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 Post subject: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Tue 03, 2018 4:33 pm 
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Hello everyone,
I have inherited a Motorola Stereophonic from my grandfather. I am interested in getting it restored, however I'm having a difficult time finding the model number. It isn't located anywhere on the back. Any tips you can give me would be greatly appreciated.

Thanks!


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Tue 03, 2018 6:43 pm 
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Location: Annapolis, MD
Please post some pictures.

It might be necessary to remove the back cover to see a model number

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Tue 03, 2018 9:50 pm 
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If its what I think it is these sound fantastic


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Tue 03, 2018 10:19 pm 
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I am having a hard time uploading pics, so here is a link to a few http://imgur.com/gallery/sbkMJVn

Thanks!


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Tue 03, 2018 11:11 pm 
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I'm familiar with these. Its a 3-channel Motorola. It features a center bass and a right and left channel. The amp probably uses a set of 6 EL84/6BQ5 output tubes and 3 12AX7's too.

If you are not familiar with how to restore these then you should either find a local person who knows or if feeling adventurous or have patience post it here and we can help you. Just be aware that these operate on high DC voltage and if you don't know what you're doing you can get hurt. Seriously.

What it will need is a recap job. The amp has a single electrolytic capacitor can with 4 sections. You will need to replace that with 4 individual capacitors.

So first order of business: Uncrew the back, take some pictures and let us take a look.


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 12:32 am 
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You can post photos as attachments straight out of the chute. No need to wait 24Hrs.
Posting photos to a forum thread...
The skinny: viewtopic.php?p=2717120#p2717120

Greg.


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 2:12 pm 
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mine is not the 3 channel one, but it is a similar beast.

it sounds absolutely wonderful after restoration.

viewtopic.php?f=1&t=341427

steve

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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 2:40 pm 
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Here are a couple pictures of the inside.
http://imgur.com/gallery/YyopCSN


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 2:40 pm 
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Here are a couple pictures of the inside.
http://imgur.com/gallery/YyopCSN


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 5:04 pm 
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Here it is:
https://www.radiomuseum.org/r/motorola_ ... 68_hs.html

schematic here (page 101-----( 103 in the pdf ) )
https://www.americanradiohistory.com/Ar ... n-1960.pdf

Don't operate it until it has been serviced

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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 5:18 pm 
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Thank you so much!


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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 5:35 pm 
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that is almost the same amplifier that is in my stereo SK14M version.

does the extra transformer for the third channel split off between the two channels ?

i wonder if it is the same output power as my SK14M since the output transformers are smaller ?

steve

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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Wed 04, 2018 8:21 pm 
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There's a low-level crossover, splitting the two stereo channels into two treble channels and a mono bass channel. Push-pull bass amp for about 12W, single-ended treble amps for about 4 watts each. Some versions had a reverb tank which fed into the center channel.

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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Thu 05, 2018 5:59 am 
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got it, thanks.

steve

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 Post subject: Re: Help finding the model number of a Motorola Stereophonic
PostPosted: Jul Fri 06, 2018 7:10 am 
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Joined: Mar Mon 05, 2012 6:35 am
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Location: Chicagoland, 60194
Tom Bavis wrote:
There's a low-level crossover, splitting the two stereo channels into two treble channels and a mono bass channel. Push-pull bass amp for about 12W, single-ended treble amps for about 4 watts each. Some versions had a reverb tank which fed into the center channel.


I've got one of these and just drug it down my basement stairs about a week ago from my storage place. The vibrasonic reverb uses a Hammond Organ supplied spring thing just like the Fisher K10 Spacexpander. The output from the reverb has its' own small amp and drives a small center speaker so there are 4 independent audio output paths. I haven't touched it since dragging down the stairs so I have no idea what it sounds like, but it has a lot going on.

Matt


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