Author Topic: Schematics for a Magnavox AMP 820100?  (Read 9891 times)

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Schematics for a Magnavox AMP 820100?
« on: April 24, 2015, 04:25:16 PM »
Hello,

This is my first post (apologies if it is in the wrong place).  We recently acquired a Magnavox Concert Grand 1ST800F from 1959, and had it mostly restored.....mostly.  The left tweeter doesn't seem to want to work on the correct setting.  Either both tweeters work, and we only get mono, OR only one tweeter works, and we get stereo.  Of course the ideal is to get stereo, and both tweeters to work!  Our restorer is an old Hungarian guy, and he thinks the problem is with the AMPS.  He thinks he can wire it correctly if we can get a schematic for the AMP 820100.  Does anyone have this schematic?  Or any other ideas for us to try?  Thanks in advance for the help.

Pat L

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Re: Schematics for a Magnavox AMP 820100?
« Reply #1 on: April 24, 2015, 05:14:09 PM »
We have two manuals for your Concert Grand in our downloads center under Magnavox consoles. They both include full schematics. I'm a bit nervous about having to wire the amps so they work properly. In truth that is not something that really ever needs to be redone. Chances are the problem is more common and easier to fix than that.

Talk to people on this forum before you commit to a course of action.
Pat

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Re: Schematics for a Magnavox AMP 820100?
« Reply #2 on: April 24, 2015, 05:23:33 PM »
I would suspect a bad/dirty selector switch. Have all the controls been thoroughly clean and inspected??
-- Aloha, Ken

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Larry H

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Re: Schematics for a Magnavox AMP 820100?
« Reply #3 on: April 24, 2015, 06:04:42 PM »
The speaker switch is probably dirty and not making good contact.  It could also be a wire that's broken, or a bent connector in the speaker wiring that connects to the amplifiers.  I seriously doubt this problem is in one of the amps. I agree with Pat on that.
--Larry

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Re: Schematics for a Magnavox AMP 820100?
« Reply #4 on: April 25, 2015, 07:41:48 PM »
Are my posts getting through? I have tried to upload some pictures (less than 1.5Mb  each and less than 15Mb total) and it just gives me a white screen.

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Re: Schematics for a Magnavox AMP 820100?
« Reply #5 on: April 25, 2015, 07:42:19 PM »
First

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Re: Schematics for a Magnavox AMP 820100?
« Reply #6 on: April 25, 2015, 07:42:40 PM »
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Re: Schematics for a Magnavox AMP 820100?
« Reply #7 on: April 25, 2015, 07:43:08 PM »
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Re: Schematics for a Magnavox AMP 820100?
« Reply #8 on: April 25, 2015, 07:43:32 PM »
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Re: Schematics for a Magnavox AMP 820100?
« Reply #9 on: April 25, 2015, 07:44:02 PM »
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Re: Schematics for a Magnavox AMP 820100?
« Reply #10 on: April 25, 2015, 07:44:40 PM »
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Re: Schematics for a Magnavox AMP 820100?
« Reply #11 on: April 25, 2015, 07:45:46 PM »
Back of console (just for kicks)

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Re: Schematics for a Magnavox AMP 820100?
« Reply #12 on: April 25, 2015, 07:46:50 PM »
Thanks for the tips, guys.

My repair guy also seemed to think it at least worth while to try and clean the speaker selector a bit. I originally paid him to restore it which he mostly did (cleaned, recapped, tested/replaced tubes, etc) but I get the feeling he is no longer anxious to work on it. His request for the amp/speaker schematics was so that he could have a better understanding of how it all worked as it does seem a bit more complicated than a typical tube stereo from that era.

In the mean time, I am trying to use some contact cleaner on the different speaker selector connectors to see if that helps at all. So far, no dice. Above are photos of the amps, speaker connectors and speaker selector wheel. Anything obviously wrong stick out to anyone?

Pat L

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Re: Schematics for a Magnavox AMP 820100?
« Reply #13 on: April 25, 2015, 07:52:29 PM »
Usually spraying the switch well with Deoxit or equivelent while moving the switch through its paces is enough. Another very common problem with these units is dirty tube pin and socket connections. Often by tapping the various tubes you can find the problem. It's usually the preamp tubes and the 12AX7's on the amps. To fix it pull the tubes and spray the sockets or pins with Deoxit and work them in and out a few times. Trust me, this is necessary.

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Re: Schematics for a Magnavox AMP 820100?
« Reply #14 on: April 25, 2015, 07:56:39 PM »
Pat,

Thanks for the tip. I did give the tubes a little tap while the unit was on and did not hear anything. I will try and give them a little contact clean as well and let you know (probably later this evening).

Thanks so much. I am frustrated because I am SOOO close.