2SC2526 Different Versions?

[Bill H]

I just got a Pioneer A-9 that has been worked on. It looks like at one point in time both NPN outputs on one channel were replaced. the #'s on the replacements say 2sc2526 BUT they are 1/2 the size. The originals a 2 bolt through holes and these only have 1. Some one with some knowledge had to do this as they had to re-tap the heat sink for the new output. All the research I did didn't turn up the smaller outputs. any Ideas? I ask because this one side seems to be getting quit a bit hotter that the side with the originals. Maybe there is a mis match between the the Original PNP's and the new smaller NPN's. I haven't checked Bias yet.

BTW... This baby KICK'S A$$!!!

-Bill

 

[markthefixer]

Compare ALL the Veb(operating) as well as the volts across each emitter resistor. Then post....

 

[Bill H]

K here we go.....

On the "GOOD" side:

2sc2526 #1 .643v
2sc2526 #2 .636v

2sa1076 #1 .638v
2sa1076 #2 .628v

emitter #1 142mv
emitter #2 139mv

On to the bad (side that is heating up)

2sc2526 #1 .562v
2sc2526 #2 .556v

2sa1076 #1 .663v
2sa1076 #2 .609v

emitter #1 300mv ------ No Kidding
emitter #2 116mv

 

[markthefixer]

Turn it DOWN no kidding...

Any questions? The numbers do speak for themselves...


BTW by my count, there are 4 transistors per stage, yet there are only two readings, was this across BOTH emitter resistors?

What were the output offset voltages?

 

[markthefixer]

Are both the case styles marked 2sc2526? If so, I wonder if you got some counterfeits? Pictures would help, but I suspect you got some TO-3P cases.

I have not finished the work yet, but I am substituting TO-3P MJL3281 and MJL1302 's ($3.50 each...) for the RM-60 2sa1076 & 2sc2526 transistors in the SX-3900. (if their bigger brothers are good enough for EW's SX-1980 restoration, they're good enough for me)

But your heatsink may have a ridge in the mounting surface that prevents that substitution, then you would need to see if ampslab.com's MT-200 2sa1216 & 2sc2922's will fit. They sell a set of 4 for 30.00, or two complementary pairs for 30.00. Or get the heatsink's ridge machined down...

I have absolutely no idea what type of transistor would be a full 0.1 volt LOWER in Vbe(under bias) than the originals

 

[Bill H]

Yes Mark you are correct, they are TO-3P cased and they do say 2sc2526. I dont know what to make of it. I would have to have to re tap the hole heat sink for a new transistor. Are there any replacement 2sc2526 that anyone is making? The emitter resistors are a 3 pin unit with the center connecting to the output. My readings were across the whole unit .47+.47.

How would the 2sa1216 & 2sc2922's preform compared to the originals? Looks like the way I might like to go.....

 

[markthefixer]

Yes Mark you are correct, they are TO-3P cased and they do say 2sc2526. I dont know what to make of it. I would have to have to re tap the hole heat sink for a new transistor. Are there any replacement 2sc2526 that anyone is making? The emitter resistors are a 3 pin unit with the center connecting to the output. My readings were across the whole unit 4.7+4.7.

How would the 2sa1216 & 2sc2922's preform compared to the originals? Looks like the way I might liek to go.....

The to-3p cased transistors marked 2sc2526 have a VERY high probability of being counterfeit. I don't know if the 2sc2526 number has "gone generic" legally yet.

The 1216 & 2922's are from a reputable supplier and the specs are comparable and compatable to the originals. The only question is how the case configuration will fit on the heatsinks, especially with regards to available FLAT surface and mounting holes.

Unfortunately the original's (2625) case style has gone out of favor, (too expensive to manufacture?) and the few REAL ones that are left or available go for a premium, thus the danger of counterfeits...

The best thing to do is to adapt to a common modern (TO-3P) case, and go with a reputable supplier of a modern and quite robust transistor set (onsemi MJL3281 and MJL1302 in TO-3P) and never have to worry about it again.

 

[Bill H]

Point taken! I can put MJL3281 and MJL1302's in use and all I would have to do is re-drill the sink which is what I would have to do in any case. Where are you getting yours? I hope they make it sound just as good. I want to get this puppy running. after getting a taste of it last night I can't wait!!

And most of all what is the best way to tap new holes in the H/S

 

[markthefixer]

I just thought of something: the bias is SPLIT between positive and negative on this amp, try using the bias procedure on page 12 of the pdf and see if you can dial the numbers in correctly. After it has a chance to thermally stabilize in a normal physical operating configuration, recheck the bias for drift and readjust if necessary.


At mouser.com

863-MJL1302AG pnp TO-3P bce 260V 15/30A 200W 45-150 30MHZ $3.50 ea
863-MJL3281AG npn TO-3P bce 260V 15/30A 200W 45-150 30MHZ $3.50 ea

I use USPS first class shipping at 4.00 or USPS Priority at 6.00 depending...
UPS goes 6 to 8 bucks and seems slow.

IF you change them, when you get them in, check for shorts and use a dim bulb tester for initial powerup, and start the bias procedure as printed in the manual.

I generally completely remove the heatsinks and take everything off. Of course, I have a drillpress....

 

[Bill H]

I tried the biasing process and it still gets IMMEDIATELY HOT. While were at it, I should replace the Drivers as well. what do you recommend for that? I do have access to a drill press. How do I properly thread new holes?

It looks like the drivers are 2sc2275a & 2sa985a

 

[Bill H]

How about these for drivers.....

http://www.onsemi.com/pub/Collateral/MJE15032-D.PDF

The MJE15032 & 33. Same family. what do you think. While I'm in there, I might as well clean house on those boards.

 

[markthefixer]

Those are a good choice, but if the originals are working, might as well leave them alone.

The only thing I would do is check the heatsink greasing and insulators.

This style of amp seems to be very intolerant of unmatched outputs.

 

[Bill H]

Bring up an old thread.......

After a year in pieces, I'm gonna finish this one! I have the new outputs (on Semi). You were correct, there is a ridge in the heat sink. What is the best way to get rid of it? I was thinking grind it with a dremmel. Then it needs new holes. I dont have a hole tapper but it looks like the last guy just drilled the holes and tapped it with the screws. What's the best way to do this?

 

[markthefixer]

I'd use the dremel, and confine myself to the ridge. It will never be as flat and smooth as the rest of the mounting surface, so do your best effort to make sure it doesn't interfere (stand proud of the surface) with the rest of the transistor and heat sink mating surfaces.

Then I would use a high quality sil pad (instead of mica) AND thermal compound for the best possible heat transfer.

Get the correct drill bit size for the tap, and a tap and do it right. The extra effort and time is worth it, and with fleabay, one off drill bits and taps aren't hard to find.

Of course some places do have small kits with several tap sizes, a tap handle and appropriate drill sizes. I got my first small set and much larger second set a long long time ago from craftsman. Don't forget cutting oil - it's very liquid so it can flush out chips.

 

[Bill H]

It's alive!!!!

Thanks to Mark's help..... My A9 is singing once agian...... I replaced all the outputs and a few PS caps. I can't believe how good it sounds!! I was showing my 17yr old son and he noticed it didn't even have a CD input...... I'm putting this guy on Whole House Duty as the Denon does not have the guts for all those speakers.

Thanks Mark agian for all the direction!!

-Bill