Author Topic: Magnavox 1ST223F Restoration Help!  (Read 531 times)

Atreides

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Magnavox 1ST223F Restoration Help!
« on: February 23, 2017, 05:49:05 PM »
So I recently picked up this little guy and have been working on going through it. It has an AMP 196 in it which I've replaced the tubes, filter capacitors and the coupling capacitors. I'm still having some issues and I think I'm as far as I can go on my own being as much of an amateur as I am. I have all the basic tools necessary including a cheap digital multimeter and soldering iron but unfortunately no oscilloscope. Any help would be greatly appreciated!

Before I replaced the capacitors and tubes very faint sound could be heard when it was turned all the way up. Almost like nice light background music with your ear right up against the speaker. Since the replacement the sound is much louder but still no where near what I would expect (or want!). Now it's nice background music while standing in front of the console but that's with the volume cranked all the way up. Another symptom is that when I turn the balance all the way to channel 2 the volume significantly decreases. Thoughts?

I will also be posting in the Wanted sections for some new 12's so if anyone has a line on a couple that would be great! I'm only sure that one needs to be replaced so far but I figure if I'm getting one I might as well grab two. The reason for replacement will be obvious from the picture.

Thanks again for any help and patience as this is my first project with older electronics.

TC Chris

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Re: Magnavox 1ST223F Restoration Help!
« Reply #1 on: February 23, 2017, 06:44:01 PM »
Your speaker's cone has come unglued along a glue line.  You may be able to salvage it by re-gluing.  Others may have better ideas but I have used "white glue" (Elmer's).  The repair will only fail if the voice coil has moved so it rubs on the central pole piece.

For the amp, check all the voltages at the tube socket pins.  They will be shown on a schematic.  You did not show a photo of the tuner/preamp.  You may find that the problem lies there.  If the decrease is on phono only, not on FM/AM, then it may be a faulty phono cartridge.  If it's the same on all inputs, it's elsewhere. 

Chris Campbell

Atreides

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Re: Magnavox 1ST223F Restoration Help!
« Reply #2 on: February 23, 2017, 07:06:42 PM »
I haven't been able to find the schematics for the 196. The 197 looks pretty darn close. What are the chances the values would be the same? I've tested it with an iPod plugged into the phono input and directly plugged into the amp inputs with no difference between the to. I suppose that's a pretty good hint. Perhaps I will change the capacitors and tubes in the pre-amp as well.

I'll give some glue a try on the speaker. It would definitely be nice to use the ones I have.

Any ideas on what would cause the output difference between the two channels?

electra225

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Re: Magnavox 1ST223F Restoration Help!
« Reply #3 on: February 23, 2017, 08:54:50 PM »
Function switch!!  Clean the function switch.  Also check to see if there is an external speaker switch.  Sounds like it might be in the "external" only position.  I would use speaker cement and a coffee filter to fix that speaker.  After it is dry, you could shoot it with a black spray bomb so the repair would be not so noticeable.  The original speakers or something really close should be available by the truck load on ebay.  Best of luck to you. 
If it ain't broke, call me.  I can break it....

TC Chris

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Re: Magnavox 1ST223F Restoration Help!
« Reply #4 on: February 23, 2017, 11:28:08 PM »
Function switch!!  Clean the function switch.  Also check to see if there is an external speaker switch.  Sounds like it might be in the "external" only position.  I would use speaker cement and a coffee filter to fix that speaker.  After it is dry, you could shoot it with a black spray bomb so the repair would be not so noticeable.  The original speakers or something really close should be available by the truck load on ebay.  Best of luck to you.

Actually, in the photo, the speaker isn't torn.  It's unglued where the edges of the cone overlap.  No filter paper needed.

Chris Campbell

Atreides

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Re: Magnavox 1ST223F Restoration Help!
« Reply #5 on: February 26, 2017, 08:39:37 PM »
Found it! The pin that goes to the output plates on the preamp were only getting 7V when it should be getting 100V. I wired it straight to the 265V with a couple resistors so now it's getting the proper 100V. Now it's too loud for my age and I'm only in my 30's!

I do have a new issue though. There's a pretty good hum at any volume. I assume it's one of the resistors since that's what I've seen as an explanation for hums but I was hoping someone could narrow it down for me.  Unfortunately I didn't find anything in other topics with a quick search.

