HH Scott 460A amplifier repair (after the bath).

[@rossthompson1635]

One of the best explanations of a bias circuit I have heard. Really enjoyed your logical journey to find the faults.

[@electronicsoldandnew]

Glad to hear it.

[@DavidTipton101]

Thanks for another fine and well explained project Manuel. Transistor equipment is not something I know a lot about so your explanation adds another piece to my transistor puzzle. Cheers!

[@electronicsoldandnew]

My pleasure. Just be aware that I don’t always get it right :)

[@p4spooky]

The fix along with the detailed circuit theory/walk through is fantastic.

[@electronicsoldandnew]

Thank you

[@videotutorialegratis6232]

you explain nicely like at school. good materials you prepare. be patient.

[@electronicsoldandnew]

👍

[@electronicsoldandnew]

👍

[@GeorgeChristofi]

A brilliant bit of fault finding for sure. A lot of people don't understand the need for matched transistors but when you are dealing with higher end kit it needs to be done right.

[@electronicsoldandnew]

True

[@matele901]

More than troubleshooting and fault finding....A great tutorial. Thank you. The sought after HH Scott solid state amps are the A436 followed by the A457. The 460A and the 480A were made in Japan, the built quality was questionable. I bought a 480A in near mint condition and noticed that the STV diodes had their wires in place but not soldered to the pcb; the TO220 devices were not insulated. Surprisingly, the amp worked fine.I'll fix the odds. Sound-wise I still prefer the A436 for its "tubey" sound.

[@electronicsoldandnew]

Amazing that thing worked at all.

[@fredfabris7187]

Thanks for the video.... one of your best! I really enjoyed the step by step diag with the theory. I learned a lot!

[@electronicsoldandnew]

My pleasure

[@JacGoudsmit]

Great video! Awesome explanation of that current source and limiter circuit. By the way, I think XRayTonyB recently also repaired an amplifier that had a problem in its limiter circuits. The schematic looked very similar to the one in your video: Differential pair, two transistors, feeding into two Darlingtons with four limiter transistors.

[@electronicsoldandnew]

Thanks. I must go back a have a look at xraytonyb’s one to refresh ideas.

[@PeterMilanovski]

Great job, slow and steady wins the race! It's a beautiful amplifier and I'm sure that is going to sound just as good as it looks. All that is now needed is a pair of vintage three way 15" speakers to take advantage of that amplifiers output and you will be in audio heaven!

[@electronicsoldandnew]

I’ll keep praying, and maybe a pair of those speakers will come my way soon :)

[@PeterMilanovski]

@@electronicsoldandnew The reason why I suggested to use larger speakers is because they are able to reproduce the low frequencies more efficiently at lower output levels, it's not always about high output levels. I had a pair of Technics speakers that were a two way system, they had an 8" bass driver and a basic 2" cone speaker as a tweeter, before I even listened to them, I decided to upgrade the speakers with new and higher power drivers. I made the mistake of connecting them and I got to hear what they sounded like! I still have the speakers and the new drivers are still waiting to be used lol. The original design was extremely efficient and the bass response was surprisingly good, back then... They knew how to get the most out of a system.. The young generation these days will take one look at the motor assembly of the woofer and automatically think that it's rubbish! They don't understand that it was designed for a purpose, maybe not their purpose but one that is beyond their understanding... I watched a video where this guy was comparing the speakers that his company was selling to a range of other speakers that were not even designed to be used in a car! One of the speakers looked like it came out of one of those PA speakers that were used in schools, they had them here in Australia and I have even seen them in the US also, it has an 8" dual cone speaker that would have been transformer coupled to a 100V line.. It's a very good and efficient speaker for that purpose, I'm sure that if it was installed in a proper enclosure and connected to an amplifier with enough power to drive it, it would sound amazing for the full range driver that it is.. The guy who did the video found himself having to defend himself in the comments section, he was just trying to make a point but he didn't realize that people would see that he wasn't comparing oranges with oranges... I guess that's why it's important to have channels like yours, someone has to educate the masses LOL. You are master and sensei at the moment! Now I have to go and finish painting the fence..... Stroke up..... Stroke down..... Up.... And down..

[@dl7majstefan753]

Very good explanation of the bias circuits!

[@electronicsoldandnew]

Thanks

[@ericstarr3591]

Brilliant! I love these old Scotts and this is my favorite amplifier. I have 2 of them. Thx for the interesting video.

[@electronicsoldandnew]

My pleasure

[@billquantrill4960]

Lit up thats a really attractive amp. In my opinion H.H. Scott ranked up there with Sherwood, Fisher and a few others in the 60's as far as desirability goes. Not on a level with MacIntosh, but still decent performance and quality. I'm not familiar with their solid-state offerings beyond the late 60's, I have a Stereomaster 342 on the shelves thats tired, but an interesting receiver considering its socketed components. Good video and humorous in episode 1.

[@electronicsoldandnew]

👍

[@curtisgriffin7924]

Very nice video. The abbreviation on the ST chart was for the manufacturer (Sakken I believe). Excellent bias description

[@electronicsoldandnew]

Thanks for that info. I had no idea.

[@isoguy.]

