Marantz model 26 receiver: Almost done

[Alex_Baker]

Hello All

I just picked up a nice specimen of a Marantz model 26 stereo receiver for a good price since it needed work. I have already fixed what was wrong with it but I thought I would ask this question to some of the more experienced techs out there.

What I would like to know is if there are any capacitors that should be replaced due to their age, as this amplifier is bearing down on 50 years old. I will list the brands and types of caps in case anybody wants to know that.

-Nippon Chemi-con, Nichicon, and Elna : Aluminum Electrolytic  (I have always worked under the assumption that these are good brands).
-Mallory: Aluminum Electrolytic
-Matsushita (the triangle logo?): Aluminum electrolytic as well as some plastic purple ones labeled as electrolytic.
-Unknown brand : polyester type
-Unknown brand : Ceramic (I generally assume that these don't go bad)
-unknown brand : mylar type (the flat green ones)

I would love to hear you peoples opinions on cap brands and types, as well as my assumptions stated in parentheses. I know capacitors is a common topic so I hope I am not beating dead horse here, but hopefully I will learn something new!

The below pictures are of the various boards and should show all the different types of caps.

[bob91343]

If you insist on fixing what isn't broken, I would limit the shotgun replacement to the power supply filter capacitors.

If you get more ambitious than that, you risk making errors.

[David_AVD]

I agree. I've seen too many perfectly working vintage amplifiers mangled by bulk cap replacement.

Some had traces torn off while others had created dry joints all over the place.

Also, sometimes totally inappropriate replacements were used (low ESR or normal instead of low leakage).

All of this makes getting the unit working so much harder and time consuming than repairing any original faults.

Better to check for visible signs (corrosion / leakage) and maybe remove a couple of example types for testing first.

[floobydust]

I would replace all the small electrolytics. Why? I find the grey Elna electrolytic capacitors are pretty much end of life, they must be 45+ years old. They dry out and go low value, usually the small guys under ~220uF. Just test some to confirm.
What I do is make a spreadsheet with a list of the caps, for each board. Or, go to eBay and see the cap kits for the 26. Small 1uF and 2.2uF it's common to use Wima film caps instead. Pic related, that guy gives new small transistors as well. The loudspeaker protect relay usually has badly oxidized contacts and need cleaning without breaking it.
If you haven't done this before, or don't have a decent desoldering tool, patience and tenacity, then I would not do it.
Touch the dial cord with a soldering iron and it's destroyed. Forget a cap location or polarity, and screw up the board (hint: take lots of pictures). Clumsy soldering and you'll ruin the PC board.

I have a Marantz 2252b to recap, just haven't had the time and the dial lights are extra work.

[beatman]

just replace all caps with good quality brand same capacitance and when not found the same voltage you can do with bigger.16v can be on his position 25v.i do  a lot old complicated devices 25-35 years with succsess.just be very carefully when desolder don t made anny damage on traces and take care for the right polarity of the new caps.

[Alex_Baker]

Thanks for the feedback so far.

I understand the risks or firing the parts cannon, I have been guilty of that myself as I am sure everybody has. I was curious what experiences other people have had regarding recapping.

One of the inspirations for this topic is another Marantz AMP that I repaired a while back where two caps shorted in the preamp causing low volume. At the end of the day I replaced all of the same brand/type of cap, thinking that the others were not far behind. With this topic I was interested to see if anybody had any input on similar problems.

My ultimate intention is to sell the model 26, but I don't want to do that is there are caps that have a high chance of failure in the near future. I think I will sample some of the coupling caps for capacity and ESR, as well as check all the large filters, I will post an update on that hopefully later today.

[BrokenYugo]

I no longer find it easy to entertain a "recap", or "bulletproofing" of anything post vacuum tube unless it's showing trouble, revenue critical, or a known cascading failure point. I've done everything right one too many times only to have the thing quickly fail on me in some uneconomical to repair manner anyway, just with a bunch of time and money sunk in it instead of as found.

In this case I would think it comes down to the market. If these things sell higher recapped, high enough to cover your parts and labor costs of doing it right with good parts, I guess go ahead. If not, ship it.

[floobydust]

Vintage Marantz receivers and amplifiers etc. are commanding high price, so restoring them should be done with care and integrity. If it sells for $600+ who would leave in antique parts and assume age is the reason the bass isn't there. I recall they are "designed in USA" and Japanese manufactured, so some great metal work and looks, yet fairly straightforward designs.

It would be interesting to see the real cost of a re-cap/re-lamp. I'm usually on the phone with friends while doing it to save labour costs. Then I forget which cap I've just pulled lol.

[Alex_Baker]

I bought this amp for 100$, and did a 2$ repair on it to get it to where it is now, which is not too bad, and given that many model 26s are being listed by people in the US for at least $400 I feel that is is worth replacing at least some of the electrolytic caps.

With that being said, replacing all the electrolytics would cost only about 25$ shipped on Mouser. But here is where I may go down the rabbit hole a little, first question is are there any brand recommendations? $25 is probably the lower end on the cost of a cap set, but I chose a brand that was available(I have not bought these yet mind you). BTW has anybody heard of the brand "Wurth Elektronik"? I have but I don't know anything about them except that they are German and mouser has plenty of stock.

