Good afternoon, I am writing to inquire about something specific. I have a Technics SU-7200 to which the power transistors have been changed, and that ones are now short-circuited. Could someone advise me on whether using the original 2SD526-Y and 2SB596-Y matched transistors would make the amplifier work perfectly, or if there are other transistors that might work better? I'm not an electronics expert, but I have some knowledge. I would be very grateful for your help as a humble radio enthusiast. Thanks in advance.
Short answer is "no".
There is a technical problem in your amplifier and most probably replacing only the output transitors (for originals, if you can get them) will not solve your problem.
The answer to that question lies in the definition of "better". Old gear was designed in their days, there is not much sense in trying to "improve" them by replacing single components. You can find many more modern amplifiers that perform "better" in one way or another.
So my answer would be "use original replacements to keep the original character. If necessary, use substitutes to make the device work again".
The real sound quality problems with old gear are not in the output transistors but in the whole signal path - switches, lytics etc.
It will likely perform better with the originals, but they are not especially rugged against abuse. Obviously, neither were the replacements. True originals are unobtainium, but for the time being the Fairchild (KSB/D) versions are still in stock at Digikey. They are on last time buy status, so if you are a shop who prides yourself on using originals where possible, buy a couple dozen before they are gone. I run into them often enough in my travels where I’d use them eventually.
TIP41/2C will likely work but you’re not going to get Y grade hFE. At least not in the NPN, the PNP often does go that high. Whether or not this matters depends on the circuit, and how picky you (or a customer) is. They will be at as rugged, but probably not much more. If you are trying to burnout-proof it I’d go to the 2N6488 (BD911) series. Big as they go for TO-220. The problem with that is that it might necessitate driver upgrades. To put it back where it’s supposed to be without needing to reverse engineer, id hurry up and grab a couple pair of KSD526/B596.
As tempting as D44/D45 are for performance reasons , they do not have the SOA, and one shorted speaker wire and you’re right back here with shorted transistors again.
TIP41/2C will likely work but you’re not going to get Y grade hFE. At least not in the NPN, the PNP often does go that high. Whether or not this matters depends on the circuit, and how picky you (or a customer) is. They will be at as rugged, but probably not much more. If you are trying to burnout-proof it I’d go to the 2N6488 (BD911) series. Big as they go for TO-220. The problem with that is that it might necessitate driver upgrades. To put it back where it’s supposed to be without needing to reverse engineer, id hurry up and grab a couple pair of KSD526/B596.
As tempting as D44/D45 are for performance reasons , they do not have the SOA, and one shorted speaker wire and you’re right back here with shorted transistors again.
Hello, I apologize for taking so long to respond to your posts. I greatly appreciate your recommendations and analysis of the matter at hand. Well, it's clear to me now; I will get the original transistors. I've seen them on eBay, and as they should be, matched. It will be more convenient to buy them already matched than to buy a dozen and match them myself. As soon as I have the amp repaired, I will let you know how it turned out. Thank you for your contributions; they were very helpful. Good afternoon.
Original Toshiba are completely unobtainable, and anyone selling them would be suspect until TESTED. Fairchild (now part of ON) made good copies of a lot of original Jap parts (at their Korea fab) but now many of them are either extinct or on their way out. Nobody builds discrete power amps this low anymore - they are all chip amps these days, so demand just isn’t there. Digikey has these particular ones for now, but they have been EOL’ed. Once stock is gone they’re gone. Then you really will be stuck with low gain substitutes.
Good evening, the transistors finally arrived. I bought a total of 4 pairs from different suppliers. However, I have a question; one of the pairs, the D526-Y, is from Fairchild Semiconductor, and the B596-Y is from Toshiba. I'm unsure if this could be an issue. The other two pairs are both from Toshiba, but the B596 is labeled as B596-O. Does this pose any problem? Could someone please clarify these doubts for me? I'm not an expert. Thank you in advance for your input. Good evening.
Fairchild’s made-in-Korea KS copies of original Japanese (2S) parts are good. No issues at all. The only issue with Toshiba is they are NLA and you’re subject to getting fakes if you get them from anywhere as new. I trust pulls a whole hell of a lot more - because at least at one time they were working. The Fairchild version is soon to be NLA too - so when they’re gone from Digikey they will be subject to the same skepticism.
O vs. Y is just the beta grade. Statistically, the Y batches are higher gain. At this power level, the circuit would have to be pretty screwy not to work with either. NPN and PNP never match perfectly, because the gain profiles vs. collector current aren’t the same anyway.
One would wonder that there is any profit in faking parts like these but apparently there is.
O vs. Y is just the beta grade. Statistically, the Y batches are higher gain. At this power level, the circuit would have to be pretty screwy not to work with either. NPN and PNP never match perfectly, because the gain profiles vs. collector current aren’t the same anyway.
One would wonder that there is any profit in faking parts like these but apparently there is.
It will probably work fine forever as long as you don’t go cranking low impedance loads. That type of transistor in general is good for +/-28 volt rails at 8 ohms only, and that’s where I‘ve often seen them run. For 4 ohms I’ve run them on +/-18 (25.2VCT Radio Shack transformer) and they were fine. But I wouldn’t push it further.