kustom k100-0 pc103 driver transistor substitution help.... HELP

[supawah]

okay, here's the beast. Kustom k100-1 with pc103. I need to substitute for q121 38869, q122 38870, q123 2n3567, and q124 2n3638. what's something I can get at mouser? 2n3044? compliment? any ideas? I suck at substitution. thanks

[soundguruman]

38869= NTE 128
38870= NTE 129
2N3567= NTE 123
2N3638= NTE 129

So you see, 38870 can be replaced with 2N3638, etc...
Some people frown on NTE parts, but I have found that they work just fine. The part is only as good as the tech who troubleshoots and installs it.
And many people have blamed their lack of ability on the parts, but it's not the parts fault usually.
It's more likely the lack of troubleshooting other defects in the circuit...that fails to fix the real problems.
And it's convenient to blame NTE, but that's not usually the real cause of failure, just a scapegoat.

[The Dude]

First, I'll say that I have nothing against NTE parts for some things- not all. There are some critical circuits where a substitute just won't work correctly. For instance if you're replacing a single output transistor in a group. I'd prefer an OEM part so that things stay better matched.

Secondly, "crossing a cross" is not a good idea without some additional research from looking at data sheets. Here's why, for example. Let's say that "Transistor A" /the original part is rated at 2W. We cross it to an NTE part ("Transistor B") that is also rated at 2W. We then find another part ("Transistor C") that crosses also to "Transistor B"/The same NTE part. However, it is rated at 1W. Remember these are substitute parts so as long as the max ratings are equal to or above the original, they are generally considered acceptable by companies such as NTE. So we end up with a part that is rated at half of what it needs to be.

In short (because it's confusing):
In the example both "Transistors A and C" cross to "Transistor B". However, Transistor C is rated for half the power of the others.

I'm not saying don't do this. It's a worthwhile tool when necessary. But it is just that- a tool. You need to compare specs on datasheets to make sure the replacement part will work and stay working.

[Enzo]

NTE parts are crude approximations to the real parts they substitute for. It is only the flexibilty of the average circuit that lets you get away with NTE parts.

If you have a row if output transistors in parallel, as you will in most large power amps, NTE will cross the transistors. But if you insert one NTE in a line of say Motorola parts, it will have been made on a different line by a different process. So you cannot trust it to track well in terms of gain or more importantly thermally. You can wind up with an NTE transistor that either hogs the current or one that never turns on as hard as the others and so is not up to the task. This is important, hell even the Peavey replacement guide warns against mixing transistor brands.

NTE parts as a rule cost three to ten times more than the parts they replace. That is a hell of a price to pay for a little printed baggie around it.


As Dude points out, NTE might offer up one sub that covers a 20v, a 30v, and a 40v transistor. So you can never assume that if all three cross to the same NTE that they are also the same. They are not.

A famous example of the NTE problem is crossing the old RCA 40409 and 40410 drivers. NTE will cross them to some NTE types, but the main feature of the 40409 and 40410 is that integral heat sink. The NTE parts DO NOT have that heat sink, so if you just solder in those "replacements" they will soon burn up.

The advantage of NTE is that a local store can stock a few hundred NTE types, and via the magic of the cross refernce book, replace THOUSANDS of transistor types. The disadvantage is that THOUSANDS of transistor types are being replaced by a small number of NTE parts. And local technicians can grow up never learning that difference.

[soundguruman]

First, I'll say that I have nothing against NTE parts for some things- not all. There are some critical circuits where a substitute just won't work correctly. For instance if you're replacing a single output transistor in a group. I'd prefer an OEM part so that things stay better matched. Secondly, "crossing a cross" is not a good idea without some additional research from looking at data sheets. Here's why, for example. Let's say that "Transistor A" /the original part is rated at 2W. We cross it to an NTE part ("Transistor B") that is also rated at 2W. We then find another part ("Transistor C") that crosses also to "Transistor B"/The same NTE part. However, it is rated at 1W. Remember these are substitute parts so as long as the max ratings are equal to or above the original, they are generally considered acceptable by companies such as NTE. So we end up with a part that is rated at half of what it needs to be. In short (because it's confusing): In the example both "Transistors A and C" cross to "Transistor B". However, Transistor C is rated for half the power of the others. I'm not saying don't do this. It's a worthwhile tool when necessary. But it is just that- a tool. You need to compare specs on datasheets to make sure the replacement part will work and stay working.

Of course you have to study the specifications...the part is only as good as the tech who installs it. As far as NTE parts go, I have never had a single unit returned by a customer because of NTE parts that were used in it. I'm still waiting....it's been quite a lot of years... and so I have nothing bad to say about the reliability of a properly selected NTE substitute...when properly installed, they work, and keep working.
I repaired a Randall amp some decades ago, when I was twenty something years old... and it found it's way back to me recently.
I used ECG/NTE parts, and lo and behold decades later, they were still working just fine.
So perhaps the "crude approximation" was good enough?

Otherwise the amp would have probably become trashed, for lack of original parts. Was it worth fixing? To somebody who used it for 20 years, it was. Did the NTE/ECG parts cost more? Of course they did. But what's $20 for transistors compared to buying a new amp?
The substitute parts saved "somebody" hundreds of dollars!!!

Keeping your old trustworthy amp working for 20 more years? Priceless.

[The Dude]

As Dude points out, NTE might offer up one sub that covers a 20v, a 30v, and a 40v transistor. So you can never assume that if all three cross to the same NTE that they are also the same. They are not.

Wow,......I took the long way around that one, didn't I? Thank you for your much simpler more concise version!

[Jazz P Bass]

NTE's glory days are past.

Before the internet & easy access to datasheets, unless you had every manufacturers data book, it was near impossible to identify parts, let alone find them.

Using the NTE crossreference book was not ideal (can you say swapped pin assignments?) but it was something.

Now we have DSL connections, a nice assortment of suppliers, datasheets galore & MEF.

Who needs NTE?

[soundguruman]

I still use them occasionally...
I rebuilt 2 Hartkes 2 years ago with them. 0 problems since then. (the manufacturer was no help at all with replacement parts)

You need the original type Japanese transistor manual. It has all the stuff you want, so if you can get copies, it's worthwhile.

I still collect the original NTE/ECG books. Lots of them. Valuable stuff, even if you don't buy NTE parts, the information can be quite helpful.

[The Dude]

NTE's glory days are past.

Before the internet & easy access to datasheets, unless you had every manufacturers data book, it was near impossible to identify parts, let alone find them.

Using the NTE crossreference book was not ideal (can you say swapped pin assignments?) but it was something.

Now we have DSL connections, a nice assortment of suppliers, datasheets galore & MEF.

Who needs NTE?

I can tell you who. Almost nobody! I used to be an NTE dealer. With the internet came easily searchable parts at affordable prices. Sales dropped to the point that it wasn't worth the effort. DONE.

There were times, if in a rush, where I'd use an NTE part if I needed something done NOW and didn't have the OEM around. Nobody sells NTE, ECG, or the like in my area any more so if I'm gonna have to order something and wait anyway, I might as well order the cheaper/more correct part rather than order a sub.

I agree with soundguruman in that there's nothing wrong with NTE parts themselves as much "legend" has it. The problem is with people using the wrong parts for the wrong job or crossing incorrectly- without reading specifications (which are readily available for all NTE parts). And, lets face it. Much of the time having the exact part is not that critical (whilst sometimes it certainly is).

[Enzo]

The only place NTE makes any sense is for a local parts dealer to stock them. There is no point in ordering them. If you have to order something, then just order real parts.