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 Post subject: Re: convert 78rpm turntable to play 33's??
PostPosted: Mar Thu 08, 2018 12:48 am 
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Joined: Nov Sat 11, 2017 12:07 pm
Posts: 5
Location: South Manchester UK.
Memories!

My first record player at the age of fifteen, was actually a pre WW2 table-top phonograph. It only played 78s.
There was a speed adjustment that allowed you to alter the speed slightly with a sliding lever.

So I had a look inside and found that all this lever did was to apply increased pressure on three felt pads that rubbed on a flywheel, there was also a gimble that governed the motor speed. All I had to do was to remove the screws at either end of the plate that restricted the movement of the lever. I was then able to slow it down, to any speed I chose, but had to guess what was 33rpm and 45rpm. Whatever speed I selected, it ran at a constant number of revolutions, no "wow" at all.

I also changed the pick-up arm and cartridge. I had it for a year and didn't set the house on fire once.


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 Post subject: Re: convert 78rpm turntable to play 33's??
PostPosted: Aug Tue 14, 2018 10:13 pm 
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Joined: Nov Wed 27, 2013 5:59 am
Posts: 548
Location: Metzger Oregon
One more update, should anyone be following along. I finally had a little more free time to devote to this project, and I recapped the amp and connected the motor wiring properly to the Airline 74WG-2004A that I mentioned before. I ran the motor for about 2 hours listening to 2 albums all the way through, plus a few tracks off of a couple other albums. I had no problems, everything worked as good as a record player designed for 33 RPM.

In summary, and to David's point, I think the key to success here is to have a tone arm that tracks light enough and has low friction allowing it to easily track the record. Ideally, this would not be done to a changer with a trip mechanism as this would likely add too much friction. The speed of the Alliance motor was easily reduced and the Shure light weight cast aluminum tone arm works well for this application. As mentioned in a previous post, this project started out with me wanting to make an attachment for use with old radios using a salvaged Alliance turntable, modified for 33 RPM. I think this same setup is going to work perfectly for that.

Thanks everyone who posted information and the links to the Popular Electronics articles!


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 Post subject: Re: convert 78rpm turntable to play 33's??
PostPosted: Aug Thu 23, 2018 12:49 pm 
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Joined: Apr Tue 07, 2015 8:31 pm
Posts: 224
Location: Blue Lake, ME
Interesting topic. I’m glad to see the technique worked out. I’ve got a few 78 only
players gathering dust that need a new life. I’ll do the math to get the shaft in the ballpark,
but it looks straight forward. The weight of the original tonearm hasn’t been much of a
problem for me since most I’ve encountered float once the heavy crystal cart is removed.


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 Post subject: Re: convert 78rpm turntable to play 33's??
PostPosted: Aug Fri 24, 2018 4:19 am 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 2811
Location: Tucson, Arizona U.S.A.
The weight of the arm isn't the only problem. Friction in it's pivots can be the main difficulty.

_________________
Jim Mueller


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