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 My new old Magnavox Stereo Theater

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wildcat445
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PostSubject: My new old Magnavox Stereo Theater   July 7th 2018, 2:58 pm

I have been looking for a Stereo Theater for about three years.  There were not that many built, and, unfortunately, the console rapers and guitar amp crowd has parted many of them out for the amplifier, typically a 9300 series 15 WPC tube affair.  This thing has proven more elusive than a Concert Grand was.  Combine this with the fact that the TV is black and white, this makes their survival chances rather slim.

I have no idea why I thought I wanted one.  I certainly do not NEED one.  They are such a work of art and a statement of pinache and class than they have always intrigued me.  And it fills a gap in my Magnavox collection.  The one I got is a circa 1962 model 1MR418M, equipped with factory ultrasonic remote control.  Rather a bizarre system, really.  The remote only controls the TV, oddly enough.  The factory price of $795 put this Stereo Theater in the price range between my Imperial at $695 and the Concert Grand at $995.  The Stereo Theater came standard with MPX adapter, while the other Magnavox stereos had optional MPX at $35.  If you had either indoor plumbing or a three-hole privy, wall-to-wall carpeting and a Stereo Theater, you was rich folks!  If you had this stuff plus air conditioning, you was REALLY rich folks!

This Stereo Theater electronically will be between the Symphony and the Imperial.  It is basically a little Imperial with a 27" TV set in the middle of the cabinet.  This particular instrument is said to have a nasty hum in the audio, which will be my first area of investigation.  The top of the cabinet rails have had a hard life for some reason and the cabinet could use a thorough cleaning.  If I can figure out how to add a couple pictures, I'll do that.  I am going to give this thing a thorough restoration, every part.  If there is interest, I'll share my progress with you.

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This instrument is 32" high, 19" deep and 60" long, two inches longer than the Concert Grand.  While other manufacturers were making "aircraft carriers" sometimes up to 8' long, Magnavox kept the cabinets reasonable in size.  I'm told this weighs north of 200 pounds, but it is on casters, like most of Magnavox's big sets.  The inside of the cabinet is crammed with electronics and lots of dangling wires.

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ve1arn
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PostSubject: Re: My new old Magnavox Stereo Theater   July 8th 2018, 4:42 pm

That is a nice looking set! I can see why the attraction is there. It would be a great piece to watch the older black & white TV shows on. Heck, I would probably even be tempted to lay down on the floor in front of it to watch it too, just like when I was growing up. Very Happy Very Happy
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PostSubject: Re: My new old Magnavox Stereo Theater   July 14th 2018, 9:27 am

If I were to lay down on the floor to watch TV, they might have to call the EMT's to get me back up!  Rolling Eyes

This thing will need an "every wire, every part" as thorough a restoration as I can muster.  I am looking forward to the project.  The most complex electronic restoration I have attempted to date.  This thing will make my Concert Grand restoration look like a day in the park.  I have never messed with TV much..

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PostSubject: Re: My new old Magnavox Stereo Theater   July 18th 2018, 8:38 pm

That is a mighty attractive cabinet.  Your pics look more promising than the first ones you put up.

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PostSubject: Re: My new old Magnavox Stereo Theater   July 19th 2018, 3:16 pm

This is a slow process.  I'm going wire by wire and making sure everything is right before I even power it up.  I've got to order some caps before I can do anything else.

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ve1arn
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PostSubject: Re: My new old Magnavox Stereo Theater   July 19th 2018, 3:38 pm

Yeah! But think what you'll have when you're done.
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Cliff Jones
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PostSubject: Re: My new old Magnavox Stereo Theater   July 19th 2018, 3:38 pm

Now all you need is a Turntable.