Amazing fix, you have the patience of a saint. Would, if you have the time love to see the final item up and working even if it's a short unedited update. Thank you for sharing 👍👍👍👍👍 ⭐⭐⭐⭐⭐

[@electronicsoldandnew]

I’m going to do just that as soon as parts arrive and I’ve had time to complete the job.

[@isoguy.]

@@electronicsoldandnew thank you.

[@mackfisher4487]

Mr. Caldeira, Let me complement you on your approach to teaching, You logical troubleshooting process starting at the power supply working toward the front end is excellent that coupled with the computerized schematics troubleshooting using multiple colors to explain signal path is excellent and your unique to your channel (how are you producing a large soft copies of the radio schematics?). I hate looking at paper copies or small soft copies that I need a magnifying glass to read, it slows me down. It’s nice to see a technician sorry engineer, trace out a circuit using an ohmmeter before applying power then a voltmeter to finish ringing out circuit. Your injection of low-voltage AC into Transformers was a trick that I’m going to plagiarize. Your electronic knowledge in both solid-state and tubes sorry valves is excellent thanks for sharing.

[@electronicsoldandnew]

Thanks you for your kind words. I have described the software tracing in a video, linked below. It certainly makes life a lot easier. kzbin.info/www/bejne/pXvXh5ygm8hketU

[@Michlag]

Great job as usual, Mr. Caldeira... Now please a video on how to add an ir remote volume control to these amplifiers... Can't just stand up every time I need to pump up my marantz... Thanks!

[@electronicsoldandnew]

I don’t know about you, but that’s about the only exercise I get :)

[@Michlag]

@@electronicsoldandnew for me as well... But yet... ;)

[@saarike]

Great repair with much interesting information! Thanks a lot.

[@electronicsoldandnew]

Thank you

[@DavidBerquist334]

Do you use a isolation transformer 120 volt in 120 volts out i think some techniton s use veriac to bring voltage up to 120 volts slowly

[@electronicsoldandnew]

I use an isolation transformer, but in my case it’s 240 in 240 out. I’m in portugal.

[@weedonman]

Great video with detailed explanation.... thank you

[@electronicsoldandnew]

my pleasure.

[@bixy9347]

😎Cool looking amp

[@borayurt66]

I watch your videos as I watch action movies. I would love to be your apprentice if I lived anywhere near Madeira...

[@electronicsoldandnew]

Madeira always welcomes visitors from abroad :)

[@borayurt66]

@@electronicsoldandnew I really have that in mind. I have a dear friend that lives in Faro, who has been inviting me to visit for ages. If I do that, I believe it will be very easy to come there and visit you for a beer (on me) :-)

[@angelazura]

I have the same receiver. When I turn it on it clicks in and out of Protection until it slows down and eventually stops and stays on. Do you think it could be the same issue as yours?

[@electronicsoldandnew]

Could be, but it’s hard to say from a distance.

[@jeditoto3441]

I would suspect the power transistors

[@psionl0]

If I am reading that circuit diagram correctly, R29 is common to both halves of the protection circuitry and its value determines when clipping occurs. An incorrect value for this resistor would explain the symmetry in the premature clipping. Did that resistor test ok? Maybe a smaller value?

[@electronicsoldandnew]

You’re absolutely right. I’m going to revisit this amp when the ordered components arrive, and I think I’ll have to experiment with this limiting circuit. Much is still unclear and I think another gremlin is still hanging around. Thanks.

[@eduardoreyes221]

Great video man!! a lot info to learn from you, thanks a lot!. I have a question, i hope you can help me. I have a scott 440a and when i turn it on and off a "pop" sound on the speakers. Dont know it suppose to do that. I download the service manual, and i look the "Relay protection Circuit" description. What can be wrong to that pop sound when i turn the amp on and off?? Thanks!

[@electronicsoldandnew]

The pop should be completely suppressed by the relay on the output. If you have a pop on start-up, the relay protection circuit may be at at fault. The relay may actually be stuck.

[@eduardoreyes221]

@@electronicsoldandnew thanks!

[@mattw.3084]

My tech repairer was shocked when I told him about this video. Do you know where I can source a replacement vu meter as mine has stopped moving. There's none on ebay unfortunately.

[@electronicsoldandnew]

Afraid not.

[@mattw.3084]

@@electronicsoldandnew yes I thought it would be a tough fix. They weren't even commercially released in Australia as mine was imported from America so I don't like my chances of finding one for parts.

[@y_x2]

On the schematic C45 is backward?

[@electronicsoldandnew]

It certainly looks t

[@audiomuseumjoaquinhoracio8229]

Te felicito. sos un genio !!

[@electronicsoldandnew]

😊

[@DerekHerbst747]

Looking good. I've been persuaded that transistors are not forever. They get old and stupid like the rest of us...

[@electronicsoldandnew]

Yep. Can't get around the problems of age.

[@DavidBerquist334]

Realy - wash it wont that ruin caps corode switchs damage meters dosnt it say do not expose this product to moisture

[@electronicsoldandnew]

That’s what I thought, but no, it’s working just fine after all this time. wishing it out with alcohol afterwards helps.