Restoring A Marantz 240 Power Amplifier

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The Marantz 240 and 250 can be a notoriously difficult amplifier to get right, but this one turned out great with just a few simple upgrades. The bias and DC offset came right into range and the sound is fantastic! The black anodized aluminum faceplate with silver lettering really makes this amp striking to look at.

[@historymakesmesleep]

HE'S BACK!!!

[@reinkansman1081]

Nice kick off to the latest series after the big move. Patience is certainly a virtue in your case. Love the cameos with Hodor and Sadie- you left them speechless.

[@Artofthesingle]

I had the same amp, black face and all, about 17 years ago. I had it repaired in NC. One side originally ran real hot. I held onto it for a fear years but eventually sold it. I had completely forgotten about it so thanks for the flashback.

[@JonPaul]

Wow, that's quite the task to get a 240\250 working properly. Myself and several people who are decent techs have failed on these units. There is a local vintage repair shop that will not work on these units. So you deserve credit for making it work and hopefully it lasts for years.

[@HAL4400]

I have repaired a few of these including 250M and 510(m), they are really not that difficult! the main failure points are the main transistors in combination with those old main buffers 63VDC20000MFD. These old capacitors ''pop'' when switched on. That ''pop'' damages the main outputs. however I must agree that these amplifiers are quite nervous! and those crap pots for the DC and bias don't help!

[@GraeboProductions]

It already worked before he took a screw out

[@mjg263]

Very nice thorough work! I see a lot of carbon comp resistors fail, drift or crack on older gear and they often get overlooked.

[@petercamacho1462]

Hay great job I was glad to see you were able to find the Marantz 240 amp I own one myself and added it Marantz 2265B plus Marantz 250 amp with Bose 901 speakers amazing sound quality I really enjoyed the videos you put out patients that you have really helps keep up the videos really educational

[@collinwood60]

Another interesting video Aiden. Happy to see you back to the bench making the HiFi repair vids. Keep them coming. Congrats on the move to Montana. One of the freest states in the country! You need to make Sadie the channel mascot!

[@carlosbarboni4374]

Hi, great job, those amplifiers are quite complex and hard to adjust when there is a problem. Right now I'm working with a 300DC and it has the same problem on one of the channels: the DC current went too far out of range. And seeing your work I'm going to check all the resistors that can fail. If you have any words of help or something else I can check I'd appreciate it. Thank you very much and keep going!

[@Itmonolith]

Nice job brother. I enjoy watching your videos and learning more about these older electronics. cheers

[@OpSic66]

I've ran across a few thermal compounds that were conductive. The worst part of any of them (aside from being conductive) is the contamination it can create in the solder joint, if someone is being that sloppy.

[@ericschleppegrell4467]

Nice work, sir! Those carbon comp resistors did their job for 50 years! Not bad for boomer tech! Cheers!

[@Silent-Lucidity]

Nice rebuild!

[@kellyrojo58]

Hello, I really enjoy your videos. Thanks

[@marcb8874]

Merci pour cette vidéo et cette explication, étant un petit bricoleur pouvez-vous me dire où le générateur de fréquence est connecté à l’ampli

[@ahelectronics5757]

Very good job !

[@pauldow1648]

Nice unit that kinda just fell into your lap.... 👍

[@len9518]

I think you should show some distortion readings, like tony does.

[@davedrew9328]

I cannot say I like the look of it ?

[@historymakesmesleep]

HODOR RULES

[@mirkovukoja233]

Niiiice job! Just put some more test music on. ;)

[@michellevey9608]

I admit that l did unsubscribe when you got into that engine swap thing. Maybe l'll resubscribe. Good video.

[@trevor245]

Great video but I am just wondering, is there a reason you do not use flux when soldering?

[@AHFixIt]

I use flux core solder

[@71organicmusic9]

👋 hi!!!!!!!!!!!!! Sadie 😊😊😊😊😊😊

[@jdmccorful]

Looks good! Thanks for your time.