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PostSubject: Re: My new old Magnavox Stereo Theater   July 19th 2018, 4:40 pm

I have a turntable.  Actually, it is right above the amplifier I've been working on.  It'll be a year before I tinker with it.  This is the first Magnavox stereo I own that does not have an EV 26 cartridge in it.  I think this one is an EV 150, but I won't swear to that.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 17th 2018, 7:19 pm

I bought my Stereo Theater knowing it had a problem.  A "bad" hum.  I did not plug it in before I tore into it.  I started in the amplifier.  I soon learned some things.  First, "happy hands at home" had been hard at work.  The normal sloppy Magnavox wiring was even sloppier than normal.  I have only found four original tubes out of the 36 in the instrument.  Radio Shack Realistic Lifetime tubes were in everything.  The power transformer had been replaced.  The wires had been twisted together and taped.  All the capacitors in the instrument were original, every last one.  I replaced all the electrolytic filter caps, the cathode bypass cap, the cathode bias resistor, all the 220K resistors in the amplifier, the two electrolytic plate bypass caps in the tuner, the cathode bypass caps in the tuner, three or four paper coupling caps.  I still have a hum in the Multiplex adapter, so I need to get it out and onto the bench.  I have not really gotten into the TV a lot past just looking things over.  The damper socket has been hot, so I'm going to replace it.  Most of the caps on the top of the PCB chassis are mylar, so i'll leave them alone until I see a need to replace one or all.  There are a number of paper caps on the back of the vertical chassis that will be replaced.  It sounds pretty good.  I believe if I can get the TV sorted, this thing will be a sweetheart.  Next summer the plan is to gut the cabinet and refinish it.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 17th 2018, 7:41 pm

It looks pretty good so far. Is that burned socket in the second pic a ceramic?

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Rod Clay
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PostSubject: Re: My new old Magnavox Stereo Theater   August 17th 2018, 11:31 pm

Interesting description of the set and your restoration efforts on it so far. I'm sure we all wish we could be there while your working on it. 

I was wondering too if that octal damper socket was a ceramic or maybe a plastic one. I've seen some of those in TV sets. Could there have been some arcing going on? I am wondering about the pin out of the damper tube. That would give an idea. Would it be a 6W4 or something like that? 

73, Rod  N4QNX
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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 4:33 am

The burned socket is not ceramic.  Looks like regular plastic or bakelite to me.  I don't see anything else at this point that has been hot.  Everything else looks good, just really dirty on the back side.  I am still waiting on service information for this thing.  The tube that is there is an RCA 6AU4.  The tube that should be there is a 6DA4.  Depending on who I ask, pin 2, the one that is most burnt, is the filament for that tube.  Or not used at all.  Who knows?  A schematic will guide me as to what pin 2 does and perhaps give me some indication on what caused the burning.  The tube looks like new, which I suspect it is relative to the burning of the socket.  My guess is this condition put the TV on the fritz.

My  buddy Ron is salivating over the prospect of refinishing this huge cabinet.  Most of it comes apart.  The front sliding panels are nailed together.  There are two kinds of grille cloth on this thing.  There is not a dent in the cabinet anywhere.  The stain is variable in most spots.  I have some questions yet to answer, but the basic plan is coming together.  Don't tell the snoots on ARF, but this thing will get one of my famous polyurethane over shellac finishes.  Magnavox did not use lacquer.  Poly, properly worked, is the only finish I have found that duplicates the milky, creamy oil finish that Magnavox applied at the factory.  The only downside I see to poly is that you have to let it cure at least a month before you can work it and put the cabinet back together.  That is like urethanes were on automotive finishes as well.  It lasts forever and is impervious to almost everything.  I have a cat that sleeps on the 616 I refinished with no damage whatsoever.

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Rod Clay
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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 7:51 am

I did some checking on the damper tube situation. The 6DA4 data sheet says pins 1 and 2 are internal connections. Pin 1 may be omitted. Pins 7 and 8 are the filament connections. Pin 3 is the cathode and 5 is the plate. 

The 6AU4 could be a sub for a 6AD4. It has similar connections although the 6.3V filament takes .6 Amps more current-not good on the power transformer. The data for the 6AU4 shows pins 1 and 2 have no connection and again pin 1 may be omitted. 

The data says no connections should be made to socket terminals 1, 2, 4, and 6 for both tubes. Hope this helps.

Rod
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wildcat445
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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 11:10 am

It does.  Thank you.  Any theory on why pin 2 in the damper socket is the most burned?

