Kenwood KA 9100 - Part 4

[@barryf5479]

I started out repairing TVs and stereos in my early years while going through engineering school. I must remark that you really "took this thing apart" and made a lot of repairs and necessary component replacement. I was amazed that it worked right away. I would have likely have made a couple of mistakes that would have given me grief. You did not. Your attention to detail and your patience really paid off. Great job!

[@jlev505]

I normally repair car audio amps and work on circuit boards for oilfield automation at work. Car audio stuff is what I do at home. The very first home amp I worked on was this exact same amp. Not fun recapping every single cap. This amp was definitely not service friendly. It wasn’t as bad as I thought but much worse than car audio amps and equalizers/ processors. I watched all 5 parts before I tore the old girl apart. The one I restored look like it was stored in mud in the bottom of a lake and had a wooden case around everything. Thank you for your videos. I started watching your videos several years ago when I got into electronics and didn’t know ohms law, or what a diode, transistor, cap or resistor was. Now it’s my 9-5 and what I do on the side at home. All my power supplies I bought as parts/repair. Now I have around 10 working Power Designs, HP, Trygon, Lambda, NJE and 2 Topwards. The old made in USA stuff is easily repairable and built like tanks. Thank you, Tony. I really appreciate all the time and effort you put in to teaching. It’s much appreciated!

[@nicodenhaak3961]

Great job Tony as always. There is a very simple way to remove the corrosive glue. Just use freezespray, and you can wipe it off with no problems. Even the glue which is still kind of flexible, just crumbles off. I do it this way in my shop. Good luck with the Kenwood, best regards from the Netherlands.

[@xraytonyb]

I've never tried that. Thank you! I guess I was on the right track, just the wrong direction. Cold instead of heat!

[@gregjohnson5194]

Just a fantastic rebuild series Tony you did a excellent job. Total quality!!! Love it thank you for sharing with us.

[@jdmccorful]

The value of the repairmans technique can never be overstated! Great session;especially the demonstrated cleaning and reassembly of log. pot. Thanks!!

[@seanobrien7169]

Dark side is the album i always do my listening test with. I have been listening to that album for 45 years now on any kind of system imaginable. I know that album like no other. Not saying it is the greatest album ever (though i could make a decent argument) but it is certainly the music i know best.

[@GeorgeEI7KO]

Nice work as always Tony. Can't beat dark side of the moon. One of my favourite albums. Regards from Ireland my friend.

[@JamesEscobar]

Wow beautiful job Tony!!

[@hestheMaster]

It's done. Well it was well worth it Tony. Thanks for showing it.

[@TriAmpMyFi]

That's a beauty......................................... 🔈🔉🔊

[@justinmijnbuis]

What an elegant and clever solution for the different sized capacitors, admire that one!

[@haqitman]

At the beginning of this series I thought it was a lost cause. I stand corrected. Nice work Tony!

[@Parkhill57]

From a pile of junk to a beautiful amplifier. It was enjoyable watching you rebuild it!

[@MrDoneboy]

Kenwood and Pioneer have rocked my world for many years, Tony. Thanks so much!

[@Enigma758]

Lovely restoration!

[@mdzacharias]

Regarding the volume pot: One can apply say one volt across both elements and view the DC outputs on a scope, and easily observe the volume tracking characteristics.

[@philipslighting8240]

What a top job real skill. I would be proud to own such a thing.

[@EdwardLehman]

Amazing display of patience and education, can't thank you enough Tony , for what you do for people who love vintage equipment. Bravo!

[@craigm.9070]

Simply an incredible resurrection of a great amplifier. I especially liked, "I'm going to make a change" on the soft start addition. Probably just a cost cutting measure to not include it in the initial design and production, sadly. Thank you again for your time Tony, really looking forward to the performance video.

