Replacing burned out transistor

[DeadSpeaker]

Hi I'm working on the Project 27 from Rod Elliot. I made a mistake and burned out a BD139 on the power amp board. I'm hoping to get this thing done before not too long and was wondering if I could use a transistor from Radio Shack. I picked up a MJE3055. Is that too powerful? Thanks

[AndrewT]

completely different parameters.

[Original Burnedfingers]

The BD139 should cross to a 2sD669 provided that I am correct in assuming it is a TO-126 case.


It is available from MCM electronics for less than $2.00

[DeadSpeaker]

ahh ok thanks. I guess I'll be placing an online order.

[DeadSpeaker]

I found a local store. They cross referenced the BD139 to a NTE184. Their specs are similar.

BD139
http://www.futurlec.com/Transistors/BD139.shtml

NTE184
VCBO 80V
VCEO 80V
VEBO 5V
Lc 4A
Pd 40W
hFE 7Min
fT 2MHZ Min

Any idea about if it will be all right in the Project 27?

[pilli]

...you may find inspiration here, for example:

BD139-16 & BD140-16? Anyone use these transistors?


_

[anatech]

Hi Fellas,
Please avoid using remarked parts, such as the NTE part that was recommended. The originals are easy to pick up and are cheaper. Then you also know exactly what device you have. A part of this type will be popular in many projects, so having more is a good thing.

-Chris

[unclejed613]

NTE parts are usually adequate for general purpose repairs, and usually exceed the specs of the original part with Vce and Ic and Pd, but if you're using it in a diff amp, current mirror, driver or output stage, theyre not really very good for that, because they will be mismatched (unless you replace these devices as pairs with matching NTE parts, which gets very expensive very quickly). NTE parts are usually twice the cost of original parts, and NTE parts dont neccesarily match or exceed other parameters for the devices they replace, such as Ft and beta. thats why they are "Replacement Parts". theyre used for repairs where "close is good enough", but not where you must have an exact replacement.

[DeadSpeaker]

Well I have the part installed and a couple other parts have been replaced. Other parts seemed to test out fine. I'm gonna install the safety resistors and power up!

[anatech]

Hi unclejed613,
Hmmmm, old post. Sorry, but I want to clear something up.

NTE parts are usually adequate for general purpose repairs

Nope, they aren't. The problem is that you have no idea what the original part is, or it's exact characteristics. Their subs are sometimes in error as well.

because they will be mismatched (unless you replace these devices as pairs with matching NTE parts, which gets very expensive very quickly)

I only wish this were the case. There is no such thing as NTE matched parts in reality. Often, those parts are mixed from different run numbers at the OEM. They may also be mixed form different manufacturers on top of that. You have no realistic hopes of obtaining a matched pair with NTE or ECG.

and NTE parts dont neccesarily match or exceed other parameters for the devices they replace, such as Ft and beta.

Since they may not even be the same part, not much can be counted on being the same. I've also had higher failure rates when I was forced to use ECG parts, and I see a high failure rate in equipment that comes in for service. If I see an ECG or NTE replacement part, they need to be replaced. Period.

thats why they are "Replacement Parts". theyre used for repairs where "close is good enough", but not where you must have an exact replacement.

Actually, there is no excuse for using these darn things. There is no repair that "close is good enough". No such thing. If you don't have the exact part, a good technician is capable of making a more intelligent substitution with real parts. I don't classify ECG or NTE as real parts. They are "remarks" or fakes. Just imagine if fake parts got into that supply chain. If they haven't already.

I'm sorry to have had to disagree with you on this unclejed613. There are no good service technicians that will use these things. people who use them only think they are good, or they are forced to use them from management.

-Chris