Which STK-0050 Is Best STK-0050? I Don't Know! 

the output difference between channels is usually caused by the volume pot. most standard multi channel pot were not matched to each other. i've seen 10% difference before. also, the small center transistor on your replacement retrofit unit supposed to be touching the heatsink. it is a thermal tracking transistor. if it's not attached to the final stage heatsink, you could get into thermal runaway if the final stage got hot enough

Enjoyed the video, thanks. BUT, really enjoyed seeing my old receiver being used again, it was my favorites back in the early 80’s when I bought one new.

A good quality pin-prick punch is a very helpful tool. A former Navy machinist mate turned me on to it. The pilot drill bit doesn’t need any more than the ‘prick’ to get started.

Totally agree on the idea that if you're going to have hot outputs then it's good to have a hot heatsink as that demonstrates the thermal transfer. I do sometimes compare the temp of the transistor case to the temp of the heatsink - if they aren't terribly far apart, that's another good sign of thermal transfer.

I have two of the audio karma packs in an SX780 and they work awesome.

Interesting how your having a different experience than me with the modules. I had them installed on my Pioneer SX-780, and there was no power loss and sound was no question better than before. My STK-0050's were still working and also had some capacitors replaced in audio path.

I'm surprised that fake Darlington pack performed so well.

Your efforts thus far have proven worthwhile, the greater the challenge the greater the reward. You've put in more work, on this receiver, than I figured you would so why not continue on eh.. I'm sure with some clean up and further troubleshooting the wave forms will come into sync. Maybe we'll see in the next video. (I think you need to build yourself a workbench turntable, would sure help working on stuff). Thanks Aidan for the work on and off the bench👍👍 See ya soon.

Very informative! Well done!

Nice video, thanks for sharing. I find it interesting that younger folks, like yourself, are comfortable building kits from just a BOM. I'm an old Boomer, and kits to me always came with a schematic, so that I could troubleshoot it when it inevitably didn't work initially. This kit is fairly simple, but I see folks making ARP 2600 synth kits with just a PC board and a BOM. That would never work if I tried it, I need a schematic, an interconnect diagram, and parts layout artwork. That is a "kit"!

Nice to get confirmation on your E Bay value buy. Nice scientific experiment

Channel tracking could be a function of mismatched volume pots....

Q5 which is BD1391 needs to be mounted on the heatsink.

Seems like every receiver that I've ever owned that had stk's in it, the bass was muddy.

Having a little blob so to speak, in regards to the heat sink compound is conducive to keeping the compound moist over time. It helps it to last longer and not dry out. So a little extra squishing out on the sides is not a bad thing 😊

I wish this was available about 20 years ago, so that I could have replaced the output modules on my Kenwood KA9600 receiver that took a power surge during a thunderstorm !

The mismatch in levels between the channels is not unusual. It's because the volume control sections don't track perfectly over the entire adjustment range. This is why higher end equipment often uses rotary switches with many resistors to get perfect channel tracking.

This would be a great application of trimmed capaitor leads saved for a future occasion.

Nice to see a basic comparison. Until you get into very expensive versions, most dual gang potentiometers used for volume controls will often have some variances between left and right along their range. Especially well worn ones. Usually only visible on a scope but not enough to hear.

"See if it explodes or something". I actually did laugh out loud, and you know I did because I spelled it out.

Hope you get the Pre amp figured out , Static and Tuner issue, but is pretty interesting especially at home, with the Flu! I'm having a Eleven series 3 gone through as we speak, hope it was better condition, LOL

Great vid.. how about adding a real small and quite fan blowing down the heatsink? Did the other modules get that hot?

Very cool video, thank you for sharing. I’ve built four pair of these modules, all for the SX-780. I see that you used the Toshiba outputs, I used Onsemi NJW0281 and NJW0302 outputs, but when completed I was getting about 60w per channel into 8 ohms before seeing any clipping on the waveform. Not sure what’s up with yours, maybe in that unit it’s causing the power supply to sag more??? One thing to note, I’m not sure how hot it gets or if it’s a sensor, but the TO126 transistor in the middle of the board is mounted to the heatsink when assembled as intended. That’s why there is a hole in the board at that point, so you can drive a screw through the transistor into the heatsink.

Most of those darlington STK's are pretty simple, easy to recreate with discrete components. It's the more complex Technics one's that get a bit hairy.

You're doing great with the tools you have! I think the biggest differences between the cheap STK and the open source one is quality control. I've purchased several cheap ones that were DOA or otherwise faulty and some that worked flawlessly. As for the max output differences between the two STK's, remember that there is a third variable that has to be met: total harmonic distortion (THD). It's quite possible that the cheap STK can put out more watts, but may also have way more distortion, even at lower amplitudes. That being said, equipment that can measure THD isn't cheap and checking clipping is still a good idea.

You need to scope the outer pins on volume pot and then the middle pins to check for balance..

When you did the last adjustments you were on the dim bulb. Were you on the dim bulb during the final power measurements as well?

Or the volume pot is a little off

I wonder if there are other stk replacements besides the STK-0050

Interesting that the custom replacement modules were less powerful than the original STK modules.

2:28 sure it’s not 2-3grams of contact sement on the heavier one?

Yes the pot

Hybrid IC is hell,

I find these videos very helpful, especially the troubleshooting. Can you give us a price comparison of what you paid to make up the custom STK replacement boards vs. what you paid for the STK pack on EBAY? Keep up with the terrific videos. Thank you!

Best STK is the conversion board to discrete transistors you did. STK means Short To Kill, or Soon To Kaboom.

Hello i am from switzterland . i buy all Vintage-STK by IT-Tronics in Germany.....100% funktional and very good qualitiy . Besten Dank und liebe Grüsse....Steve

Best STK-00xx is to reverse engineering the Darlington pack with modern transistors