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

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This Kenwood KR-5010 showed up with a blown STK-0050 power pack that was causing a direct short in the receiver. I bought two things: the cheapest eBay replacement I could find, and the open source replacement made by an audiokarma member. Then I put each option "through its paces" and took note of what happened.
Link to open source STK-0050: audiokarma.org/forums/index.p...

[@n.shiina8798]

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

[@geomorphdog]

I second this. And you'll likely see the difference change as you change the volume.

[@dirkg3343]

To overcome the pot mismatch, set the volume to maximum and control the signal level via the output control of your signal generator.

[@Jim.D]

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.

[@jeremiahchamberlin4499]

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.

[@timcorner2821]

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.

[@JonPaul]

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.

[@ElectoneGuy]

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

[@diogenescaruaru]

Me too. I wish he could share the name of the ebay vendor so we can get those as well

[@Cass48]

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

[@frankscarano4708]

Pyramid audio has a far easier discreet solution that fits directly in place of the STK0050 packs with no assembly and is extremely stable. Its only two semiconductor devices ( dual darlington devices with a few SMD devices soldered to the board.. easy peasy.. I have used them before with excellent results!

[@terrym1065]

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.

[@richardmarshall6751]

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"!

[@Silent-Lucidity]

Very informative! Well done!

[@reinkansman1081]

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

[@mikecampbell5856]

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

[@b.powell3480]

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 !

[@TheBudliner]

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 😊

[@danielknepper6884]

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

[@PoppinWheeliez]

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

[@MyLittleBitOfEverything]

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.

[@rlgrlg-oh6cc]

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.

[@rlgrlg-oh6cc]

Actually, driving the module into hard clipping is not the worst case in terms of power dissipation. In that case, the transistors do not have much voltage across them at the signal extremes, so the power dissipation is low, since it's current times voltage. The worst case output transistor power dissipation is at something like 1/3 to 1/2 power. Probably it depends on the amplifier.

[@martyh9309]

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

[@fernarias]

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

[@josephlalock8378]

yup. it's for thermal tracking

[@dtracy03ss]

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

[@compass504]

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

[@1sostatic]

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.

[@danhorton6182]

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.

[@AHFixIt]

Yes, that is a mistake I made that I forgot to point out in the video.

[@rebootedelectronics]

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.

[@BStrapper]

Hi, did you buy all the (cheap) stk 005 from the same source? if not which source is the good one?

[@rebootedelectronics]

@@BStrapper Mostly from the same vendor, but I have about 3 that I watch for when I'm hunting for an STK. SemitronUS, Dalbani, and DoralElectronics all have good customer service. Even if the replacement is bad, they're quick to reply to messages and get things taken care of.

[@BStrapper]

@@rebootedelectronics So it sounds like lotery... and it might not be a question of good or bad vendor but rather a matter of luck?

[@rebootedelectronics]

@@BStrapperYep. The vendor isn't making the STK's. They're just selling them. I don't think the cheap replacements are built as well as the originals, but I think they work well enough in theory. The problem is that the manufacturer isn't doing a very good job of checking their product before it goes out the door. Some of them work like they're supposed to and some just don't

[@BStrapper]

@@rebootedelectronics i suppose the better vendors know better than anyone who are the good manufacturers of stk's, the most important part of their job to sell quality components... so i figure that to buy a stk 005 the key thing is to find a good vendor... or one of the very best.

[@chanoble3112]

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

[@martyh9309]

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?

[@John-N-541-ym7dx]

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

[@ingenfestbrems]

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

[@diogenescaruaru]

Yeah. Besides, that scale is far from accurate from what we can see

[@jimthvac100]

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

[@user-cd8ri1mc6s]

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

[@puciohenzap891]

Well, it's not like they haven't been running for 40+ years already ;-)

[@michaelakins6729]

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!

[@AHFixIt]

The eBay one after shipping from China was $10. All the components from Mouser and the boards from JLCPCB, I bought enough for 10 units and I already had some parts. Probably came out to about $12/unit. Then they took a long time to assemble, and it took awhile to engineer a mounting solution.

[@user-xm6qb5cg4i]

Hybrid IC is hell,

[@josephvarju1229]

Or the volume pot is a little off

[@josephvarju1229]

Yes the pot

[@idiamin6311]

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

[@BStrapper]

Hello how many did you buy from it-Ttronics? was it enough to be confident about the quality?

[@TSilva01]

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