Author Topic: Magnavox 1-ST-621 Danish Classic  (Read 1142 times)

Offline 19and41

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Magnavox 1-ST-621 Danish Classic
« on: November 29, 2017, 03:31:17 PM »
I landed my next Magnavox console, a newer 1963 unit.  One of the last tube architecture models and a stereo console.  It has 6 speakers, including 2 12 inchers.  I am starting to sift the components out of the dirt inside.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline RotarDad

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #1 on: November 29, 2017, 11:27:46 PM »
Sounds very cool!  We’d love to see a pic or two.....
Paul

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #2 on: November 30, 2017, 12:06:28 AM »
It'll be a few days, I have it in the garage and can't get a proper picture just yet.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #3 on: December 18, 2017, 04:32:51 PM »
I have come to the last chassis in the console to perform a replacement of the capacitors in.  Two of the capacitors have ruptured and of all places, in the stereo demodulator.  This is what can happen when one must play a 54 year old tube architecture console.  It must've went from a bothersome hum to a loud 60Hz buzz.  They were in exactly the values I don't have, and owing to the nature of the circuit, I want a replacement of the same value.  This will be the 3rd set of capacitors I've had to get for it. 
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline LarryInMichigan

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #4 on: December 18, 2017, 05:48:28 PM »
Are these electrolytic capacitors?  Are they rated for a high enough voltage for the application?  Were they connected with the correct polarity?

Larry

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #5 on: December 18, 2017, 06:01:52 PM »
These were OEM capacitors.  One was an electrolytic, the other was what appeared to be a paper wound.  Each were correct according to the parts list.  It was just what sometimes happens when the unit is operated with aged capacitors.  Before I could advise them not to, they turned it on to show me the horrible noise it made.  That was probably those failed components doing their thing.  Soon as I get the last two replaced, it will have current, safer capacitors and the quiet parts will be quiet and the music will be loud.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #6 on: January 09, 2018, 06:03:47 PM »
I know it's been a while, The weather hasn't been cooperating, either.  I've been able to do some more cleaning and finishing on the cabinet and I have each component recapped.  I will now have to install and reconnect the components and when I disassembled the unit I took detailed close ops of everything as it was.  Now, in going to review the pics, I find the SD card has failed.  So I am awaiting the assistance of a very knowledgeable person to help me with integrating the added FM demultiplexer assembly into the system.  The unit also had some bad staining on the top sliding covers, and I have been working on those  to get them at least looking like they haven't been saturated in adult beverages.  At least none infiltrated the unit in any critical areas.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #7 on: January 23, 2018, 02:19:10 PM »
I have put the unit back together as best I could and I can't get audio.  Not a scratch, click nor pop.  I am getting meter deflection on the receiver, so I know it is receiving.  The amp is getting at least the filament voltage, as is each of the other assemblies.  I have completed the check back of the work I have done to insure it is correct to schematic.  I also found the heavily obscured the teeny tiny tag that confirms it's model number.  There is a bit of complexity as there is a harness of interconnects for the power circuits as opposed to the signal circuits, the former being conveyed by molex connectors and the latter by RCA plug cables.  I can't find a schematic of the receiver to match my unit.  It's always something, as Rosanne Rosanadanna used to say.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline HarrySmith

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #8 on: January 23, 2018, 02:22:42 PM »
I am sure a schematic is out there somewhere. Maybe try to find a forum on these things and ask there.
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #9 on: January 23, 2018, 02:56:49 PM »
I'll get it straightened out one way or the other.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #10 on: January 30, 2018, 02:52:59 PM »
I went back through the unit, toned out the speakers, put an Mp3 player on the amplifier inputs to test through to the speakers and eliminated all but the receiver assembly.  I finally found it was the dual audio amplifier output tube.  The filament opened up.  I ordered a new one from a seller in Valparaiso IN and I have found the post office is taking it on a traveling holiday along the roads of north Georgia.  Just what a tube with a double long filament needs.  I am also getting space for the console in the living room, on Saturday.  Maybe I will have a functioning tube in hand by then.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #11 on: February 22, 2018, 03:58:24 PM »
Well, the filament hadn't opened up.  I found that my tube tester would not work with 6EU7 tubes.  So I had to wait on another tube tester that is working quite well.  The problem still remains with the tuner/ receiver.  It will not even pass audio to it's output to the amplifier. The amp also sets up the B+ voltages, that are trunked through the system between assemblies.  I want to make sure those potentials are correct before tracing through the tuner.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline HarrySmith

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #12 on: February 22, 2018, 06:56:17 PM »
Did a quick search on it and found a forum with lots of info. Audiokarma.org
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline 19and41

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #13 on: February 22, 2018, 08:14:35 PM »
Thanks, I'm a member.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Offline HarrySmith

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Re: Magnavox 1-ST-621 Danish Classic
« Reply #14 on: February 22, 2018, 08:17:25 PM »
OK, that makes sense!
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"