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I Really Blew It!!!

KingBubba said:
Detailman, wow! I have thought about trying to describe Skycraft to the folks here at AK but the place is beyond description. What a great place. I go there first before I do anything.
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I thought you might know about Skycrafters. Pretty neat place.
I have not been there for a couple years but when I go I do spend some time there.
Seems like you have gotten some good help from the AK folks and I'm sure you will get it straight.
This is a great place with great people willing to educate those willing to learn.
I'm really hooked.
 
I was adjusting the bias as per the instruction on page 21 of the 9500II SM, or at least I was assuming that it was the bias. The SM did not describe it as such, but I believe that is what it was. There was no instructions for the adjustment of DC offset, but when checked, after the recapping, it was well within acceptable range on both channels, less than .15mv.
 
A company called 1-Source has both of the transistors in stock. They have 13,000 of the 588s and 20,000 of the 618s in stock. The only problem is they only sell to companies. They suggested I call Allied, Mauser, and Digikey which I did with no luck. I then found an archived DIYAudio forum thread about the same amp that showed some other sources. That thread is here:

http://www.diyaudio.com/forums/showthread/t-21812.html

Echowars found the parts for $33 each but the last suggestion was MAT Electronics. They have the 2sb618a for $2.75 each but do not have the 2sd588a. Damn!

Is the A on the end an important factor in these semiconductors?

I also just found this AK thread in archives and the last post showed a possibility for a substitution. Does anyone know if the substitution, that MeAN suggests, will function? I'll PM him if he is still with us.

http://www.audiokarma.org/forums/archive/index.php/t-7203.html
 
Is the A on the end an important factor in these semiconductors?
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Normally it indicates a higher-voltage version of the same part, but the specs I have show no difference in any rating I see...maybe it is a different mounting??

The problem isn't finding a transistor with the proper specs (there are hundreds that would work), but finding a transistor that will mount to the damn heatsink. If you're ready to drill and tap the heatsink, you would have a choice of pretty much any TO-3P transistor you want.
 
Hi guys,
You may also want to look into the NTE2351 and NTE2352. The NTE2352 is a direct cross to the 2SD558, and the NTE2352 is the PNP compliment to the NTE2351. I've had good success with NTE parts as replacements in situations such as this, mostly because the NTE parts tend to exceed the specs of the part they replace. I think they do that to give themselves a margin of error on the good side when cross-referencing, instead of people using their transistors and watching them go up in smoke on first power up.

Also, if each channel has its own fuse, there is a more reliable way to set bias than using test points, if the service manual gives you the actual current draw.

Oh yeah, make sure the bias pots are ok, and clean before putting the amp back together and trying to set things. Don't ask me how I know this . . . :|
 
Those NTE's are piss-poor replacements...not only do they have NO heatsink mounting, they are Darlingtons. They will not work.

(so much for NTE's cross-reference :rolleyes:)
 
A call to Mat electronics showed they had The 618 in stock but not the 588. On the website it shows both in stock. I ordered both last night online and will see from their reply what the case may be. Maybe because they have an order, they will order in some 588s. %88s listed at $3.75 and the 618s were $2.75. I'll keep my fingers crossed.
 
As I suspected, Mat electronics sent me the 618s but not the 588s. No word on the back order. We'll see. I'm a patient person and luckily I have lots of other audio toys to play with. I'll post again when I know more.
 
OK, I was PM'd on this, as I lurk the pioneer forum and had missed this...

First the specs with respect to previous work:
the sa-8500ii uses 2sb617, 2sd587 100/120v 6A 70W 7MHz 40Hfe, the amp is rated at 60 watts per channel
the sa-9500ii uses 2sb618, 2sd588 120/150v 7A 80W 6MHz 40Hfe, the amp is rated at 80 watts per channel

I used the ONSEMI mje15032, mje15033 ( 250/250v 8A 50W 30MHz 10-70Hfe) on an sa-8500II in this thread about replacing those transistors http://audiokarma.org/forums/showthread.php?t=98733
The amp used a total of four outputs per channel, so I figured that the wattage difference versus the total rated output power of the amp was not a problem.


oldtubes used the ONSEMI MJW0281A/MJW0302A ( 260/260v 15A 150W 30MHz 40-150Hfe) on HIS sa-8500II in this thread about replacing those transistors http://audiokarma.org/forums/showthread.php?t=72950
The transistors he used were massively overrated, but that's NOT a problem. They didn't fit as neatly in, but it wasn't mine, and I was going for a neater solution.

SO: you can use either solution, and as for the fabrication question, EchoWars DID make the suggestion of using the metal parts of the dead 2sxxxx transistors (or the whole darn thing...) as the hold down. Then you just need to figure out how to get the collector connections made.

One trick of fabrication is to use a hand drill and drill your first hole in about the correct location on the hold down bar, then screw the dead transistor in place on the hold down bar and use IT as a template to accurately locate the second hole. Drilling and tapping the optional third hole isn't that critical, a ring terminal under one of the hold down screws could do, I just didn't want to subject the collector lead of the replacement transistor to ANY stress.

