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Adding aux input on a tube console

mafoose

Member
2008-02-07 12:40 am
I recently acquired a Motorola ST-82A wall mountable phono am/fm stereo tube console.

It sounds great, the phono part needs a bit of work (sometimes slows down as it goes round, probably just needs to be cleaned and lubed since its gear driven), it's missing a knob, and the pots need to be cleaned.

I've heard of people using the phono part of other systems and modifying it for an auxiliary input. I'd like to do this as it's our living room stereo system and I'd love to be able to plug in a laptop or mp3 player to it. One of the previous owners added non proprietary external speakers connectors as well as speaker selection switches, so I don't really care about keeping it original.

On a side not, anyone have any ideas on where to find a service manual and schematic for this unit? Info seems pretty rare... It seems that you could download Bietman's Radio diagrams at one point but all the links seem to be down =(

Thanks in advance!
 
Thats really weird that it didn't show up in my Rider index software search engine. But then again, I didn't write the software.

This may be my fault somehow.

I am assuming you mean Beitman index, not Rider. Riders only goes up to about 1949.

You may have used the excel file that I made and posted on my website some years ago. I noticed a weird thing when looked for the ST82 yesterday, which may be what you found. When I searched using the AutoFilter mode of excel, it wont show anything for Motorola past model number HS-1061 when you use the drop down list. But the other models ARE there, you can see them, just not in the drop down list. I dont know why the spreadsheet behaves this way. I have backup versions of this spreadsheet that work fine. I will replace the one on my website some time later today.


On the other hand, if this is not the index you are talking about, then please ignore my babbling.
 
Robert McLean said:


This may be my fault somehow.

I am assuming you mean Beitman index, not Rider. Riders only goes up to about 1949.

You may have used the excel file that I made and posted on my website some years ago. I noticed a weird thing when looked for the ST82 yesterday, which may be what you found. When I searched using the AutoFilter mode of excel, it wont show anything for Motorola past model number HS-1061 when you use the drop down list. But the other models ARE there, you can see them, just not in the drop down list. I dont know why the spreadsheet behaves this way. I have backup versions of this spreadsheet that work fine. I will replace the one on my website some time later today.


On the other hand, if this is not the index you are talking about, then please ignore my babbling.

Yes, you are correct Robert, I meant Beitman's.
I don't have an Excel index, mine is an actual software program that allows you to search by manufacturer and model number. I have one for both Beitman and Riders. The Beitmans is called "Beitmans schematic search 1.0"
Glenn
 
mafoose :
No, your reader is not the problem, I am the problem, I did not extract the file properly. Apoligies to all who downloaded the file with the blank page.

Here is the correct file, I have double checked it.

As for suggestions for adding an input, I would leave the phono input as is, and add a new "aux" input for whatever I wanted. The exact method will depend on the type of rotary selector switch they have used, if it is a generic type with some unused positions then you could use them to connect your aux input. I doubt you will be this lucky. But even so, you could add a rottary swithc of your own, or even a DPDT toggle switch and put it between the existing mono-stereo switch S2 and the volume control pots. In other words centers of new switch to top of pots, one of the pair of poles of the toggle switch to your new inputs, and the other to the wires coming from S2.

The added switch would then be used to select from "Old radio" mode, ie use existing rotary switch to select from AM, FM or Phono, or "New Aux Input" mode, to play whatever to connect to it.

Whether there is physical room to do the mods is another question.
 

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