Would BD139/140 driver transistors be compatible with MJ21194 as outputs?

62vauxhall

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#1
I dug into an old receiver again that I thought I got working well in 2017. It was doing OK before packing it up for my move in April but it fritzed as soon as I turned it on recently. Blew the main fuse and as near as I could tell, three resistors in one channel got hot, as in at least one was smoking. They have since been replaced.

Between 2017 and now, all electrolytic capacitors have been changed out.

No schematics exist for this thing so in November 2017 I followed an AK thread about a Pioneer receiver with a 2SA497 / 2SC497 pair for drivers, the same as those in my receiver of which one was bad. The thread I was following claimed KSA1220 and KSC2690 were suitable replacements so that's what I used.

All four output transistors mine had were 2CS3055's but from different makers or of different ages so I put in four fresh ones of those as well and like I said, it was good for a while.

Dealving into it again over the past couple of days, I learned that 2SC3055's may not have originally been in this thing but a good possibility they were 2SC1030's. And again, according to an AK thread about 2SC1030's, MJ21194's can replace those.

And I learned that KSA1220's and KSC2690's were not intended for audio.

Four of those MJ21194 outputs are $10 per plus, plus and I would need to order BD139/140 driver pairs. I can get them all from Mouser.ca but would this be a mismatch therefore a waste of money?
 
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62vauxhall

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#3
BD139/140's (TO126) are a different package that an Mj21194 (TO3)
Yes, the TO3's are for the ouputs and the TO26's are for driving them. I have different TO26's in place now, KSA1220 and KSC2690 which I was recently told, were not intended for audio.

What was on the board originally were TO39 packaged 2SA497 & 2SC497 but one was bad. This receiver is quite old.

I am trying for 2nd opinions about the compatibility of using MJ21194's in conjunction with a BD139 & BD140 pair.
 

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#6
KSA1220A and KSC2690A would be my recommendations Gary.

They are indeed audio power amplifier transistors and are properly specified.

Readily available.

Are the final outputs TO-3 and are they complimentary NPN/PNP?

Then again we are shooting in the dark with no schizmo for this device. YMMV.
 

WOPL Sniffer

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#7
I'd try it. The outputs are cheap and as long as you pay attention and scope it, You may be surprised. I used 139's and 140's for something a while back. Still have a couple.
 

62vauxhall

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Have you compared data sheets Gary?
I tried comparing data sheets between those old, original 2SA497 & 2SC497 (or for one of them anyway, the other doesn't seem to exist) and BD139/BD140's. I do not comprehend transistor specs enough to know what's what. Not knowing if higher or lower numbers are good, bad or indifferent is a disadvantage. If there were only three or four "key" specs to focus on and knowing how close original vs replacement numbers need to be, up or down, I might be able to get by without asking questions on forums.

But here I am, asking away.
 

62vauxhall

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#9
KSA1220A and KSC2690A would be my recommendations Gary.

They are indeed audio power amplifier transistors and are properly specified.

Readily available.

Are the final outputs TO-3 and are they complimentary NPN/PNP?

Then again we are shooting in the dark with no schizmo for this device. YMMV.
The TO3 ouputs are quasi-complimentary NPN. And I am committed in that transistors are on order and arriving in 2 to 3 days.
 

62vauxhall

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#10
I'd try it. The outputs are cheap and as long as you pay attention and scope it, You may be surprised. I used 139's and 140's for something a while back. Still have a couple.
Yes, the combo will be tried because they're paid for. But no scope.

No job, supposedly retired and have always lived beyond my means.
 

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#11
Hi Gary
Not knowing the B+ and B- voltage levels in the amp you are working on it is hard to guess but more is better. The BD139/140 are only 80V devices. You need at least B+ plus B- plus 10s of volts of margin. If your supply rails are +/-40V then you have zero margin. The other devices mentioned are 160V devices. Much less likely that you will have a problem.

Also the BD139/140 have no Ft or output capacitance specification whereas the other devices mentioned do, they have an Ft of 150 Mhz. Important for stability.

These are some of the immediate, critical specs that I look at. But again, we have no schematics so are shooting in the dark.
 

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#12
I tried comparing data sheets between those old, original 2SA497 & 2SC497 (or for one of them anyway, the other doesn't seem to exist) and BD139/BD140's. I do not comprehend transistor specs enough to know what's what. Not knowing if higher or lower numbers are good, bad or indifferent is a disadvantage. If there were only three or four "key" specs to focus on and knowing how close original vs replacement numbers need to be, up or down, I might be able to get by without asking questions on forums.

But here I am, asking away.

If it's got 3 prongs.... Yer GOOD :)
 
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