OTAs seem just the be a pain in general, as I'm not sure if many of the ones that were used in effect pedals (3080s and such) are even still in production (thankfully sites like Smallbear have got a stock of them)

[petemoore]

  If you have a part# to start with/?
 Otherwise the top little blurb on each data sheet provides 'most' of the information you need to do transistor substitutions.
 Do you have a specific need [specification] which needs to be filled by the component?
 What's it going into..what will it be replacing?

[Rectangular]

Seljer  - thanks, that's the kind of stuff I'm looking for,  a good start

Pete Moore -  the list is always changing, I'm often looking at old british and japanese synth/guitar schematics, so right off the bat I have 2S and BC nomenclature differences . Basically I just require as many resources for finding replacements as possible, so that I don't have to keep bothering people every few months with help in locating a rare part.

my current list of specifics is: 2sk30a,  2n4288,  me9002,  bc169c,  bc258b,  and some others I'd have to lookup.. but the idea isn't help in locating specifics, I'm really looking for a "teach a man to fish" solution since the list is always changing

thanks for the quick reply guys !

[petemoore]

2sk30a,  2n4288,  me9002,  bc169c,  bc258b
  These numbers might ring a bell, but not for me
  except I 'think the BC169c is an Si...NTE should have a match...and that data sheet should tell enough about the part to find a suitable substitute.
  I'd punch the numbers in a cross reference and see what that brings up.
   According to NTE:
  Bc169c is like an:
  NTE199
*Silicon NPN Transistor
Low Noise, High Gain Amplifier
(Compl to NTE234)
  I would try an NTE199, 2n5089, or MPSA18, I've found performance varies little [none actually] between these common *Si NPN LN/HG amps. ymmv.
  Here's a great source for the 2n5089's
  http://www.diystompboxes.com/cart/

[Rectangular]

Moore- thanks, I appreciate your help

Perhaps I should clarify further. I am not looking for specific replacements,  but rather looking for various methods of finding replacements.  I was hoping there might be a publically available version of something like the VRT comparison tables ( http://www.eca.de/ )  or that the big wigs (Hammer,  Snowberg, Etc)  out there had some good resources in mind

[petemoore]

  Someone here was discussing and working up to a conversion chart page, I don't know how far that got.
  For the most part just go by the descriptions...or try to look more at the specific applications and determine what will be well suited to them.

[R.G.]

This is a question that vexed me a lot when I was just starting to build things.

Over a long time of messing with this, and over a long time of semiconductor improvement, the answer seems to be evolving to be "Don't sweat replacements. Use what you can get that's reasonably close."

Here's why:
1. Audio is a terribly UN-demanding application for transistors. It's almost impossible to find transistors that don't do audio very well indeed. The exceptions are very old germaniums where you can't get replacements OR originals.
2. Low power audio is a terribly UN-demanding application for transistors as regards power, and effects use doubly so. Well over 98% of all effects are 9V powered. It's hard to find any transistor that won't withstand that. Low power audio and effects in particular rarely use currents over a couple of tens of milliamperes. Driving LEDs and relays are the only good exceptions I can think of and then only for driving multiples. If you build your own linear regulators, you might run into a problem, but three terminal regulators are so good and cheap that it's an exercise in self flagellation to build your own.
3. Most effects circuits have been designed to NOT need anything special from a transistor. The study of how to make transistor characteristics not matter much is one which is (was?) important to get manufacturing yields up. Transistors vary in gain, speed, voltage, etc. within the same type number and within the same device at different currents and temperatures. Designers try to make it work the same whether or not the device varies. Mostly, they succeed.

The bottom line is that you only need a few rules to select your own replacement transistors.

1. Get enough voltage rating. Either read the datasheet for the original part to find BVCeo or look at the power supply for the circuit. Choose a transistor with equal or higher BVCeo or more than 1.5X the power supply for the circuit. With 9V as a power supply it's hard to find devices that WON'T do this.
2. Get enough current rating. For all uses not involving power output or driving multiple relays or LEDs, 10ma max is find, and again, it's hard to find a device that won't do this. Most of the common "jellybean" transistors go up to maybe 50ma or 100ma, so there is lots of room.
3. Get enough frequency response. If you're building most effects circuits, this is trivial. Only worry about this if you're building closed-loop power amplifiers. It's hard to not get enough otherwise.
4. Get low noise if you need it. Memorize a few devices that you can get that have low noise. Mostly, garden variety devices are so good this is not a problem. If you're building moving coil phono preamps or cassette deck preamps, you need GOOD low noise transistors. But mostly, no one builds those things any more.
5. Get the right polarity.

My solution has been to keep about four type numbers of transistors and build everything from them unless it's high voltage, high current, or RF.

This is the reasoning behind Keen's Law: When in doubt, use a 2N5088. There are remarkably few places in effects where a 2N5088 won't do as well or better than the original device.

You can build effects for years with only:
2N5088; alternates are 2N3904, 2N4400, 2N4124
2N4250: alternates are 2N3906, 2N5087, 2N4401, 2N4125.

and a few special devices like germaniums for special occasions, power devices when you want to smell smoke.

[KerryF]

Hey.  This page helps me a bit.  It has some substitues but not all. http://www.kpsec.freeuk.com/components/tran.htm .

Now for my question.  Im about to build an UpOctave.  I need 2N5457s and 2N3904s.  I have the 2N3904s and only one 2N5457.  What else can I used in place of the one last 2N5457?

Thanks

[amz-fx]

You can build effects for years with only:
2N5088; alternates are 2N3904, 2N4400, 2N4124
2N4250: alternates are 2N3906, 2N5087, 2N4401, 2N4125.

In case anyone is taking notes...  the 2N4401 is an NPN device.  The 2N4403 is PNP.

regards, Jack

[R.G.]

Yep. Like I'm always telling everyone else, always consult the datasheets.

2N4400 and 2N4401 are NPN, 2N4402 and 2N4403 are PNP.

'S'wat I get for only using 2N5088s, 2N3904s, 2N5087, and 2N3906. The subtlties slip past me. 

[amz-fx]

2N4400 and 2N4401 are NPN, 2N4402 and 2N4403 are PNP.

The 2N440x series are made on a larger die than the typical 2n390x and 2N508x devices and have a higher Ic rating. They are nice parts and I always keep a few around for when I need something a little more beefy 

Also nice transistors: Toshiba 2SC3329 (npn) and the 2SA1316 (pnp)  Low noise and designed for audio use! very low Rbb'

regards, Jack