Scott LK-60b Stereo Amplifier Repair and Alignment

A very interesting integrated amplifier with some unique features, including built-in test equipment to help with alignment! This was sold in kit form and the person who built this one did a very good job with the assembly.

[@Silent-Lucidity]

"Some of you like chasing electrons through a schematic!" That cracked me up!

[@TheTrueVoiceOfReason]

Happy 2023 Tony. I love these old amps. They just have a personality that today's amps are lacking.

[@kgsalvage6306]

That initial test function using a dim bulb is very cool!

[@isoguy.]

What a great amplifier that is pretty much fully documented and explained by our very own amp aficionado. I would buy an amp like this but I guess these days most companies don't want you to know how to fix your own kit, they just want you to throw it away and buy a new one. How these companies have the nerve to say they are customer focused and environmentally friendly I don't know. Have you ever thought of a retirement business for yourself, building and documenting an amp, tuner etc. using crowd funding? Backer number one waiting here. Thanks for this educational vid that I, and I'm sure many others have really enjoyed. Thank you

[@douglashoff95]

Those "Callins" capacitors and the "dome top" transistors-which I noticed one of on the phono board, have caused problems in units I have serviced over the years. The lamp idea was similarly built into the Knight Kit KG870 in which lamps were incorporated as emitter resistors for the output transistors as well. I do remember the advertisement for this kit when it was brand new in High Fidelity magazine, and remember "the only piece of test equipment you'll need is a 15 watt light bulb".

[@poormanselectronicsbench2021]

Looking inside as you did, the routing of wiring was not as "sharp" looking as the assembly manual shows it can be ( available at the "HiFi Engine" website), so ,there was some "that'll do" in the assembly. The "steady state" output is rated @ 40W RMS, both channels driven, it would have been interesting to see if it could meet specs still. I also wonder, if that difference of "balance" in your initial checks with the internal meter, and the difference in output gain, were fixed after you readjusting the bias and balance. Thanks for the look inside of it!

[@wimletzer4193]

Thanks for another clarifying video. I studied electronics in the 1980-ish. But I moved to IC development with philips. Now I am retired and love retrocomputing, building tube ampifiers and restoring old electronics.

[@kgsalvage6306]

Don't you just love working on these vintage amps. For me, tube is a little more interesting than solid state, but still great. The quality of workmanship was so much better than modern. Happy New Year!

[@johnsonrobinsonjr1272]

I love these types of videos with the attention to detail! Thanks bud!

[@2packs4sure]

My next door neighbor gave me one of those when I was a kid around 1977. I just called him, he is 88 and remembers it well,, he built it.. One of the channels crapped out in the early eighties and I just threw it away.. I'd like to have a do-over on that one...

[@markbryant4641]

Bummer!!

[@2packs4sure]

@@markbryant4641 Yep,, never dreamed back then it would be a classic. Before that I threw away a Fisher 800B with a channel out... Ohhhhhh,, man !!! Where's that time machine ?? lol

[@markbryant4641]

@@2packs4sure . Haha! I lent a friend of mine a technics 1200 mark 1. He was between turntables. It was cutting out in one channel so he took it to a technician and had the tonearm rewired and an ortofon blue cart installed. I can't ask for it back now he's spent a few hundred dollars on it. Oh well.

[@2packs4sure]

@@markbryant4641 Lol, yeah that's a dicey one,, in 5 years your friend could easily remember it as a gift and not a lend.. Ask me how I know..

[@markbryant4641]

@@2packs4sure please go on. I laughed when my mate told me about the repairs he'd had done to the Technics. He said it was the best table he'd heard. I shook his hand and said 'It's yours.' This guy has been extremely generous to me over the years. It's nice to think that he's using this table literally every day.

[@nickyace]

I remember .as a kid, my Dad had the same amp with an AR turntable and a pair of AR Speakers that I could rattle the windows in the house with. Great video!

[@retro_tech]

Wat a great amp. And what an incredibly well designed kit! I would have loved to assemble one of these. Amazing video and explanation too. I just discovered your channel and I instantly subscribed. Awesome content!

