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Zenith MM2604-4

John Ragland

John Ragland

New Member
Just picked up this console, in really great shape, for $25. Turns on but all I get is loud buzzing/humming noises. Some volume control (buzzing gets louder)... I don't know anything about how to go about restoring this beauty. The interior is very clean and my suspicion is that all it needs is new tubes and maybe a turntable belt (there was some black debris underneath this area) and needle. And it's missing one of the brass louver pulls. Any/all advice re. next steps is much appreciated!

console.jpg model.jpg inside1.jpg inside2.jpg inside3.jpg turntable.jpg amp and tuner.jpgspeakers louver1.jpg speakers louver2.jpg
 
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First of all, if it's buzzing / humming, don't turn it on until the capacitors have been replaced. It almost certainly needs those (and in all likelihood does NOT need new tubes).

Your first step is going to be acquiring a schematic. Looks like you can get the Photofact for that chassis from Sam's:


Annoyingly, they also seem to have hits for "3L02" and "7L01" ... I guess those are the individual sub-assemblies for that model? (One for the power amp section, one for the pre-amp / tuner?) 7L01 seems to refer primarily to the AM/FM receiver from a cursory search of the interwebs.

Anyway, you can get the Sam's Photofact number from their web site and if you don't feel like spending the $ for the document, you might check to see if your local public library has them available.
 
Careful, that one's a hot chassis. All tubes run in series off of the main power. The hum would be 99.99 percent the electrolytic power filter capacitor. The tubes are usually not the culprit here.
 
Beitmans covered the 7L01, doesn't list the 3L02, but 3L01 or 3K02 is probably close. You can find them here http://techpreservation.com/schematics/Zenith.htm but you'll need the DjVu browser plug-in. There are other programs that can open DjVu files, but none of them will work... and at present, I don't seem to be able to open most files from this site. However, I do have the complete set of Beitmans on my hard drive, so I can provides them if all else fails.
 
cademan said:
Careful, that one's a hot chassis. All tubes run in series off of the main power. The hum would be 99.99 percent the electrolytic power filter capacitor. The tubes are usually not the culprit here.
Click to expand...

Can you explain what you mean by your "Careful" and "hot chassis" warning? If there's a shock risk, what's my next step after acquiring the schematic? Is this a DIY project for a newbie or do I need to get some expert help?
 
Hot chassis means that it has no power transformer and one side of the 120VAC mains is usually live on the chassis itself hence the term "hot chassis".

It is pretty easy to replace the capacitor(s) but these types of amps/receivers are never good candidates for stand alone service. It is best restored and kept in its original cabinet with all safety interlocks in place for normal use.

Series string means that the power runs through each of the tubes heaters (the part that lights up) and if one tube burns out, the whole thing goes dead. Just like those series string Christmas lights.

Read here:
https://en.wikipedia.org/wiki/All_American_Five

Even though yours is not one of these all American 5 radios, the amp and tuner in yours works the same way so be sure to take any and all necessary precautions when working on these outside of the cabinet or original enclosure.

As a newbie, and in case you are wondering, those two smaller transformers are the speaker output transformers are not related to a power transformer in any way.
 
OK, I shelled out the $22 for the Sam's schematic, which covers both the 7L01 tuner and the 3L02 amplifier. Had no plans to take anything out of the cabinet, if at all possible, but wondering now what the best plan is for buying a replacement "electrolytic power filter capacitor" (seems like the place to start based on earlier comments). And what about tubes, if that fails to fix anything? Where/how does one come by those? Tom Bavis was right, by the way -- I installed the DjVu plugin but still couldn't open their files...
 
I think the first thing to do is to get rid of the hum/buzz. The tubes are most likely ok and you can still get them on the internet somewhere. Take the amp out and turn it over and I or someone will show you which one is the power filter capacitor that needs replacing. Then you can replace others as needed but the loud buzz is going to be a bad power filter capacitor so you don't really need a schematic except for reference and troubleshooting in other places in the amp and tuner.

You can actually see the capacitor that needs replacing just below the 7695 tubes. The brownish orange-ish cylindrical looking thing hanging there. The voltages and specs are usually printed right on them.
 
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OK, not sure exactly how to "take the amp out" but I think this is the part (# C47) you're talking about, right? Not sure what the A/B/C stuff is all about...
chassis_bottom_view.png capacitors.png
 
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The ABC stuff is a multi section capacitor.....so more than one cap in that component.....it needs to be replaced with either a similar cap....or individual caps...that match those numbers ( farads... and voltages )

Taking the amp out....is just a matter of unplugging any wires to the amp....and getting a screw driver or socket driver and unbolting it from where it is....and getting it out to work on.
 
OK, that sounds pretty basic. Anything I should worry about re. getting shocked? The system is completely unplugged but I'm wondering if there's any sort of charge remaining that I need to watch out for... Also looking for advice re. buying a replacement capacitor -- any recommendations? And by the way, I really appreciate all the help/advice so far!
 
You shouldn't have any shock hazard to worry about as long as it's unplugged. Those capacitors are lower voltage than the one's used in standard equipment which employ power transformers. Since this would be the source of the hum, it's bad or most likely open and usually won't hold a charge.
 
OK, folks, I'm at a point where I don't know what to do next. Dropping the amp down and turning it over was easy enough (all the wires are still attached), but I don't see an obvious way to remove the capacitor and my soldering skills are nonexistent. What's my next step here?
Zenith capacitor1.JPG Zenith capacitor2.JPG
 
Looking at the capacitor a bit more closely, it looks like there are 4 wires coming out of one end: blue, green, black, and red. Can I simply cut these wires at the end of the capacitor, then twist-tie the old wires to the new capacitor's wires (assuming they are similarly color-coded)? And what about removing the capacitor from that metal bracket in the middle? It looks like it's held in place by something like a rivet -- not seeing any way to loosen or open that bracket.
Zenith capacitor3.JPG
 
Write down which color is which before snipping any wires. Black is almost always common or ground. Look at the capacitor to see which colors are for which value.

From what I see, red = 300 MFD @ 200 VDC (Volts DC), green = 300 MFD @ 150 VDC, and blue is 60 MFD @ 150 VDC.

This filter capacitor has 3 individual capacitors built inside one unit. You can either buy one capacitor containing all 3 capacitors or you can buy 3 individual capacitors. Doesn't make a bit of difference except for room constraints inside or on top of the amplifier.

Since this needs to be replaced, don't worry about how to get it out. Just cut it out if you have to but keep notes on which color wires are for which value.

Example: The BLUE wire will connect to the 60 MFD @ 150 volts DC replacement capacitor(s) and so on.
 
Can I keep the original in place and just wire in a replacement (or several) that more or less hangs down below the amp? Won't be pretty, but the entire thing is out of sight anyway...
 
Any recommendations re. best places to buy these three capacitors? I'm struggling to find these combinations of capacitance and voltage... (And looks like buying all 3 in a tube/series is likely not worth the effort, although I did find an article about how to repack an old tube with new capacitors...)
 
Guys (apologies if any gals are on this thread), but I seem to be striking out... I've reached out to Just Radios, Antique Electronic Supply, and Meistertech Solutions and none of them have the capacitors needed. Realistically, can this thing be salvaged? Are there options that diverge from the schematics that I can try? Also, there is a smaller tube of capacitors next to the big tube (see C48A/B in the earlier screenshots of the schematic parts list) -- do those need to be "recapped" as well as C47A/B/C?
 
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