BTW I used 1/8 thick aluminum about 1/2 inch wide and 1.1 inches long.
Other than the two holes, nothing is very critical.
The screws I used were M3 x .5 , 30mm long Pan Head Philips Machine Screws, you COULD get by with 25's but 20's were too short, and there IS clearance in the back of the transistor socket on the heat sink.

I may edit in more to this post..
 
Just for clarification, The replacement, which is rated at 220v and 50 watt, would be suitable for 120v 80 watt original? Would the lower wattage rating be increased due to the fact that my origin voltage is lower, as per Ohm's Law. I am assuming the wattage rating is how much this device would use at its max output. Are there any links that might help to educate me as to what the various ratings mean, amps, watts, mhz, HFE? Sorry about all the questions, but I am like a sponge trying to soak up all this info and I would like to order the parts so I can try to get my amp back to life. Thanks to all for the suggestions etc.
 
Ultimately the wattage rating is how fast heat can be conducted out of the transistor die itself, and how hot the die gets as opposed to how hot the transistor case gets.

The circuit of course may pump less energy through the transistor, with less wattage waste to be dissipated.

Calculating wasted watts to be dissipated isn't a trivial exercise...

60 versus 80 watts through 4 transistors capable of handling 50 watts apiece still seems to be enough of a safety margin.

Plus, looking at ONSEMI's lineup, they don't try to dissipate more than 50 watts with a to-220 package, instead the higher wattages are the TO-3 plastic package and the other mounting method.
 
It is now time to continue with this project and wondered if I could get some continuing input. Avionic is baby sitting me at the moment but if others have any input, I would surely welcome it.

I have chosen to go the markthefixer route using the onsemi mje15033 and the mje15032, using the little metal brackets that I have made up to hold the output in place. That part of it should work out well. I have the mica and the thermal paste and am ready to go except for the warning given to me by echowars is nagging at me. When the outputs were pulled, I cleared all the sockets to keep them from shorting anything and then I plugged up the amp and fired it up. It did not activate the relay and did not act like it fired up, but it did not blow anything either. I have tested all fuses and the diodes on the protection circuit and all is well there. I am now at a loss as to whether I should continue with the repair, or should I start tracing out potential problem areas.

Should the relay have kicked in? Does the amp need a load on it to kick in? Comments and thoughts welcome. Thanks.

Gary
 
This is a dumb question, but how did you arrange the collector connections from the transistor to the socket in back of the heatsink?

Wait, you fired up the amp without the outputs in place?

You need to read the dc at the outputs of each channel, with working driver transistors and NO LOAD, as while the emitter resisitors of the drivers are connected together, they are connected to the output through R28 a 2.7k ohm resistor. Temporarily reducing the resistance to zero may help balance the amplifier without the output transistors.
 
Mark, to answer your first question, I will jumper back from the collector to one of the mounting screws on the "markthefixer mounting plate". At this time they are just parts waiting to be installed.

I'm afraid I am not clear on your suggestion regarding each output. I see on the schematic where R28 attaches to the trace that makes contact with test points 3,6,9 and 12. Are you suggesting to temporarily install the outputs to do this DC check? Are the output transistors what you are referring to as driver transistors? You mention temporarily reducing the resistance to zero, does this imply removing R28 or replacing it with a jumper wire? Would you please clarify for me what you are suggesting, I'm sure it makes perfect sense but I don't understand what you are suggesting I do. Thanks for your assistance.

BTW I just replaced the main switch on indicator light. When I flip the switch the light comes on as it should. I don't know if it means anything but at least it works.:banana:

Gary
 
The suggestion referred to testing WITHOUT the output transistors in place, if the bias to the base is radically wrong, the outputs could be damaged, thus we try to achieve dc balance in the amp without the outputs and their large power capacity.

The base voltages when correct will be +0.6 volts and -0.6 volts.

The extra resistance of the 2.7k ohm R28 between the amplifier's output and the common point of the emitter resistors R14 & R15 (150 ohms each) of the driver transistors Q5 & Q6 will probably affect the ability of the circuit to balance under feedback, normally the balance point is the common point (amplifier output) between the emitter resistors (R16, R17, R18 & R19 ) of the output transistors (Q1, Q2, Q3 & Q4 ) instead, which provides the required feedback current . The resistor R28 allows an inbalance between the Q5 & Q6 driver transistors to less affect the balance the outputs are trying to achieve. Thus we short that particular resistor, R28 to establish that the new balance point which allows enough current drive for the feedback to work right.....

Q5 and Q6 are the drivers (they drive the output transistors) and Q1, Q2, Q3 & Q4 are the outputs.

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My little kenwood 3750 did this when i swapped caps i am sure it is the caps cos when my two fuses blow inside the amp this was due to caps wrong way around on the + -.
 
Transistor mounting

EchoWars said:
You won't find many (if any) substitutions for those transistors...not because their performance is anything odd, but their mounting is.
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This an old thread but jic anybody is searching this like I did. Here's how I mounted replacements for the "batwing" NEC TR's using the old TR's as hold downs:

Mntd2.jpg


Replacements in this application are MJE15033G+32G from Mouser. Cheap fix, sounds ok to me, we will see how it holds up. Used old insulator thing with no trimming, cleaned and new thermal paste Mounted w/soft zinc panhead#4 1/2" machine screws into the harder alum. heat sink.

sinkin.jpg
 
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