[@stintus1]

I must say you do impressive work, and excellent tips

[@randyr.parker2698]

Turned out PERFECT! You do such a nice job getting this old (better than today's) electronics from the good old days working at better than factory specs! REALLY enjoyed that one. 🙂

[@jeremiahchamberlin4499]

Great work, Tony. You set a high standard for caring enough to do the job right the first time.

[@sguttag]

Nice job Tony. A couple of comments: 1) for finding a footprint, if you have a photocopier or even a flatbed scanner, it can be a fast/handy way of coming up with a footprint to start drilling things. If you go with the scanner/printer method, ensure that scaling is set to 100% or "actual." 2) On the soft-start, why bother with customizing it for each amp by choosing a high wattage resistor? Why not, instead, have a simple timing circuit for the relay that jumps out the NTC after a set time? One would still get the benefit of it resetting at each turn on and it would be universal for all amplifiers. You could deluxe it by having a VR to set the timing if you think some amps need just a bit longer of soft-start. 3) On the LEDs, you don't always need to make the power into DC. They're diodes, they'll do that naturally. So long as you don't notice/object to the flicker (60Hz isn't normally bad). They'll glow at ½ brightness. A key is to ensure that one does not exceed their reverse voltage. Often, a resistor is all that is needed.

[@xraytonyb]

Thank you for the comment! To answer your questions: 1) It was easier to just poke the cap leads through some card stock and cut it out than to go upstairs and use the scanner/printer. 2) The resistor for setting the trip point of the relay coil doesn't have to be high wattage, as it is only going to have about 10 milliamps passing through it. In addition, this circuit is simple and inexpensive (only 3 components) and has the added advantage of using the charge level of the capacitor bank to determine when the relay comes in. If the caps don't charge for some reason, the relay will never come in. 3) This will work, but I usually don't like using the LED as the rectifier. Quite often, these low-cost LED's don't like the reverse voltage on them. I suppose you could use a diode and resistor in series with the LED, but it was just as easy to make this little supply. I think either way will work fine. Thanks again!

[@sguttag]

@@xraytonyb thanks Tony. Great answers. I've been down these roads before, hence my comments. On the soft start, one can also have fun with zeners on it. Use a zener to clamp the relay voltage and on the voltage drop, one can use a zener to drop the rail voltage into a suitable range (zener in series). You do have fewer parts in your design. The zener approach does have the supply to the relay a bit more "regulated."

[@bobdoritique7347]

well done! Merci fot this series, very interresting.

[@stephensams709]

Very well done Tony : )

[@harlest71]

Great video Tony !!! I love your work.

[@mohammedajman3066]

Wowwww .... so professional work ... amazing

[@ElektrikaCo]

Every time Tony says pyramid, it reminds me of the Yamaha B-6 videos 😄

[@xraytonyb]

I still have nightmares.....

[@petertimp5416]

Good job…thanks Tony.

[@erikdenhouter]

PF, Us and them, don't want to leave that division on for to long... Little tip for LED replacements for some small bulbs: on the back of a 5mm LED you can just get 4x 1N4148 fitting in the circle, and no smoothing needed, only a dropper.

[@garygranato9164]

in video part 1 i really thought this amp needed to go to the junk bin, but i was wrong. good to see another classic amp resqued :)

[@vsalasarcr]

Hello, great to be able to learn more from you, thank you for all your time.

[@lanceromance6793]

Thanks for sharing your pot treatment. My kenwood amp needs cleaning periodically as it will start to cut out after some time. I've been using just some deoxit but your video shows an accurate condition.

[@hippydippy]

Fantastic Job! That amp deserved the love. Look forward to the last episode.

[@philipslighting8240]

Those Kemet Capacitors are excellent. Good job.

[@zambrano966]

Excelente trabajo Tony.

[@adalbertus777]

Great series of videos on this beautiful gear. Thanks Tony for sharing your skills, knowledge and passion with us. P.S. I think the front panel is flat again, isn't it?:)

[@xraytonyb]

Mostly. I couldn't get it perfectly flat, but it's much better than it was.