TC Chris

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Re: Magnavox 1ST223F Restoration Help!
« Reply #6 on: February 26, 2017, 08:56:22 PM »
Maybe you picked up your B+ for the preamp plates from a bad spot?  I'd go with the original design arrangement.

Chris Campbell

electra225

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Re: Magnavox 1ST223F Restoration Help!
« Reply #7 on: February 26, 2017, 09:53:45 PM »
I'll second Chris' warning.  Kluges and hacks always come back to bite you.  Find out where you lost voltage, then fix it per the schematic.  No schematic?  Don't plug it in again until you get the correct schematic and can put the circuit back like it should be.  Good luck.
If it ain't broke, call me.  I can break it....

Atreides

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Re: Magnavox 1ST223F Restoration Help!
« Reply #8 on: February 26, 2017, 10:46:26 PM »
Judging by the schematics for the 197, which seems basically the same as the 196, I must have connected a wire to the wrong post when changing the filter capacitor can. The one to the posts for the preamp plates, posts 1 and 6, is supposed to go through a 470k resistor and then to 265V. I had accidentally ran it to a post that was only giving 7V. Rookie mistake for sure.

Any thoughts on the hum?

electra225

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Re: Magnavox 1ST223F Restoration Help!
« Reply #9 on: March 05, 2017, 10:52:01 AM »
You may quite possibly have damaged the filter cap when you wired it incorrectly.  A hum not affected by the volume control is typically found in the power supply somewhere.  My suggestion would be to sub a different capacitor of the correct value and voltage for the one that was mis-wired and see if that improves matters.  Good luck.
If it ain't broke, call me.  I can break it....

Atreides

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Re: Magnavox 1ST223F Restoration Help!
« Reply #10 on: March 05, 2017, 08:03:34 PM »
I figured it out actually. I also glued the speaker and the console is now sounding great in our living room!

Thanks for the help and time!

TC Chris

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Re: Magnavox 1ST223F Restoration Help!
« Reply #11 on: March 05, 2017, 08:57:27 PM »
I'm happy to hear that you've got music!  I went back to look at your photo again.  One thing that struck me is that Magnavox used the same decorative hardware on the front that was used on my Dad's 1951 console.  It seems to pop up on lots of others, too, including my 1956 model.  On the '51, there's a little key handle shaped device that's the door pull.  On the '56, it's just  a decorative escutcheon.  But Magnaovox either made a very advantageous purchase on them long ago, or liked them enough to keep using them.  The device that's brown is the '51; the one with the Mustang behind is the '56.

Your photo also shows skis and snowboards behind.  You must be in the same latitudes as Michigan.  Hope you've got more snow than we have this year.

Chris Campbell

Atreides

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Re: Magnavox 1ST223F Restoration Help!
« Reply #12 on: March 06, 2017, 10:39:27 PM »
Wow they must have bought quite the load of those to use them one their consoles for a decade. This summer I'm hoping to refinish the wood on this sucker and will definitely include those in the refinished product.

Yep! Those sure are skis in the background. We live about 45 minutes from Tahoe. Our local mountain has gotten 679" of snow this year! Most in North America and a record. Needless to say, I have used up all my sick time.

TC Chris

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Re: Magnavox 1ST223F Restoration Help!
« Reply #13 on: March 06, 2017, 11:27:54 PM »
Wow they must have bought quite the load of those to use them one their consoles for a decade. This summer I'm hoping to refinish the wood on this sucker and will definitely include those in the refinished product.

Yep! Those sure are skis in the background. We live about 45 minutes from Tahoe. Our local mountain has gotten 679" of snow this year! Most in North America and a record. Needless to say, I have used up all my sick time.

My niece lives in Lake Tahoe. I've seen photos of this year's snow there--pretty impressive!  By contrast, our snow cover completely disappeared in Feb., even though I'm in lower Michigan's snow country.  My city maintains its own ski hills for kids about a mile from my house. We got a bit more last week but today's mid-50s temps did it all in again.  This is seriously inappropriate weather.  Perhaps next year you'll share the snow and not hog it all out there.

Chris Campbell

AlexanderMartin

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Re: Magnavox 1ST223F Restoration Help!
« Reply #14 on: March 06, 2017, 11:29:30 PM »
I've seen the glue fall apart on those all the time, it usually hardens and when the speaker moves, it cracks and falls apart. If I were you I'd add glue on the spider, as they like to come off from the frame and cause the woofers to buzz and sound blown, but that's just me.