I have a very old Sansui A-40 that has all the amp output and driver transistors blown (seems like a weak design) ... maybe more...replacements are hard to find and expensive. Do you think I should go through the trouble and expense to repair it or scrap it for parts. It has a nice transformer I could use but that is about it.
Many older amps/receivers can be made to work with modern easy to source transistors. Some lend themselves to improvement, others not so much. What kind of power supply voltage are you working with?
I have a couple old receivers that people gave me for free because they were blowen up. If you just replace parts with the same as the originals, you can expect it to last no longer than it did before. Most older amps could use some updating, especially wrt reliability. The most valuable part of an old receiver (etc.) is the chassis, heat sinks and transformer. But unless you need such a device, or know where you can sell it, maybe you should just trash it. Today the features of classic receivers are mostly obsolete. Or maybe you need a hobby, something to do? I am not about to create an account at hifiengine to look at your problem, so if you care, you should fetch the schematic and post it here in order to get better advice. If it's like what comes up on a search, it looks pretty typical and may not need much modifying, except maybe scrapping the phono input for Bluetooth.
It came up pretty quick for owner/repair manual
TO-220 output devices Sanken 2SC1827/2SA769 30 watt 100 volt
looks like 35 volt power rails.
I would assume just use typical MJE type
Original pair was 5 MHz and 10 MHz PNP was actually faster they put a cap over the NPN driver to likely stabilize it.
With moderns remove it. Cdom is 22p in original likely just raise it to 68p for moderns
Already a full unit in a case with working pre and case.
Very easy to repair simple power amp.
No need to use original replacements, plenty of modern transistors that drop right in with better specs.
likely the usual go to TO-220 On Semi MJE types MJE15030 (npn) 15031 (pnp)
50 watt transistor needs derating, far far better than 30 watt de rated originals
remove the 100p across the drivers C41 and C47
raise C33 / 34 are 22p raise them 68p
If second gain stage is bad 2SC1845 is sold by on semi as KSC1845
2690 and many others will work.
Drivers didnt look them up if TO-126 same old BD139/40 or MJE243/ 253 be fine at these voltages.
Original Outputs sucked and they compensated the drivers for a poor matched output with a 100p cap.
As noted remove it with a matched modern pair.
Amp is very simple easy repair, easy to substitute transistors.
It may be interesting, educational and fun to attempt a repair.
But how badly do you want what you'll end up with?
You could use the power supply, case, preamp... with any other amplifier you're interested in building.
It can be easier to work on an amp that's just a power stage on its own PCB on the bench, compared to working on a consumer product.
It might be good to understand why it blew up.
It's up to you.
I decided I have enough stereo integrated amps and started messing with some active crossover stuff, but I ran out of winter evenings.
But how badly do you want what you'll end up with?
You could use the power supply, case, preamp... with any other amplifier you're interested in building.
It can be easier to work on an amp that's just a power stage on its own PCB on the bench, compared to working on a consumer product.
It might be good to understand why it blew up.
It's up to you.
I decided I have enough stereo integrated amps and started messing with some active crossover stuff, but I ran out of winter evenings.
I would venture a guess as to why it blew up - using 4 ohm (or 2 pair of) speakers. Or shorted speaker wires. TO-220 outputs just aren’t strong enough for that. And Fairchild discontinued the FJP5200. If you want to use 4 ohm speakers with one of these amps, use 2N6490 or BD911. They are the only TO-220 series that will hold up on +/-35V and 4 ohms.
+/-35V on a single pair of TO-220 is silly, even if they are 90W devices. Almost reasonable on 2SC5200/2SA1943 provided they have good protection. As I said before, if you just replace devices, expect it last no longer than it did before. I lived through the time when this sort of thing was common because people making "solid state" amps did not understand SOA and silicon was expensive. One of the old amps I fixed by adding an additional set of 2N3773s driven by the original ~TO247 outputs, essentially in class-B. +/-35V on a pair of TO-220 might be OK in class-D.
Anatech would have my hide if I suggested retrofitting with 3P-N cased devices. But the last one like that I did got C5242/A1962’s. At the time they were the cheapest option (among real audio types). Somebody before me just put in TIP41/2, and they just failed again.
When keeping this type of amp original I used D525/B595 - the old Toshiba parts. Supposedly UTC is making them again (Fairchild/ON recently dropped them). When using them, it is with the admonition to heed the warning on the back that says “8 ohm minimum load”. Last amp I put them in had +/-25V rails, which is perfectly fine, with 8 ohms of course. I ran out of my stash not long ago, and OnSemi actually recommends 2N6491 as a replacement.
When keeping this type of amp original I used D525/B595 - the old Toshiba parts. Supposedly UTC is making them again (Fairchild/ON recently dropped them). When using them, it is with the admonition to heed the warning on the back that says “8 ohm minimum load”. Last amp I put them in had +/-25V rails, which is perfectly fine, with 8 ohms of course. I ran out of my stash not long ago, and OnSemi actually recommends 2N6491 as a replacement.