[@JayRCela]

Is always nice to watch one of your videos, I used to work in the HiFi industry late 70's until 1983, some of the Kenwood stuff was a great value for the money product line. I was very disappointed when they and a number of manufacturers started using the Darlington Power Pack chips for the output stage, I never felt that they sounded as good as some of the earlier products that used discrete output transistors, what is your opinion? I am leading up to this question regarding a recently acquired Sony STR-6800SD receiver that was stored in someones garage rafters for a really long time, it needs to be cleaned and looked at for a possible refurbish. I do remember these when it was a current model and they sounded excellent, a very smooth natural open spaciousness, so to get to the point I believe these also use a Darlington output configuration, regardless I would like to have a qualified tech look this over for an assessment. I found a reputable vintage audio repair shop in my general area and for $80.00 they will give me an estimate and complete documentation of what needs to be done. I feel this is more than a fair price to have an expert opinion, what I would like to ask you is, there must be a certain point in the cost of repairing this unit where you have to decide is it worth it? Thank you very much for your KZbin Channel, It is one of the best out there.

[@xraytonyb]

First of all, the $80 bench fee seems pretty fair to me, considering the cost of everything these days. As for the Darlington Power Pack modules, I've found that when they are used in a properly designed circuit, they really perform well. Because all the components are on the same substrate, they have very good thermal tracking and hardly ever suffer from bias creep. The Pioneer SX-780 was one of, if not the highest selling and most popular receivers Pioneer ever made and they used STK0050 modules running slightly under-powered (hence the 45 watt power rating of the receiver). There are still a ton of them out there and I would say the failure rate of the STK modules was on par with that of the discrete amps such as the SX-750. I own both and they are very similar in sound and performance.

[@g.fortin3228]

That's a keeper ! Great job. Love the mod! and very thoughtful to make it easily reversable, for the purists.

[@NICK-uy3nl]

Better than new - with soft-start, upgraded XFMR, modern PS caps and cool blue LEDs 👍👍👍

[@davorst699]

Friend that is doing restoration for he's entire life said that nitro thinner works wonders with glue in this vintage stuff. I'm using it and yes you need to be a bit patient when removing it but result is great. Just use cotton swabs for soaking glue and some plastic chisel tool(you can DIY it) for scarping it off. You will need to soak glue all the time during scraping it off. After you cleaned it just use isopropyl alcohol to clean PCB. And that slow start circuit is really great, simple and it won't break down, i used it around 15 years ago for first time.

[@mistermac56]

Nice work and great explanations on the work you are performing.

[@martyh9309]

I like the soft start idea and curcuit. But I would wire it into the AC supply side after the main fuse.

[@gregjohnson5194]

Pretty sure he did right? The only thing on the dc side was the coils to bypass the limit resister after capacitor charge up.

[@keybutnolock]

Nice ! Looking forward to hearing how it sounds. Mr. Wright would approve, I think. Thanks for sharing.

[@scrappy7571]

Awesome work Tony! Is the soft start board available, or is that something you had made?

[@mackfisher4487]

Extra points for using a two-prong polarized plug versus a three wire cord with the equipment ground pin. My experience is that having an extra equipment ground can introduce problems in equipment that wasn't designed for it. Particularly communications receivers that have three or 600 ohm antenna input where half of the antenna is at ground potential. (I/E ground loop issues) 31:00

[@apollorobb]

Mouser and Digikey have been horrible lately with stock and lead times They rarely have the caps i need and their transistor stock is bad too. Tried to order some KSA733C's and they dont have the C variant and i use a bunch of those as they have the Center Collector . Been hard lately to get Receivers Done with the parts issues

[@harlest71]

YES!! and what's up with Nichicon and all the End of Life caps. All I see is This product is no longer manufactured. Starting to worry a bit.

[@xraytonyb]

I sure hope this isn't the new normal. I agree. Mouser and Digikey are like Mother Hubbard's Cupboard.

