Kenwood KA-501 Amp Antics 

The "Kessel run" You crack me up! Thanks for the humor and the memories....

Oh boy, I had a Pioneer receiver with one channel that changed when tapping the relais. I cleaned it like 3 tilmes throughout the years because it would come back. Now finally 25 years later I cleaned it once again, and put it back together. No change! It turned out one of the cables behind the relais wasn't soldered in properly from factory 😅

I'm here for crabby knowledge!

Thanks for this Tony. I have a couple of receivers that have channels only slightly mismatched but you've inspired me to get them closer to one other. Love the VAC measurement for troubleshooting.

Happy Holidays to you and yours Tony! Thanks for all you do to educate us.

One of the coolest electronic channels, he needs more subscribers .

I love these terse DRAGNET (...just the facts man...) videos with attitude. Short, sweet and lots of intuitive troubleshooting with just basic equipment. Very Well Done. 😊 (ps. The early "KT" Kenwood units from '70-71 are easy to work on. They used removable bottom panels back then...)

I bought one of these amps. I think it was in the 80's. There was a "slewing distortion" mania going around at the time and this was one that had high ratings in the Hi Fi magazines. It was noticeably lower distortion than my older amp. I used it for several years with complete satisfaction. One day I found a stand alone phono preamp for a bargain price and it followed me home. I connected it to the aux input on the KA amp and put on a Grateful Dead LP. It sounded pretty good, so I cranked up the volume and went to the frig for a cold one. Suddenly the sound became distorted. Then it became VERY distorted. Before I could reach the power switch the smoke came out. The output transistors were discolored from heat, and the driver boards had parts burned off and lying in the bottom of the chassis. The big caps were oozing fluid and the fuse was fine. Wow. I looked at the output of the new preamp and found a 12 MHz oscillation on the music peaks. This was unlikely to affect slower amps but the Kenwood -- tried -- to follow the input. It also dumped the DC offset into one of my speakers, burning the voice coil. Still no blown fuses.

left channel stubistor was not on heat sink tony . not picking we have all done it on accident. excellent video as always thanks for taking us on the journey i always learn something.

I always pick up a few tips...no matter what you are working on it's a good watch !

Hi Tony, I'm enjoying your mischievous humour in this one :-) At 16'30 approx, there are two 8A fuses in shot - the one on the right looks to have a much heavier gauge wire than the other one, worth a check.

Great fun, thanks for sharing.

The brand doesn't matter to me, it's all about learning diagnostic procedures & techniques. Like they say, more than one way to skin a cat.

I’ve been watching a bunch of curve tracer videos past two weeks and this video really shows why they come in handy. I love your video of the one you built, a real one is expensive to buy but a good diy is nice to have on the bench. I’m gonna rewatch your diy one again and see if parts are still available

Never use a big word where a diminutive one will suffice. Lol. You are an excellent technician, you have a great sense of humor and you should ignore any negativity in the comments on YOUR channel. Kudos!

Excellent troubleshooting video. Thanks Tony.

I must say, that full wvae bridge rectifier is rather interesting

Great video, merci for your presentation and explanation, very useful.

Wow, I learned a lot with just the Multimeter technique!

I love the look of it. I just acquired a KA-5700 for $15 that is in perfect cosmetic condition. The reported issue is that it keeps blowing fuses. Can’t wait to work on it. 😊

That was entertaining, Tony. I appreciate you even doing that video and putting it out. I remember those damn plastic snap standoffs. 🤮

Interesting fault due to the speaker relay! You nailed it as usual!

It looks like you forgot to reattach the thermal tracking thermister to the left channel heat sink.

Hi! Do you know (or does one of your faithful viewers know) where I can find the schematics to a Quadraflex 979 stereo receiver system? I have a bad channel on one side. Thanks for all your help and for these great videos!

i love big knobs

For some, it’s all about “some antics”.

only a true star wars fan would know that quote :)

Great troubleshooting! It’s always a bit more challenging when more than one variable is causing issues. If someone does not have a curve tracer and they suspect a pair of transistors being mismatched under load conditions like this they could potentially swap L/R transistors and see if the gain difference switches channels as an alternate diagnostic procedure.