[@gordthor5351]

I don't understand why so many people use a phone output to test sound quality. Phones put out about 500mv and have pathetic DACs. CD players and DACs put out 2 volts and have much better digital to analog conversion. Not to mention the analog output circuit. The difference in sound quality is night and day.

[@ewoutbuhler5217]

completely agree, line-out level is much better to test that headphone out.

[@davidsteinberg8024]

Also the impedances don't match as well.

[@terrym1065]

Good job Aidan👍👍 Taking the time to replace the resistors as well as the caps shows your patience and determination for results. House keeping the output transistors is mandatory I think, new compound = extended life. Yeah, nice work, thanks for the video. See ya soon.

[@mikecampbell5856]

I think xraytonyb said to plug the amp directly into an outlet while measuring bias, not the dim bulb. Great job at catching that.

[@erikdenhouter]

I just don't like switching a potential 240 Watt with such a relais.

[@mr.kenney536]

You do an excellent job of helping those with less knowledge to understand why you are doing what you are doing. You are constantly explaining what a color band means, how you know a particular resistor is of a certain kind (carbon composition), and the list goes on. I have bias pots on my Harman Kardon receivers that drive me crazy. I know it is because they are dirty but I have not quite dared to touch them up with Deoxit. I'm glad I didn't. You have a gift! Fantastic video.

[@bobbean4702]

Question: i have an old Fisher receiver with varactor tuning knobs (been sitting in the basement for 30 years) still works but all the controls are scratchy including volume. Would deoxit help?

[@BWBlues]

My 240 failed recently on one channel. The relay did not open and it put full rail voltage on one of my ESS monitor speakers toasting the woofer. Still trying to decide if I want to tackle the repair. So there it sits along with the 3800 preamp.

[@gordthor5351]

WTF? No power switch? Does Marantz expect you to pull the plug every time you want to turn it off?

[@ewoutbuhler5217]

nah, the pre-amp will have a switched power socket, most (pre-) amps and receivers those days had them. Saves you one or more switches when switching on your hifi-set.

[@gordthor5351]

@@ewoutbuhler5217 I know that era had switched plug, but many were only rated for about 100-300 watts. The inrush current (charging the large filter capacitors) on high powered amps can be much higher than what a low powered pre-amp switch can handle. Also, the vast majority of amps available are past that narrow era and do not have switched plugs on the back. It's more difficult to replace burnt switches that push two switches to turn on your system. Also it is better practice to turn on the preamp first and give it a couple seconds for the circuit to stabilize and then turn on the amp. It avoids weird spikes possibly harming the speakers.

[@ewoutbuhler5217]

@@gordthor5351 I don't really disagree with your technical reasoning, I was just stating the way it was back then. I'm sure the pre-amp that was designed to go with this amp has a beefy mains switch to allow switching on the power amp too. And relais timing of the power amp should be slower that the pre-amp, to prevent those horrible and possibly damaging switch on noises...

[@SheikhN-bible-syndrome]

Ive got several 100000uf 100v nichicon gold tone capacitors there huge 4.5lb each

[@ae4bp]

I just got a blackface 240. Do you have a BOM? Or, is it on AK?

[@stanleysullivan4257]

Are those Dynaco A-25 speaker on your test bench?I had a pr. of those back in 1975.

[@v12alpine]

Interesting that the right channel offset and bias changed with the line voltage but on the left channel they did not. Also the right channel offset control was so far off center. Something may be off or out of tolerance on the right channel, which shouldn't be too hard to track down with two identical channel boards to compare.

[@jimhines5145]

Great video. Good to have you back. How many hours would you guestimate you had in this project?

[@markusweissenbock6337]

SCHRACK relais - made in Austria!

[@Asian_Connection]

This is crazy good !!!! Thank you

[@minniekansman829]

Love your test music and the new workshop, good job!!!

[@thomasswenson5382]

On T03 transistors I use dry silicone insulators, no grease needed. The do cost more.

[@SteveMasonCanada]

Another great video. When you mentioned Deoxit possibly being bad for pots, I paused and Googled. Oh crap! Guess I'll stop that. Not that I've done many pots with it. Then I heard "I only have 1 meter" I had to stop and rewind. Does not compute! How can you only have 1 meter? 😀 And a quick question: Is there any reason you prefer Mouser over Digikey? Both are great, just curious.