[@scrappy7571]

@@harlest71 Yeah, alot of the audio caps are going obsolete. What are we going to use.

[@harlest71]

@@scrappy7571 I've been stocking up as much as I can but you can"t get everything. I'm hoping this is just a transition to different product lines but more than likely it's a push to get rid of vintage gear. Don't wait, get your favorite amplifier now and rebuild it.

[@apollorobb]

@@xraytonyb I have noticed as well a bunch of the jelly bean go to audio caps are being phase out going EOL this is concerning I love my KT's

[@grahamkent2868]

Great video, I have one of these amps and they sound magnificent, look foreward to seeing test results!

[@wedoshotz6645]

Outstanding work......again. I may try your soft start circuit on a friends KR unit that is prone to power switch failure.

[@mithunhaque]

For that dried old glu, small drop of kerosene over night is easiest and safest treatment I've ever experienced. You can try once for your own experience. . .

[@kenielsen]

I actually think I will try this simple soft-start to bypass the NTC...👌👍 -Maby a novice question: but can the connection of the relay coil directly to the PSU introduce more noise...?? Often a soft-start needs its own supply, hens my question

[@xraytonyb]

The relay coil acts as a resistor while it is energized and won't cause any interference. When the relay drops out, the back EMF will cause a short pulse, but it won't interfere with anything in this design.

[@TheJimmydan67]

awesome work sir

[@pa5ca]

Hi, Tony, brief question, why making the rectifier board for the meter backlighting LED's . The LED's are diodes and you could just run them from the AC voltage and add the resistors no cap need. Perhaps a 100nF decoupling cap's across the LED's. Yours, Frans

[@xraytonyb]

LED's don't like reverse voltage on them. You still need at least one blocking diode in series with it and the dropping resistor, but it could flicker when running at half-cycles like that. The capacitor would solve that. The bridge rectifier would also eliminate the flicker without the capacitor, so I could have left the cap out of the circuit.

[@__Dude_]

@@xraytonyb Tony, since you rewired the illumination anyway, why did you not attach to 30VDC? No additional rectifier and cap needed. And since there are two LEDs, instead of a blocking diode in series, the second LED copuld have been used as such. The remaining flicker would be insignificant.

[@IAWAF]

Tony, I was wondering if you have worked on super-expensive equipment such as Dan D’Augustino, Gryphon or Boulder? If yes, what are the differences in their construction to justify their tens of thousands of dollars price tags? Anyone can answer.

[@davet3804]

Nice job ! Pink Floyd ?

[@keybutnolock]

Us and them - darkside

[@gabidaniel5615]

How is the sound compared to pioneer sx 1250?witch one sound better ?

[@xraytonyb]

They both sound good in their own rite. The Pioneer has a lot more gas in the tank, but if you don't need to go that loud, both will do a good job.

[@hooters6951]

I recently brought out my Kenwood KA-9100 along with all my old stereo gear that I purchased in 1978. It powered right up but when I put an audio source into it I got no sound and no movement in the VU meters. Any ideas?

[@jlev505]

I would first check if you’re getting signal at the output/amp board. If you don’t have a signal, start from the jack and trace to where it stops.

[@benburkett6560]

hello mr tony. ive been watching you quietly for 2 years now. keep it up! question, i have a mac mc2100 do you have any boards left? ben burkett

[@xraytonyb]

No more 2100 boards. They pretty much sold out in the first 3 days. :(

[@bobikae]

Hello, please if the volume potentiometer for the Kenwood KA-9100, KA-9150 amplifier is in stock, I am interested. Thanks for every reply. Best regards.

[@ronbradshaw7404]

This amp is specked at 90 watts per channels, both channels driven and, it has been clocked at 120 watts/ channels often.

[@aransmitch]

in my opinion Repair work is not difficult. But it will be cumbersome to find replacement parts. how serious are you with matching transistors which affects the sound especially distortion.