My next question is, and this may be dangerous , are there any other caps worth replacing for reliability and sound quality? I am not saying that I would replace them on this particular device, just curious to pick the brains of some people.

[rsjsouza]

As others have said, if you plan to sell it AND did not see a bad capacitor there AND does not see a price difference in recapped/original, I would leave it alone for maximum profit.

Obviously that, if you want to consider the fun factor in recapping AND have the experience and resources, go for it. All in all, you can never pay too much for improvement in repair experience.

Good luck with your decision. 

[Alex_Baker]

Thanks for your advice, I am at the stage where profit is not the end all be all. I am a hobbyist and an engineering student who likes to repair electronics while learning a few things, profit is just a nice bonus on top of the experience that I gain from working on something.

That aside I don't think it will be worth going after any other caps besides the electrolytics, they should be high quality and (hopefully) long lasting. If I had to replace any I think it would be the ones labeled as "poly" (polyester? polystyrene?) in the parts list, on the board they look like exposed rolls of foil and clear plastic of some sort, which just seems like it is waiting for moisture ingress to cause trouble.

[Alex_Baker]

Ok, a quick google shows that polystyrene caps are quite good and long life in the right conditions, I trust that Marantz knew what they were doing and I will not touch them. Should have googled first.

[rsjsouza]

Ok, a quick google shows that polystyrene caps are quite good and long life in the right conditions, I trust that Marantz knew what they were doing and I will not touch them. Should have googled first.

Precisely. Unless you see something really bad, leave them alone.

[slbender]

I don't think it will be worth going after any other caps besides the electrolytics, they should be high quality and (hopefully) long lasting. If I had to replace any I think it would be the ones labeled as "poly" (polyester? polystyrene?) in the parts list, on the board they look like exposed rolls of foil and clear plastic of some sort, which just seems like it is waiting for moisture ingress to cause trouble.

Each of those “exposed rolls of foil and clear plastic” parts are polystyrene caps, which are among the most prized, and most stable caps ever produced, often of close tolerance, high voltage rated, and could not be bettered, shy of some truly mega-buck caps - often twenty times their size, each likely costing more than a working Marantz 26 is worth.

Steven

[Alex_Baker]

OK, so all electrolytics have been replaced, no issues there, however there is quite a bit of idle hiss. I traced the source of the hiss by grounding the signal connections(on one channel) J406, J408, J412, and J414 until the hiss went away, which it did when I grounded J408. J408 goes to the tone control knobs, service manual attached below.

Does anybody have any input on this? there is also some 120Hz(line) hum, but I need to trace that more.

[Alex_Baker]

There is 14mV ripple on the 38V power rail, is that ok? I would like to see lower but I don't really know.

[james_s]

14mV is nothing, that wouldn't concern me at all. A properly designed amplifier is very tolerant of noise and variation on the supply rails. As for capacitors, aluminum electrolytic are the only kind I would consider replacing unless something is obviously wrong with one of the others. I have had to clean up too many devices where someone thought it was a good idea to replace all the capacitors wholesale and screwed it up. The most annoying was a case where someone asked me to re-cap an amplifier, I quoted him a price and then he decided to do it himself, screwed it up and then asked me to fix it for him. No thanks.

[Alex_Baker]

OK, thanks for the confirmation on the ripple. So I still need to find where the 120Hz hum is coming from, though I don't care about that as much as the hiss. I have attached some pictures of an audio spectrum app on my phone. The top picture is the noise floor in my work space(amp off), and the bottom pic is the amp on with nothing connected. I held the phone up to the speaker for the test.

Not sure if that provides any useful information, I though it might give an idea how loud the hiss is.

[andy3055]

If there is 120 Hz hum, look for bad screened leads on the signal paths. Often if a screen that is grounded comes loose, you will get hum. It could be a dry solder joint-considering the age.

Also take a good look at the power supply and make sure the ground/chassis connections are intact.

[Alex_Baker]

Everything regarding grounding looks good.

Curiously, if you look at the audio spectrum if when the amp was on, there is a peak at 180Hz according to the app, I wonder what that is...

[james_s]

Is the noise identical on both channels?

[Alex_Baker]

effectively it is, the left channel might have a tiny bit more hum that the other but it is barely noticeable.

[floobydust]

Where's the schematic for it? It could be many things, but I'd be measuring some voltages to see if anything is way off. It can "work" and pass audio even when a stage is starved for voltage, as well as cause PSU hum to get exaggerated. Or maybe it's just noisy due to design and grounding etc.
I thought the volume control was ahead of the tone-controls, leading into the power amps? That gives a poor S/N ratio. Placing the volume control ahead of the power amp section is for best S/N.

[Alex_Baker]

Sorry for the delay, I typed up a whole response for this and I don't know what happened to it. Service manual is attached below.

Currently I am doing some more testing to try and determine where the hum and hiss is coming from, I will post if I find anything useful.

Just for peace of mind, it is not likely for a recap to cause these two problems is it? provided everything was done correctly.

[james_s]

I think you forgot to attach the service manual.