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Is the tube heater in series with a phono motor or just a dropping resistor? If it is just a resistor, and you can't find a 25EH5, it would be easy to calculate the value for a resistor change, using ohms law (E=IR)
A 25EH5 draws 0.3A at 25V, so using ohms law to calculate a 100V drop from the normal 125V line implies a 333 ohm series resistor.
A 50EH5 draws only 0.15A, but at 50V, so a 75V drop is needed. A 500 ohm would be the value for the series resistor.
hope this helps,
jr
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