[@martyh9309]

Hello Tony. Loving the channel.and your content. My only comment is that I would replace all the remaining electrolytics and really check any film/paper caps left. IMHO....

[@mikepxg6406]

Great Job Tony. Interesting Amplifier. I Remember building My first amplifier in 1982 it was a Stan Curtis DIY design called a System A Amplifier published here in the UK in an electronics magazine called Electronics Digest. Stan Curtis went on to design for Rotel, Mission, Cyrus, Moth, Cambridge Audio, Quad and B&W.

[@zopilotesky3014]

I've always been curious about these kit amps. The single rail design is interesting. Thanks for sharing!

[@rankenfile]

Nice! The cap wizard tool was quite handy for this evaluation. Wonderful to see the outputs balance when you bridged with a good cap. What a nice kit with such useful instructions.

[@EsotericArctos]

One thing to remember with the cap tester is that it measures ESR, so if a cap is shorted, or has some kind of parrallel resistance, then it will likely still show good. It is a good tool to have, within it's limitiations :)

[@radio-ged4626]

"Poor mans Wheatstone Bridge" 🤣🤣🤣

[@gearheadted9210]

Old is gold,Happy New Year Tony,really appreciate you sharing your knowledge for greenhorns like me!

[@R.AudioElectronics]

Happy New Year Tony! This was a great amp with its unique features for you to illustrate some basic amplifier design characteristics. Great job as per usual Tony. I enjoyed the refresher

[@midmodaudio6576]

Thank you for another extremely well presented and informative video. I learn so much from your channel. I will be restoring my LK-60B (and LK-60) in the near future and will use your video as a reference.

[@benlopez4788]

This was a great vid. Very nice lil amp. Wondering in the output ballance evened out after the adjustments were made to offset and bias. Thanks for another great vid

[@robfors]

Excellent video as always! Thank you for bringing these to everyone! Happy New Year!

[@peterlarkin762]

Nice, another hifi repair channel!! Those big filter and output capacitors can be tricky... They may measure ok, and still leak electrolytic or have voltage loss. I've been working on an old germanium radio that has the same black plastic Callins capacitors. They're ALL bad! This was a shame, the capacitors were made in Shannon, Ireland, Near where I live.

[@zambrano966]

Como siempre Tony, excelente. Como dices tu, todos los amplificadores deberían tener un sistema así para ajustarlos. muy buen video.

[@garygranato9164]

happy new year tony, +1 biult in dim bulb test is a great idea

[@marka1986]

This is good design especially with negative feedback loop. It looks like there is a complete dc return path. Some amps required a speaker or load to be hooked up otherwise it upset the bias of the first transistor and sent you in circles troubleshooting

[@jasonmcintosh8212]

Happy new year and keep the videos coming. I respect your thoughts and knowledge and your time you put in videos.

[@andymouse]

" That's textbook 'shot noise !'.........I think..." Lol !....cheers and a great new year.

[@2aprotectsallothers592]

Thanks for all the knowledge that you share so unselfishly. Happy New Year my friend

[@craigm.9070]

Thank you for the very interesting journey through this amplifier. It is still amazing to me that such a great kit was available way back when for "Joe Hobbyist" to build. Just like you mentioned, this amp was not designed for large listening areas; homes and apartments were smaller on average vs. 2022/3. Is this amp headed for your personal collection?

[@justme_2020]

@xraytonyb - I hope you can get your hands on a few old vacuum tube stereo receivers some day. There must be plenty of them out there in need of repair and testing. Some of them really were great. I recapped an old Fisher stereo receiver that a friend gave me about 10 years ago and got it sounding great again. He liked it so much that he bought it back from me. I went through your entire "electronics 101-1/2" series. Great job with both the teaching and the successful improvements to that little budget tube amplifier. I did post a question for you about the "magic eye" tubes in other vacuum tube amp that you built, which I might try myself. - Vacuum Tube Push-Pull Amplifier Kit - Part 1 - If you have a moment, please look back to my comment and question there yesterday.

