What is wrong with NTE transistors?

[Axtman]

I have heard people disparage NTE transistors on this forum. Being a newbie, what is wrong with the NTE brand?

BTW, I am trying to locate IRFP-9140R and IRFP-140R MOSFET output transistors for an Ampeg B-200R amp. Where can I find this transistors?

Thanks!

[Jazz P Bass]

There is not a thing incorrect with NTE parts.
What is 'wrong' is that they are not an 'exact' replacement.
They group items under one number.
Also you have to be carefull that the pinout diagram is the same or you will end up twiting the leads to make them work (or insert them & the circuit won't work because of pins in the wrong hole)
Another item to consider is the cost. (but on a one only repair that doesn't fly very well)
As to your MosFets: I like to search Find Chips.com.
It queries the major suppliers.
I had no luck using the dash in the middle or with the R designation.
N will work.
IRFP9140N Stock and Price by Distributor | FindChips.com
IRFP140N Stock and Price by Distributor | FindChips.com

[drewl]

We've been using Findchips.com for many years at work to find all kinds of stuff for the telecom industry, so that's how I discovered them.

Those are pretty common Mosfets, should be easy to locate.

[Amp Kat]

I bet MCM has them and very possibly Digikey.

[Steve Conner]

The "R" devices were an old avalanche-rated type made by Harris. The avalanche rating would never be used in an audio amp, so I think any IRFP140/9140 would do.

Beware matching. If the amp uses several MOSFETs in parallel, I suggest replacing them all at once with devices from the same batch, even if only one has blown. Check the idle currents afterwards to make sure they're not grossly unbalanced.

[Enzo]

Aside from the point made above about not really being the exact replacement, they try to replace 10,000 types with 100products, they are also stupidly expensive.


Let's say you need a can of corn for dinner, you'd like some nice white corn. The grocery store sells that for 89 cents. But you are in a hurry, or it is after the grocer closed, whatever, so you go to the local 7-11 convenience store. They will sell you a can of regular yellow corn - close enough for substitution - and charge you $2 for the can. So you spent twice as much to get something not exactly what you wanted. Buying NTE parts is like shopping for groceries at the 7-11 store. You want a basic $4 power resistor like an MJ15003, and the NTE "equivalent" sells for $12.50. Although for that price you do get a nice printed plastic bag around the part.

The little NTE transistor you stick in place of a 2N3904 will probably be fine. But when it comes to power transistors, you want the whole row of them to be the same type, and one NTE in a row of Motorolas will be the odd duck, and probably will not share current well or track thermally very well either.


If you have a local parts store that sells NTE, the line allows them to stock the NTE selection and "cross reference" them as substitutions for most things. They make the sale. But if you are going to order a part, then NTE serves little purpose. If I have to order an NTE, why not just order the real part?

Mouser has both your IRF types in stock right now.

[Jazz P Bass]

You know, back in the day, before the Internet, it was a real bitch sourcing replacement parts.
Or even looking up data!
Unless you had stacks of manufacturers data books it was a next to impossible task.
Simply grab the NTE (ECG) book, crossreference the part & away you go (unless the pinout is different)
Nowadays, that road does not even have to be traveled.
Online datasheets, multiple sources for parts.
What a good time to be repairing equipment it is.

[Enzo]

I have bought parts since I was a kid, and near Washington DC, I could find parts stores easily enough. Didn;t have transistors then anyway. The first real electronics shop I ran was from 1974, for a place called Music Systems. It was in another industry, but we were getting TTL logic stuff and transistors. I called the nearest Hamilton-AVnet rep and asked if they maybe had a catalog. Hey, what did I know. They said sure, they'd send it to me.

A couple days later this huge box arrives UPS. I mean a box the size of a Mackie powered subwoofer. It was FULL of data books for all the major manufacturers lines. Motorola small signal transistors, Moto power transistors, CMOS and TTL logic chips, SIgnetics data book and a wonderfull applications book. RCA transistors and ICs. Intel and Fairchild made components, and thus had books. The one I liked best and still use is the Motorola component selector guide. I had shelves full of those data books Jazz refers to. But I could find most anything I encountered. Books of diodes, books of connectors - I could find anything Amphenol ever made, I swear. Caps, transformers, you name it, catalogs and data books.

ANd I kept the ECG (now part of NTE) and RCA's SK catalogs handy too. Even if I wasn;t buying an ECG part, the cross ref at least gave me a rough idea what the part was.

ANother book you had to buy was a couple volume set of IC Master. TTL logic chips or dual op amps were easy. But if you came across some 16 pin IC with an od number, you could look up the number in IC master and find data sheets for all manner of stuff.

Yeah, now it is just google.

[Axtman]

Thank you guys for all of your advice!

The amp had 3 out of 4 blown output transistors. The amp had been repaired before by "pros" who have since closed down their repair department and now just sell/rent PA gear. Anyhow 3 of the 4 resistors were the same brand and one was an odd duck. I am going to replace all 4 transistors with the same brand. A repair friend of mine recommended this because he said even the good transistor is probably "stressed". I don't know if I believe him.

I think I found the original problem. The low ohm resistor that grounds the drain was loose from the board. Also one of the driver transistors was loose. Is there anything else that I should check before I fire it up?

[olddawg]

Do you have a variac with a current meter? It's a lot better than crossing your fingers and flipping the power switch. Even a lightbulb limiter is advisable unless you like hearing oonk and smelling smoke. Also don't connect it to a speaker load until you check for dc offset.

[Axtman]

I've got a light bulb limiter and a variac. I make it a habit to bring up equipment slowly on a variac and watch the bulb.

I also check for DC on the speaker.

Yeah I have learned too many lessons the hard way to not play it safe!

Thanks!

[Axtman]

Thank you Jazz P Bass for the link to electronic part distributors.

Which supply house has the best deal on shipping/handling? I infrequently buy parts and also buy in small quantities (under $50). Which distributor will give me the best deal on shipping/handling charges.

Thank you!