Turntable strobe 120/240V power supply

[Airprodigy]

This is a query about the strobe for the Thorens TD125 turntable. This can be used without modification in both 120 and 240V regions save for changes to wiring on the mains board/transformer. The strobe has a built-in 47k series resistor. The transformer (dual primary/secondary) is the same in both voltage regions.

Since the series resistor is not changed the strobe will need a 240V supply. How is this achieved in a 120V region? The schematic seems to show 120V connected across one of the primary windings and the strobe connected across both windings to get 240V, ie a step-up arrangement. Is this a recognised way of using the primary coils? I can't find any other instance of this kind of use on the web.

 

[MikePP]

It’s a neon right?…. Change (or at least move it so it’s connected to the 110) the resistor to suit

It doesn’t need 240 to strike , hence the resistance

 

[NareshBrd]

Neons run at 60-70 V, hence always a series resistor is used for mains operation..
Check up, you need a smaller value for 110 compared to 220V

 

[johnmath]

If you look at the circuit you will see that the neon circuit is connected across the 220V winding of the multi-tapped transformer input. When the fuse is placed for connection to 117V input the neon circuit still gets 220V.

 

[MikePP]

If you look at the circuit you will see that the neon circuit is connected across the 220V winding of the multi-tapped transformer input. When the fuse is placed for connection to 117V input the neon circuit still gets 220V.

Oh yeah couldn't see that with that small picture ! well spotted that man


The resistor will still be fed 240 (autotransformer style) from the 120 winding when you move the fuse.

 

[Airprodigy]

Thanks for your replies. I assume in this autotransformer mode the power supplied by the transformer to the output will be reduced, eg from 15VA to 7.5VA?

 

[MikePP]

Just higher current on the primary with the change from 240 to 120


The neon takes negligable current and is via the primary anyway.

 

[RJM1]

I rebuilt my TD-125 about 10 years ago, bought new in 1975. The strobe had nerer worked right ( It flickered).
I am on 120V. The power supply voltage were correct but I was only getting 120V out of the transformer before the 47K resistor to the neon lamp. Bad transformer from the factory. After I replaced it the strobe worked fine. I guess that they sent the turntables with a bad primary for 240V to the 120V market, or I was just unlucky.