[@xraytonyb]

Magic eye tubes are just for "eye candy" and are not necessary. You can just omit them if you desire. As for the Tube receivers, I've done quite a few on this channel including several Fisher, Eico, Marantz (10b), McIntosh (MR Tuner) and Scott amps/receivers/tuners.

[@audiovideonut9078]

Hi Tony great bud as usual! I’m working on a 260 may I ask where you got those speaker cap adapters from? Thanks

[@frankreiserm.s.8039]

I am a fifty four year old electronics technician and I remember HEATHKIT kits. I remember when you could go to Radio Shack and buy electronic components. I also remember when toy stores sold models that you could glue together. I do not know why our society has lost an interest in electronic and kit building. Elenco also sold nice kits, but now they just sell stupid snap-on circuits for children. Gone are the good ol' days.

[@markbryant4641]

Hi Frank. Electronic kits for hobbyists are still readily available. For instance you can still buy Dynaco-Dynakit amplifier kits directly from Dynaco, USA. A friend of mine just last week bought and built a guitar effect pedal he'd purchased from an electronic parts store. And the plastic model industry is alive and very strong. Have a look here on youtube and you'll see many channels dedicated to model cars, airplanes, boats & ships...

[@frankreiserm.s.8039]

@@markbryant4641 You are smart. Are you an electrical engineer?

[@markbryant4641]

@@frankreiserm.s.8039 .No. I'm not even a hobbyist. I've repaired amplifiers and turntables. And guitars. Washing machines and dishwashers. But only out of interest and/or frugality. I used to LOVE making model airplanes when I was a kid in the 80s.

[@frankreiserm.s.8039]

@@markbryant4641 Okay. I have a diploma in electronics from National Radio Institute besides college degrees. I think that most kids today just like to play video games.

[@jeffreyhaynes5774]

Life with out Radio Shack stores is not good.

[@alex1520]

Great Scott!!!

[@kevinbeckenham3872]

I really enjoy your electronic repair lectures xraytonyb, you go into great detail that other people cannot be bothered.

[@philipblick8887]

Very nice informative video congratulations from Aotearoa (New Zealand)

[@fredfabris7187]

Hello Tony, I really have been enjoying your videos and am a big fan. Recently I was watching a video of your about the big marantz amplifier. In that video you spoke a bit about the imaging industry. I am very curious if I could speak yo you about the industry and how to get involved in it. Would love to get your contact info. Thanks, Fred

[@EsotericArctos]

This is a great video, but I do have something to say here. Having the unit on its side could affect the meter readings. The meter is designed to work in the horizontal position not vertical. Aside from that, this is a great video. Everything is explained well, and all the adjustments explained, just as you'd want it if you were building this as a kit. What an amazing amplifier. I wish they had kit amps like that now. We are missing out now. Young electronics enthusiasts have to rely on much less usefull kits these days.

[@pedrorm8632]

Felices fiestas y feliz 2023 tony.

[@curtc8389]

Excellent video

[@petertimp5416]

Thanks, another good job done.

[@bmboldt]

I was testing a receiver the other day with a dim bulb. With a 40 watt bulb or a 60 the bulb would stay bright and I was getting 4 V DC on my speakers. Without a speaker load the dim bulb worked fine. I had to put a 100 watt bulb in to get the receiver to work with a speaker load. For some reason the receiver couldn't start up with the smaller bulbs when the speakers were on.

[@theQdomain]

Great Video! Your Explanation of how the bias affects "crossover" distortion helps a lot. Just curious can the crossover distortion be seen on an oscilloscope? Thanks for sharing these videos. they are very entertaining and Instructive.

[@davet3804]

Yes ,a quick way to check amp is look for cross over distortion at low volume across a dummy load

[@theQdomain]

@@davet3804 Thanks. A good excuse for me to get a couple of high wattage resistors. I’ve been thinking about getting some for testing without fear of messing up my speakers 😀

[@davet3804]

😁the resistive load is easier to interpret than the inductive load from a speaker which varies with frequency. Use 1khz signal with low output and look for a notch as wave crosses zero point

[@marcodoria]

Happy new year Tony!

