One thing that I have learnt (the hard way) is that you cannot trust many of the component suppliers and even some manufacturers to give you an proper replacement for the part you already have.
In my case my faithful 200w stereo amp Kicked the bucket a couple of months ago and between my moving to Durban and starting the new job...not much time was spent to attept a repair.
Finally when i had chance to go to the local parts supplier and collect the replacement parts not much thought was spared as to the fact that the replacement might not be compatible.
My 200w amp is based on a 60w TDA7250 Audio Driver driving an ST Microelectronics Darlington Pair (Tip142 + Tip147) and the right channel's Darlington Pair kicked the bucket....no ploblem got some replacements....managed to get ST Microelectronics Tip142's and.... wait for it.... Fairchild Tip147's. Now this is where the problem came in. After blowing the first replacement Tip147 to hell i was much more careful with the second replacement doing several tests, what i've concluded is that the Tip147 (after about 10s) became mild warm and when applying a load on the amp with an audio input @ very low volume made the Tranie even warmer and then cranking the volume past half clock would see some smoke and finally a POP from the Tip147.
Puzzled i traced, checked and re-traced the circuit trying to find the problem but only after downloading and inspecting the data sheet on the ST Tip147 and Fairchild Tip147 i found the problem. Both Tip 147's have two internal resistances and there is an huge difference between the resistances of the two tip147's, this caused an imbalance in the darlington configuration and thus the heat and finally the popping of the Tip147.
So i phoned them up today and asked for replacements but from the ST manufacturer, this proved to be a problem for them as they only purchase from one (major) supplier in the UK and they buy random brands.(this month Fairchild next month ONsemiconductor...)
They could not understand why the Transistors were popping and after some detailed explination and their tech guys looking into the matter they gladly offered to import the "correct" ones for me. (@ a price though)
So just a word of warning - always make sure that the replacements are indeed 100% correct and if possible download the data sheets from the respective suppliers and compare them.
Because i learnt the hard way....even if it says Tip147 and it looks the same, if it's not from the same fanufacturer it's not the same thing altogether.
Below is some of the different types all supposed to be the same thing!
Note that the middle Tranie is in fact a ST Tip142 but it's idetical to the ST Tip147 - the origional one that popped, this is jut to show you how the ST Tip147 looks.
The first one on the left is the second (replacement) Tip 147 that popped!
In my case my faithful 200w stereo amp Kicked the bucket a couple of months ago and between my moving to Durban and starting the new job...not much time was spent to attept a repair.
Finally when i had chance to go to the local parts supplier and collect the replacement parts not much thought was spared as to the fact that the replacement might not be compatible.
My 200w amp is based on a 60w TDA7250 Audio Driver driving an ST Microelectronics Darlington Pair (Tip142 + Tip147) and the right channel's Darlington Pair kicked the bucket....no ploblem got some replacements....managed to get ST Microelectronics Tip142's and.... wait for it.... Fairchild Tip147's. Now this is where the problem came in. After blowing the first replacement Tip147 to hell i was much more careful with the second replacement doing several tests, what i've concluded is that the Tip147 (after about 10s) became mild warm and when applying a load on the amp with an audio input @ very low volume made the Tranie even warmer and then cranking the volume past half clock would see some smoke and finally a POP from the Tip147.
Puzzled i traced, checked and re-traced the circuit trying to find the problem but only after downloading and inspecting the data sheet on the ST Tip147 and Fairchild Tip147 i found the problem. Both Tip 147's have two internal resistances and there is an huge difference between the resistances of the two tip147's, this caused an imbalance in the darlington configuration and thus the heat and finally the popping of the Tip147.
So i phoned them up today and asked for replacements but from the ST manufacturer, this proved to be a problem for them as they only purchase from one (major) supplier in the UK and they buy random brands.(this month Fairchild next month ONsemiconductor...)
They could not understand why the Transistors were popping and after some detailed explination and their tech guys looking into the matter they gladly offered to import the "correct" ones for me. (@ a price though)
So just a word of warning - always make sure that the replacements are indeed 100% correct and if possible download the data sheets from the respective suppliers and compare them.
Because i learnt the hard way....even if it says Tip147 and it looks the same, if it's not from the same fanufacturer it's not the same thing altogether.
Below is some of the different types all supposed to be the same thing!
Note that the middle Tranie is in fact a ST Tip142 but it's idetical to the ST Tip147 - the origional one that popped, this is jut to show you how the ST Tip147 looks.
The first one on the left is the second (replacement) Tip 147 that popped!
