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Great work as always James! The new rack is looking sweet too. How are you liking the sound compared to your Yamaha gear?

Great work Nigel, nice attention to detail on the rear panel and delrin feet too.:music:

Some seriously high quality work there by rottalpha. The best of past and present combined.

The -25 refers to the gain (hFE / beta) gain grade of the transistor, in this case 160-400 according to your data above. Also note that the BC327 has a different pin-out to the 2SA950 (the latter has a center collector). Unless the transistors have failed I would advise leaving them alone, just...

Just for another data point, 128kΩ in one of my units (a little tanned already): I like these too, also thanks to Nashou for the tip on adding description to mouser orders.

Could be unrelated but it's worth rebuilding the small power supply above the front transformer before troubleshooting (if you haven't already), the last one I worked on had major glue corrosion and cracked joints there.

Reasons are: The B-2 benefits from a small increase in filter capacitance (improved bass response). Modern production capacitors regularly fall in the lower end of the +/-20% tolerance (rarely +). More options available in 22000uF. Nichicon LKG in 63V or 80V are popular choices, both work fine...

In my experience different tweeter resistors can have audible impact due to inductance properties at high frequencies. There is some measurement and discussion on this topic here. Not all "non-inductive" resistors are created equal, the best ones will provide an actual datasheet measurement...

Close enough to call equal. After swapping outputs and setting the same initial bias, observe the driver IC temperature between the two channels. If you have an IR temp gun, post the left and right values at the driver IC heatsinks near cutout time. Another Sony amp with a similar circuitry...

Same 6mV creep and IC overheating on both channels? Do you still have one good pair of original outputs? If so, I'd try the original outputs on one channel and check if the problem goes away.

Guessing you mean CM6-S2. They are good speakers and can be used as stereo mains, the key to getting best performance from these is to find the matching B&W stands, fill them with something heavy (dried sand etc) and bolt them to the mounting holes on the base of each speaker. You can also make...

It would be interesting to see the THD and harmonic profile compared between the 2SK77 and 2SK180 (in your restored B-1s), particularly at lower output levels / realistic listening levels. No doubt you have already explored this. Thanks for sharing your R&D in this unique space, it's always a...

The B-3 service manual is a unicorn, even in Japan. If someone obtains it, it would be best to upload directly to hifiengine for everyone's benefit. I do have the schematics for driver boards, regulated PSU board, and muting/protection board - shared below: 30mV is a good starting point...

They are 50mm diameter and 80mm length from memory, with solder terminals but not the same as KGs. Whatever is used will likely need some modification to fit (eg. solder tabs attached if screw terminal caps are used). You'll also need to go up to 80V on the replacement, as 63V will be too low...

Try cleaning the normal/direct switch on the back also.

The collector current rating (Ic) is the difference. KSC1845 has Ic = 50mA max, which may not be a sufficient replacement for the 2SC536 (Ic = 100mA max) in some applications where the device is being operated at the upper end of its SOA. In many signal applications it will still work fine, but...

Side note - most mount these pots to the solder side of the board to allow adjustment without flipping up the board / stressing the wires. The reason is that they do not have secondary dial access on the underside of the pot (as the factory ones do).

Definitely cracked. Re-flow with soldering iron and add some solder (60/40 lead-based, or similar).

2SA912 and 2SC1885 are 150V / 50mA / 0.75W. For easily available parts, KSA1381 / KSC3503 are a much closer replacement than the KSA1013 / KSC2383 you tried previously. As a general rule, if your sub has an Ic order/s of magnitude higher than the original, it will have much higher Cob and...

Which model Sankens and from where? Can't buy semiconductors from China, almost guaranteed counterfeit. Chances are you replaced the failed parts correctly but the parts were not genuine and failed under load. If you list the original part numbers for both outputs and drivers we can recommend...

Confirm which components have actually failed first, did you try replacing the fuse with the correct rated part? The A-1020 doesn't have driver boards in the conventional (70s) sense, the output transistors are still soldered to the main board, so all you're doing by removing the "driver"...

Thanks Karl, great to see you're still around!

Excellent work! So the original C2704 is good on both channels and just D117 had failed? If the schematic is correct D117 is a 3.1V zener - if so, your multimeter wouldn't confirm correct operation. Might have been a damaged or failed part, if you have a zener capable tester you could check...

Would love to hear more of the Toshiba gear, they've made some of the best audio transistors in history. Aurex made some serious products. https://audio-heritage.jp/AUREX/amp/sc-lambda99.html I found some more photos of the SC-665 and SY-665:

The tester recommendation was just to avoid making pin-out mistakes (and bricking your amp), a cheap tool can only provide so much information. It won't show common failures with intermittent transistors, nor is it capable of testing to most in-circuit voltages let alone breakdown voltages. I...