[@AHFixIt]

I used mouser first. Both are indeed great, it all comes down to personal preference and who has what you need in stock.

[@SteveMasonCanada]

@@AHFixIt Cool. I use Digikey, as shipping to Canada is considerably better than Mouser.

[@ae4bp]

A Mouser BOM you used?

[@Lancaster_Hi-Fi]

Nice work! I always learn something from your vids.

[@mikepxg6406]

That is a beautiful piece of kit. Is that an LED Lamp ? You did a great job.

[@AHFixIt]

Nope! Just the original incandescent bulb. Thanks!

[@mikepxg6406]

@@AHFixIt Wow i’m A electrical engineer never seen a bulb like that apart from an LED Lamp, normally incandescent lamps are all glass. but if it works as a dim bulb….

[@scratchback2001]

I love the way you Americans say Dang or Dope. I live in Australia and I've seen one of these after a full restore. Unfortunately Marantz equipment took a China nose dive with their surround amplifiers. After a few months of use, the centre channel started playing up. I ran it in phantom mode but took it to a repair shop for a look. The amount of time he'd have to spend fixing it was a joke so I left it with him and went shopping for a new 7.1 amplifier. I was looking at some gear when I came across an Onkyo 7.1 unit. It was THX approved and ran all the audio matrixes I'd ever need and it was beautifully made. Point to Point wiring etc and the sound was phenominal. I remember Onkyo from the 70s when they made one of the first CD4 Discrete Quadrophonic stereo sound systems. Pink Floyd with a bit of the spliff was fun. (I'm 62 by the way) This new Onkyo unit is brilliant and by the time it's anywhere near clipping, you'd be bleeding out of your eyes and ears! The sub out is great. It only feeds the sub with relative info so the bottom end doesn't become overbearing. I've put a DBX 163 between the sub out and the sub to catch transients that can kill any speaker. So many things in Australia are no longer made here. Do you know that we don't even make a car here anymore? Australia made some beautiful Cleveland Earth tuners!! It's a joke. Anyway, Cheers from OZ, Andrew.

[@marcparsons1726]

You should pick up a fun inexpensive Superscope (R1240,1270). Would be cool to see a comparison. Fraction of the price of Marantz! I do have one and love it!!

[@magentaline]

Thanks! Love your videos.

[@AHFixIt]

Thank you!

[@johnmorgan6724]

Nice!

[@marcdich]

Very nice amplifier that you picked up. I have the goldish silver one with the meters. I’m not exactly sure what the model is because it’s late at night and it’s way across from me but I would say it’s probably early 70s and I paid up on that sucker I gave $1500 for it but I bought it from a Stereo shop over an hour away from me that goes through and does all these things so I won’t be reselling my amp anytime soon because I won’t get what I paid for it out of it Don’t it went wrong with it is they said they replaced pilot lamps but the pilot lamps burned out in it but I don’t care about the lamps. They did have a plate of the one you working on here on your bench, but it was silver, and they had wanted to die I think, either 800 or 1200 I don’t remember exactly which it’s been several weeks. I always bought it but I didn’t need it anyway.

[@Obsfucation]

If you’re going through the effort of making an adapter board for the relay why don’t you make it accept a relay socket instead and then you don’t have the problem of making it difficult for the next person who may have to change the relay again?

[@wayneg296]

👍👍😎✌️🤟

[@welderfixer]

That's one Heavenly amp. I wish could spend a day with it. Oh what a joy it would be.

[@GraeboProductions]

😢

[@paulmichaelfreedman8334]

My cat's the same... just wants three things. Love, food and sleep.

[@Andreas_Straub]

Really nice clean work. I was doing these kind of things 40 years ago, when the much better parts of today had not been available yet ... ;-)

[@aceautonewportky]

How could a person buy repaired vintage units? Again, as always thank you for your great content.

[@jakep8484]

Good vid, yeah I may check bias quick while on dim bulb but you need to set it when on the full wall voltage.