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Rod Clay
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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 12:10 pm

Well, I'm not an expert on older TVs but I do know that the damper cathode (3) is subject to high voltage pulses coming from the flyback transformer which would put a lot of stress on that socket. Then there is the internal connection of pin (2) of the 6AD4 to think of. Presumably, the set has had a 6AD4 in it for most of its life. Maybe when you can get behind the chassis and inspect the back of the socket you'll see some signs of arcing-that will tell you something.
Rod
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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 12:15 pm

It may have been a loose, high resistance pin socket.  You can get a overheated connection on a bulb's filament line, I would imagine it could be possible with a tube as well.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 18th 2018, 2:29 pm

I need to get the TV chassis out to really tell, but I'm beginning to think like you guys.  Probably started out as a loose connection that went unnoticed until it was too late.  If you'd see this in person, I don't believe there would be any doubt that it stopped the TV from working by killing the high voltage.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 20th 2018, 5:35 pm

I am currently knee-deep in the Multiplex adapter.  This is a source, perhaps THE source of the hum I have been chasing.  This stereo may be even sweeter than my Symphony, and that is saying something.  It currently has the nicest-sounding record player that I own, outside of the newer component equipment.  I still have time to ruin it, and may considering my changer repair skills.  This multiplex adapter is different from the two-tubers in that there is a gain control buried under the chassis along with a balance control, with a knob on one skirt of the chassis.  My procedure will be to replace the [email=30uf@350]30uf@350[/email] plate bypass electrolytic cap and the [email=4uf@50]4uf@50[/email] volt coupling cap.  Then test tubes, make sure all the grounds are intact, then see what I have at that point.  I have tried using a redundant ground between MPX and chassis and between MPX and amp.  That did not improve matters.  My theory at this point is that the hum is electronically produced, hopefully by the leaky e-caps mentioned above.  I have a low-level hum that should not be there.  Changing the audio cables from MPX to tuner has eliminated the motorboating.  I'm thinking the problem is a simple one, and, by checking everything and eliminating possibilities, I should be okay.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 20th 2018, 5:44 pm

There are a few tiny e caps in those.  I had to hit Ebay for replacements as I found each of them.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 20th 2018, 9:05 pm

I have a supply of those little 4uf caps on hand for other Magnavox Multiplex adapters I have gone thru.  This one is a little different from the older, two tube models.  There are no paper coupling caps.  Everything that is not an e-cap is a ceramic.  I want to be sure to check the 47K ohm resistors in the cathode circuits.  This one had its output connected to the tape output RCA jacks on the tuner.  That caused a hum in every position of the function switch.  I did not find anything in the tuner than it hurt.  I'll check for potential damage in the Multiplex adapter.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 21st 2018, 2:27 pm

I replaced the electrolytics caps I mentioned above, cleaned a couple of control pots. and replaced all the tubes.  The hum is finally gone.  I have good performance and am satisfied with how it is coming along so far.  The TV is next.  I'm going to save the changer repair until after the cabinet is done.

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Rod Clay
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PostSubject: Re: My new old Magnavox Stereo Theater   August 22nd 2018, 7:45 am

For phono restoration info and tips check out RADIOTVPHONONUT on youtube. He has done a lot of repair/restoration videos on record players. I'd say phonographs and record players are his favorite repair subject. Disassembly, cleaning, lubrication, reassembly and cartridge replacement seem to be the routine. He can do radios and vintage TVs too. Fun to watch.

Shango066, also at youtube, is really good at getting old vintage B&W and color TVs going again. He does this mostly for fun and travels widely to pick up interesting sets for demonstration in his videos. He uses a brute force service technique to resurrect badly neglected sets he finds. 

He also does a good job explaining the effects of aging on tv components such as individual pots and grouped controls. 

Beyond getting these old junkers going he is capable of doing further, more complete restoration work on the more interesting sets. He appears to be very knowledgeable on old TVs in general. He knows how to do the setup and adjustment routines necessary after repairs have been made especially on color sets. Like radiotvphononut, shango066 has little interest in fixing modern radio-tv equipment.

Good luck.