[@2packs4sure]

Tony I would have gladly paid $300 for that minor tune up...

[@t1d100]

S-u-p-e-r!!! Thank you. I built a DIY Isolation Transformer out of two identical transformers, back-to-back. I only want to be able to supply 3 amps from them. However, when I turn them on, without a load, they pop a 3 amp slow-blow fuse. I have had to use a 6 amp slow-blow fuse, just to turn them on. Please point me to your video where you developed your soft-start unit. Please give me any tips for using it for my application... Particularly any math... I am using USA120VAC and 3 amps max. The Variac can go to 140VAC. My setup = Emergency Shutdown Switch to Isolation Transformer to Variable Autotransformer to Dim Bulbs to Load. Please and thank you. Edit: For clarity... The fuse is part of the Emergency Shutdown Switch. It pops when there is nothing connected but the Iso Transformer. Meaning, no Variac and no Dim Bulb and no Load. I watched your Soft-Start video. I think that I just need to develop a power supply for the relay... Diodes, or maybe a dropper cap...

[@benburkett6560]

Figures. Well mr Tony would you be willing to email me your final schematic and board layout? By the way, I’ve always wanted to ask you this, whats your favorite or best sounding amp and receiver that you have done? Thanks brother Ben Burkett Sv572b

[@hoobsgroove]

What's wrong with the main filter caps? Could you not have reform them?

[@philipslighting8240]

The only safe way to reform these is with a hammer.....

[@xraytonyb]

The ESR was still OK, but they were beginning to get leaky. I changed them out as a precaution.

[@hoobsgroove]

@@xraytonyb electrically leaky yeah ok. What made you choose that capacitor? There's lots of capacitors to choose from. Really split film is the best for power supply filtering caps. They have no EMI or infrared

[@philipslighting8240]

@@hoobsgroove It doesnt matter. Its an old amp......

[@jimomertz]

Why don’t you just get bulbs from superbrightleds? They have ones that work with AC from 12 to 120V, in all colors.

[@steverogers508]

All leds will operate with AC. Tony could have had a simpler panel lamp conversion using an appropriate resistor

[@RGD-Games]

i use a Dim bulb setup, when plugging in any unknown amplifier for first time, And after repairs etc.. I know how it works, and what its for... (bulb takes up the power in the event of a short)... But one thing that ive never known, is why a smaller wattage bulbs, limits the power to the amp.. that a large bulb does?!?! As you'd imagine... you'd assume a 100w bulb, would give the amp less power... than a 40w bulb would... Ive just never questioned it.. Ive just always had a selection of bulbs for testing amps.. 40, 60 and 100w.... ive just never understood, How a smaller bulb, Limits the power more...

[@jamiewykes8585]

Think of the incandescent light bulbs in a dim bulb set-up as power resistors that give off light, more light given off as the current passing through them goes up. A 100 watt bulb has a lower resistance than a 40 watt bulb. When used in a dim bulb set-up, these "power resistors" are in series with the equipment under test, so a lower series resistance (100w bulb) will limit the current less (allow more current into the load) than a higher series resistance (40w bulb). Think of the bulb wattage as an upper limit of the wattage that could go into a shorted load that is connected to the dim bulb at 120vac. I hope that makes sense.

[@pollycat1294]

who on earth turns on there high power amp with volume up! WTF?

[@xraytonyb]

You wouldn't believe......

[@IAWAF]

My habit is to always turn down the volume before shutting off equipment, including the car radio, so I don’t get blasted (and my speakers blasted) the next time I turn them on.

[@ronbradshaw7404]

I'd like you to xxxplain the "ground potential" on vintage audio and the twisting together of AC wiring importance?.

[@stevent3450]

Twisting is like a shield, its very common

[@xraytonyb]

The wires are twisted together so that the electromagnetic fields cancel out. The same technique is used in ethernet cables on computers.

[@TheBababa420]

Just a comment, because I know they count.