# I need a resistor.



## Electraglide (Jan 24, 2010)

I'm modifying an old record player tube amp from 1950 or so.. It has a 25L6GT tube in series with the 90V motor. The motor is disconnected and probably going into another record player. I need a resistor to drop the voltage 90V 300ma. Yes, when I do this I'll put in an isolation transformer. I'll post a pic soon.


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## epis (Feb 25, 2012)

Well, it's gonna be very unusual, 300 Ohms power dissipation 27 Watts. You'll need one 50 Watts ( or more) resistor for that job.


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## greco (Jul 15, 2007)

epis said:


> Well, it's gonna be very unusual, 300 Ohms power dissipation 27 Watts. You'll need one 50 Watts ( or more) resistor for that job.


Along with a decent heat sink...I assume.


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## epis (Feb 25, 2012)

greco said:


> Along with a decent heat sink...I assume.


Definitely, but is it worth a trouble ? I don't know. I did a few tries with these string chained heater tubes, used big resistors with small fans, lower voltage light bulbs in series, transformers, to much hassle for the final result. I don't bother with it anymore.


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## Electraglide (Jan 24, 2010)

epis said:


> Definitely, but is it worth a trouble ? I don't know. I did a few tries with these string chained heater tubes, used big resistors with small fans, lower voltage light bulbs in series, transformers, to much hassle for the final result. I don't bother with it anymore.


I could hook the motor back up. As far as being worth it, I think it is. If nothing more than just doing it and making it work.


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## Lincoln (Jun 2, 2008)

How about some kind of "step-down" transformer rather than a resistor?


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## jb welder (Sep 14, 2010)

If you don't really need the motor for the other unit, then I like your idea of just leaving it in.
But that current number is not correct for the actual running conditions. The 50L6 heater current is 150mA, and it is in series, so that is your current.
You would need a 600ohm 13.5W resistor,one with a 20W rating will give you a decent safety margin.
It's still going to create a lot more heat than the motor will.


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## greco (Jul 15, 2007)

jb welder said:


> You would need a 600ohm 13.5W resistor,one with a 20W rating will give you a decent safety margin.
> *It's still going to create a lot more heat than the motor will.*


Voila!


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## knight_yyz (Mar 14, 2015)

If you look hard enough you can find high wattage resistors with built in heat sinks.


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## Electraglide (Jan 24, 2010)

jb welder said:


> If you don't really need the motor for the other unit, then I like your idea of just leaving it in.
> But that current number is not correct for the actual running conditions. The 50L6 heater current is 150mA, and it is in series, so that is your current.
> You would need a 600ohm 13.5W resistor,one with a 20W rating will give you a decent safety margin.
> It's still going to create a lot more heat than the motor will.


Is that for a 50L6 or for the 25L6GT that's stock in the record player. From what I can find out I should be able to use a 50L6 in the unit with a 1.2k 690 ohm 25w resistor in parallel. If I can find the proper grommets that will work in the motor for the 1950 Electrohome I might rewire it back in. One problem with this model of record player is that when it's turned on the motor is running.


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## jb welder (Sep 14, 2010)

I'm terribly sorry, I had 50L6 on the brain for some reason.
Epis had it correct, 300 ohm 27W, make it 50W for reliability.
But modern wall voltage is more like 125, not 115, so make it 330ohm and the tube will get it's proper 25V.
For a 50L6, you would use a 500 ohm in series, not parallel. Wattage should be more than 12W, 20 watt would be good.
Like knight_yyz mentioned, you can get the aluminum type for mounting on heatsink, but however it's done, all that heat still sits inside the chassis, so it may need venting. Higher wattage resistors just spread the heat better, it still remains there.


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## Electraglide (Jan 24, 2010)

http://i1000.photobucket.com/albums/af129/Electraglide49/lilamp_zpsktcakqk1.jpg
This is it, more or less. Not much of a chassis and no case, yet. Heat shouldn't be a problem. The resistor probably won't be in the chassis. For reference that's the original 4" speaker and the other tube is a 50L6GT. Why didn't I keep it as a record player? I have others and this one needed a new cartridge....at around $80. I can buy working record players for less. The motor ties in from the pin with the power wire to the next pin to the right.


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## greco (Jul 15, 2007)




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## Electraglide (Jan 24, 2010)

greco said:


>


Thanks. Got to figure out how to do that one of these years.


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## nonreverb (Sep 19, 2006)

I might have something like that although they're huge....


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