73, Rod  N4QNX
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PostSubject: Re: My new old Magnavox Stereo Theater   August 22nd 2018, 8:47 am

I enjoy shango66 about as much as anyone.  My problem with his work is that he is such a sloppy worker.  He does not clean anything before he works on it.  He is full of knowledge and he always get whatever he is working on going again.  Bandersen is a neat worker and I enjoy his videos.  His explanations are harder for me to understand.  He sounds like he is talking to himself.  I saw a post on Video Karma where a member, working on a Philco Predicta, replaced every resistor and capacitor in the set, whether it needed it or not.  I realize that a Philco Predicta was not the best TV chassis ever built, but I'm not sure that I could do that much work on a printed circuit chassis and not do more harm than good.  That got me to thinking about what I want to do with my Stereo Theater's TV chassis.  If I could find a NOS, NIB picture tube for it, then I might consider changing every resistor and every capacitor.  That SHOULD give me the equivalent of a brand new 1962 model TV set.  I might pull the chassis on my ST and take it with me this winter.  I could take all winter to change every capacitor and every resistor.  That would be a lot of heat on the printed circuts.....

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PostSubject: Re: My new old Magnavox Stereo Theater   August 22nd 2018, 10:11 am

Get a good solder extractor for the printed circuits.  I can help you set one up that will work great for you.

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Cliff Jones
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PostSubject: Re: My new old Magnavox Stereo Theater   August 22nd 2018, 11:55 am

If you clean the circuit board first by making a Bath of Rubbing Alcohol (91% is much better) Walmart is my goto store for that. It will not remove markings and colors. Get some Larger paint brushes, toothbrushes, and those cheap Acid brushes.

Let it soak submersed for at least 5 minutes, then start brushing to scrub off dirt, oils, flux.
Don't scrub hard, as you don't want to physically damage traces or components.

This was standard practice even in the 2M program for circuit cards.  click here



Then rinse of in a second bath, and either let air dry or blow off with low pressure air.
Note the alcohol will absorb any moisture which helps.

Now on soldering you need to use a very small solder pencil , Antex is one brand we used at Textronix in Beaverton.  Click here to see one model


Stay on the trace no more than 2-3 seconds with no pressure with the Iron.

Apply flux liberally before you solder, as it will make the solder flow easier. If you are worried about
parts that need soldering use heat clamps on the leads (tiny alligator clips come to mind).

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PostSubject: Re: My new old Magnavox Stereo Theater   August 23rd 2018, 9:37 am

Thank you both for your suggestions.  I saw a post on ARF where a member took his TV chassis to the car wash!  I'm not sure I'm that brave.  I like the alcohol idea.  That seems like it would do less damage to transformers and that.  Mine is not horrible, but not pretty either.  I'm mulling over the idea of replacing all the resistors with 1%, 1-watt metal film and replacing the caps with 1000 volt orange drops.  I have identified one and maybe two tubes with bad soldering on the tube socket.  I've read where it is vital to check the connections at chassis grounds.  It looks to me like the individual PCB boards can be removed from the chassis, like they do on Philco Predictas.

Although I believe my "jug" to be good, I believe the hunt for a NOS 27ZP4 is on.  I like that idea of having a brand new 1962 model TV.  I have enough tubes on hand that I could also supply the chassis with all brand-new RCA tubes.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 23rd 2018, 9:41 am

Your assumption is correct on not submersing Power transformers or choke transformers unless they are encapsulated or sealed from moisture
If there are coils that show no sign of sealant , then include them in not submersing other than Turret tuner coils as the are exposed bare wire usually.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 23rd 2018, 9:47 am

What about the small coils that are dispersed generously around that TV chassis?  Will alcohol hurt them?  Could I not just slosh alcohol on the boards, much like when you are cleaning car parts, and not actually submerge it?  Then dry it with compressed air.....

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PostSubject: Re: My new old Magnavox Stereo Theater   August 23rd 2018, 9:50 am

I would avoid compressed air on coils and let then air dry. A safer method would to set the card containing those in direct sunlight all day, as some coils are very delicate in the wire winding's.

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PostSubject: Re: My new old Magnavox Stereo Theater   August 23rd 2018, 9:51 am

Remember the wire may be hair thin in size.

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