[@erikdenhouter]

If you can, check the bias at the right mains power. It will drift with that, so when your mains is low, the bias will be low. Not many people I watch made that connection, but the power supply is unregulated, so is dependant on mains voltage. When using the factory numbers I assume they calculate that drift in.

[@Dipurulez]

Amazing video…your videos helps me alot Thanks ❤

[@dexta32084]

I’m new to the channel but I must say is an amateur hi-fi tinkerer, his workarounds are greatly informative

[@michaelaue7411]

Do you think that the out put m volts different could be from the different output transistor

[@chucknanopoulos7227]

Good to see you back Hope the move went well Look forward to more stuff Thx again

[@Danteelias08]

hahahaha!.... i feel that when I hear that "buzz" sounded.... nice job at the end.

[@aarongunter5582]

I believe them amps was used in theaters back in the day they are rack mounted

[@justicelut]

Nice job mate, that's one gutsy amp!

[@alexzildjian]

Love This Vídeo , This Power AMP 😃💙👌

[@PsRohrbaugh]

Marantz ❤

[@collinwood60]

Thanks! Love your work Aiden. Dave D.

[@AHFixIt]

Thank you, Dave!

[@EddyTeetree]

Hi. Bought one of those a few years back. I think it’s a really good amp from when they only made good ones really. I used it with a vac valve preamp and phon stage. Very sweat and could crank too. Unfortunately mine went through record floods here and needs a replacement transformer as worms got in and ate the old style cloth and oil plate separators so it shorts now. Everything else is fine. The filter caps were original and also tested well. Would you know anyone with a transformer to sell. The original manuf. doesn’t have one. Thanks. I'lll watch this with interest.👍

[@AHFixIt]

eBay

[@matthewmahaffey2322]

Hey bud great content What area are you in

[@slpcorner]

Inspiring video - keep up the good work

[@MJLUCEY-sd1mq]

Have one of those. Bought it new. Doesn't work. Silver name plate, too.

[@ewoutbuhler5217]

now you know how to repair 😁😁

[@nonquit]

Nice + clean job, cheers

[@dougg1075]

That’s a tasty little amp.

[@revoxjazz8317]

Nice! Keep up you good work!

[@Keepee66]

Excellent job.

[@robertgriffin7569]

Good job, good to see you back.

[@brucetungsten5714]

Great job!

[@br.9055]

We love to see it

[@genehammond7239]

👍👍

[@handsomemann1]

What model is that Sansui you displayed for testing the Marantz? Curious to know.

[@AHFixIt]

AU-6600

[@handsomemann1]

@@AHFixIt Nice model.

[@zulumax1]

@@AHFixIt I have the AU-7700 and have owned it since it was just a few years old. I had been listening to a friend's Marantz 4300 here at my house for a week since I put in a new power switch for him. Now that it is gone the Sansui sounds meh. Maybe it is time for a restoration. I would like to see a restoration of your AU-6600, that would be sweet.

[@partylee007]

That is a weird but wonderful amp. I’ll bet it sounds awesome too now that you have restored it. Great video

[@GTI1dasOriginal]

... weird? It's an icon. The very foundation of the marantz brand. This "weird" amp was considered a benchmark and in some way, it still is.

[@partylee007]

@@GTI1dasOriginal still weird but also pretty wonderful

[@mariuszzzz]

Hmmmm... cut speaker cables usually indicate theft... Are you sure this amp comes from legit source 🙂?

[@mikepxg6406]

I doubt it easier to cut than fumble with a screwdriver just your paranoia :)

[@trevor245]

In what universe is this true lol, who steal an amp like this, in what setting....

[@EddyTeetree]

It usually idicates that the item is faulty. The power cord is quite often cut too.

[@karldettling5981]

Adcom 535 model amps have to be the finest constructed units in the world. And they are quite powerful to as they say they put out over the rated 60 watts per channel at 8 ohms. Some say up to 90 watts.

[@gettingoldsuckss]

Stuff over there, that stuff appears to be the emitter resistors for the outputs.