6:55 I Have delt with those type selector switches a lot. They appeard in Kenwood, and Radio-Shack equipment of that era. And were all marked with Panasonic (Matsushita) partnumbers and logos.

I just had a pair of Kenwood KA-6100 and KT-6500 amp and tuner in here. All they needed were lamps and to clean all the controls. The units were clean but the controls were a mess. I had to clean and re-clean to get it all straightened out. Bias and DC Offset were good. Sounded really good as well. The controls were the bugaboos here.

Impressive troubleshooting.👍

Had to show me the badass curve tracer. Running out of room over here!

Happy holidays, Tony.

Tony, are saying electrical equipment need to be plugged into the electric outlets to work? NO WAY 🤣🤣

Repair interruption in low voltage AC power supply. I have used that on an invoice before, more than once.

Is it possible the solder joints on the relay were the cause? The contacts did not look like they should have been the problem.

0:23 - I'm guessing 'high speed' means high slew-rate!

I have the same, as kind i connect them as a car amplifier and connected a set of "sub woofers" as one speaker parallel over the right and left channel. It still works, but on a or b there is noise and overall the amp kicks in a little later than the relay. there is some weird transistors in there, you probably can't buy.

amazing stuff !

I spotted the problem, the pilot (boris the spider) is dead.

Regarding complainants who may feel that assailing your high-quality videos, covering multiple subjects in the field of tube and transistor amplifier repair, available completely free of any charge: I would like to suggest to them that if they're not satisfied with this treasure trove of generosity- previously unavailable anywhere, in any form- then they should perhaps go find some source which demands less of their attention and more of their money.

Very interesting and some great lessons. It would be great if you could have a project to make a home brew curve tracer. Y

Hi Tony, another interesting troubleshooting journey. Would you mind sharing with us what made you think it can be that relay you've already inspected? :) Thanks!

Had a similar problem with a NAD L54 receiver. Distortion due to bad relay contacts.

18:56 - ALL THAT for adjusting 3 or 4 resistances! :)

Ha-chachacha! I finished watching a vid on a Kenwood KA5002 earlier from VintageAudioAddict. Talk about co-inkydinkies.

Love it !

Interesting regarding the difference in transistors under load. Just found something similar in a Nakamichi pre-amp I'm working on where two transistors tested okay power off (diode check), but under load had quite different voltages. Quick question: these transistors were in a muting circuit (2SC1636) and have very high hfe (800ish). Is there a reason why muting circuits require that sort of amplification? Anyway, as always, enjoy the detective work 🙂

What about bad relay solders ?

hi - thks for the detailed video - do you know the volts and mamps of the vu meters bulbs please - thanks

Resistance, thy name is Futile.

it must be kenwood week. i'm just finishing up a kenwood integrated and have another coming up right behind it

Maybe they referred to the high slew rate.

You can use the tip of a bic pen, or any pen, to compress those pesky standoffs. You might need to cut it a little to fit the specific part.

Nice amp. Is it OK to have no speakers hooked up when turn it on? I was always told to have load on it when turning it on

What feature of the amp makes it "high speed" in the circuitry?

Too much of the old Eggnog there Tony

I'm trying to find a way to copyright the 1khz sine wave.' To me, once someone has an audience larger than, say, 10, one owes it to them to do the best one can with the language. Many grammar blunders can cause confusion or glitches in understanding. It should be worth the effort to avoid these issues.

Interesting: I'd never seen the innards of a KA-501 or any of that Kenwood generation. They sure cheapened the design. If you go back even one generation, Kenwoods are very different, and much better, inside.

I got this amp in my collection. I am not impressed with the building quality. Too much plastic parts for my taste. Like that thing connecting the rod to that switch in the back. It is prone to breaking. Also the knobs and flip swiches are rather flimsy. Overall the case looks rather 'empty' compared to my other amps.

You mean "Needs to be cleaned". You said "needs cleaned" You seem like an intelligent guy so I'm sure you know the proper sentence structure. It seems that this loss of prepositions is an internet thing where one person starts doing something and then everyone follows.

Kenwoods are not worth saving generally speaking.

Good stuff! Thanks for the look and your time.