[@b.powell3480]

I still have the brochure for the whole line of H H Scott electronic equipment!!!

[@kenelsbernd276]

👍 Nice!

[@carlosgil4343]

How about installing a speaker protection relay when turning on? Do you recommend it for this kind of cap series amplifiers?

[@peterlarkin762]

It's always a good idea. Great peace of mind. However you will need a protect circuit specifically for single ended amp... There's an excellent discrete protect circuit on Rod Elliott's DIY hifi site, project 175. It will take high voltage. He makes PCBs too.

[@scrappy7571]

That's pretty neat with the built in dim bulb and the power meter. What did you do with the slight channel imbalance?

[@xraytonyb]

It was a bad capacitor on the tone board. I'm pretty sure I showed it in the video where I bridged a good capacitor across it and you could see the other channel come up even with the other on the oscilloscope.

[@scrappy7571]

@@xraytonyb ok,

[@ronwade2206]

Dad was the TV repair technician in northern AZ, then so was I, I fixed Pac Man etc. Art? 😅

[@t1d100]

Fantastic

[@Zonfeair]

Those adapta caps things where can I get them? Also do you have a video where you show taking out the boards and capping them then putting them back in? As someone new to this I really need to see how that is done professionally and how you keep track of where everything goes to put it back together correctly.

[@wolkewietje01]

I would also like a set of those. Normally I order different sized O-rings from Ali, but these PCB's also give the option to solder on extra binding posts.

[@dannyfreitas2120]

thats nice! amp

[@neccron9956]

Should you replace C206 & C205 with xy caps, and replace the power cord with a polarized cord, with the hot to the switch (even though the fuse would be on the neutral)?

[@xraytonyb]

Not necessary on this type of amp, as the power transformer provides electrical isolation of the mains leads.

[@Rastapapulus]

Can you plz share the schematic too? Tnx in advance.

[@erikdenhouter]

Bias is dependent of the mains voltage, there's no regulation in most amps, so (if I had a variac) I would first set the mains at the local voltage ? I never see some one do that.

[@marcodoria]

Hi. Most power amps don't use regulated power supplies in the output stages, so yes, everything's depending on the mains voltage. But when someone designs a circuit, provision must be made for such fluctuations. There are lots of service manuals out there that state, for instance, 10% variation on voltages on the schematics. I've never had a situation that called for such accuracy on bias settings. If it was to be that critical, the manufacturer would have specified a regulated power supply.

[@erikdenhouter]

@@marcodoria Well, I have a Marantz 1030 that needs 7.5mV bias, but it drifts 1mV from that for every 4V AC mains at 230V. But no manufacturer advising any variac setting says a lot maybe.

[@marcodoria]

@@erikdenhouter have you tried to check the minimum voltage required to bias the outputs, by measuring the emitter resistors? This may help to reduce the voltage and run you amp cooler. I think it will be less than what is stated on the service manual. Hope it helps!

[@erikdenhouter]

@@marcodoria Not sure if I understand you here. The 7.5 mV is measured over .5 Ohm. It is the only setting given by Marantz, beside an adjustment for symmetric clipping for pos. and neg. side of the sine wave. Btw, the amp is running OK, not warm at idle at all.

[@marcodoria]

@@erikdenhouter, don't know that particular model, and I didn't know where the measurement was taken. So no problem right? 😉

[@mackfisher4487]

Its to bad that today's Chinese engineering of cheap audio amplifiers couldn't adopt the Scott stereo amplifier kit philosophy. Produce a good entry-level amplifier kit design to teach basic skills as well as reward the builder with good sound. It would be interesting to find out if Scott made money on this offering.

[@jankowalski7211]

Subtitles please 🙏

[@jdmccorful]

Welcome to Tonys' School of S/S Amplifiers. Great education on this equipment. Happy New Year! Enjoyed watching and learning.