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Purveyors of Electronic, Musical and Vintage goods from then, now and in between. 
Since 1982.

HOW TO MODIFY YOUR EXISTING TURNTABLE TO PLAY 78'S / 78 RPM RECORDS - ON THE CHEAP!

 

This is a technique we discovered when trying to modify a turntable / record player with an AC motor, and designed for North American 120V / 60Hz current to be a more correct speed with 50Hz power for a temporary 'art' installation (customer used a transformer to convert from 120Volts to 220-240 Volts, but one that converted the 'Hz' / power cycles was beyond the budget for the project). AND IT WORKED! We then deduced the same technique could be used to make a turn-table play at 78 RPM. THAT WORKED AS WELL!
Could also be used to correct issues with turntable running too slow, or slower.


 

 

 

         

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



This modification was carried out on a JVC JL-F30 turntable. It is a standard 'belt drive' table with a brass motor spindle. The following operations should work with most any 'belt drive' table that has a motor spindle that resembles the one shown in these photos.
 


Removing the platter should expose a mechanism similar to this. This is a typical '2-Step', 33 1/3 / 45 RPM turntable spindle / pulley. It's made of brass and is held on to the motor shaft with a set screw. Of course you could do the calculations and have a machine shop increase the circumference, but one of the words in the title of this page was 'CHEAP'...

 


Using simple vinyl electrical tape, we are going to wrap it around the motor spindle, which increases it's circumference, thus increasing the belt travel speed.


Using a razor blade and a steady hand, split the tape into a width appropriate for the 45 RPM (larger) section on the motor spindle.

 
 


Since the motor spins 'clockwise', the wrap should start on the left or 'leading edge' of the pulley.
 


Finished wrap for a simple 'speed correction'.


This was a short section of tape we used for 'speed correction', not 45 to 78 RPM conversion.
 


This was a longer section we cut to do the 45RPM to 78RPM conversion, just after starting the wrapping process.

 



We found it handy to put an index mark with a Sharpie marker to keep track of the number of wraps / turns. It was best to put the speed fork in the '45' position to make grasping the top of the pulley easier.


Then start wrapping...


Once wrapped it should look like this.


You could also use 'shrink wrap / tube' either the sheath the tape, or simply use successive layers of shrink tube in lieu of tape.

 


Here is the built-up pulley with the belt installed.


 


JVC belt drive turntable successfully playing a 78 RPM record.

Our speed testing was verified with strobe disc that showed +4%, +2%, 0, -2% and -4% results.


You would think by doing this that you would introduce a bit of 'flutter' to the sound of a turntable, and I'm sure on a minute level you do, but in testing with a 'test tone' record, there was essentially none detected. We have not tested the integrity of the tape 'long term', only for about 12 hours. Upon inspection after that time, the tape and it's leading edge showed no significant signs of wear. We found that 1 layer of tape = about 3% at the 45 RPM dimensions. 13 wraps on the 45 RPM portion of the pulley / belt spindle (about 6.5" of tape) resulted in 78 RPM at +2%, starting with a table that was already running at -4% prior to starting the mod (sorry, but we didn't spend the time to 'add tape' to get the table 100% 'dead-on', then add tape to get the 78 speed 'dead-on', but you get the drift.
You would still need to address the correct stylus / needle or entire cartridge replacement for playing 78 RPM records, as most cartridge / stylus / needle combinations designed for 33's are going to make 78's sound even thinner / tinney'er.



NO OTHER INFORMATION, NOR ASSISTANCE AVAILABLE


 
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ATTENTION: We recommend you DO NOT DISASSEMBLE  or ATTEMPT TO REPAIR OR REPLACE ANY PARTS ON ANY ELECTRONIC / ELECTRICAL DEVICE without proper, technical training and repairs / modifications should always be left to qualified technicians.
 

The information contained here is simply my personal findings and is not intended for anyone / or any entity to use to make any decisions to repair, disassemble, modify, or do anything. It is strictly for entertainment value. Please do not email any responses or call with any information related to it. It is also likely to change as new / additional information comes to light, or I change my mind or opinion. So There!

 


 

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