I would like to cut the line voltage down to 110 for these old radios instead of the 120 or so that we now have. Anybody have some ideas on how to do that?

Most of the old radios were designed for 117 to 120 volt use. Reducing the voltage to 110 will reduce performance notably, especially if the tubes are somewhat weak. Even
my 1930s NOMA Christmas lights are rated for 120 volt use.

If you wish to reduce the voltage, the simplest way is to use a resistor. For most modestly sized radios this resistor doesn't have to be too big, and probably a 10 watt rating will suffice. For instance, a 60 watt radio would require approximately a 20 ohm resistor to drop 10 volts. 5 watts would be dissipated.

For AC-DC radios, you can put a resistor in series with the filament string instead of the whole radio, since a slight increase in B voltage in these radios is unimportant. Actually, though, most of these radios have the filament strings calculated out for a mean operational voltage between 118 and 121 volts.

For 3-way portables it is better to put a resistor in series with the entire radio, since the amplifier tubes' filaments receive their voltage from the B supply. In many of these radios, though, you will find that the voltages all measure correctly when the radio is operated at 120 volts.

A reduction in filament voltage will certainly prolong the filaments. Don't get carried away. The cathodes must be heated to normal operating temperature.

Another trick for reducing the filament voltage in AC/DC radios is to add a pilot lamp, say, if an edge lit dial only has one lamp, or if a 3-way portable has no lamp at all. Don't destroy a radio that obviously can't take another lamp, though. The simplest way to add a pilot lamp is to string two 6.8-7.0 volt zener diodes back to back, and wire this in parallel with a #47 or 44 pilot lamp, depending on whether the radio uses .15 or .3 ampere tubes. This will drop about 6 to 7 volts, which is close enough.

Another trick that some use to protect the tubes is to use a thermister. This keeps the radio close to the normal operating voltage once warm, and brings up voltage slowly at turn-on. Thermisters can be used with both transformer and transformerless radios.

T.

:Most of the old radios were designed for 117 to 120 volt use. Reducing the voltage to 110 will reduce performance notably, especially if the tubes are somewhat weak. Even
:my 1930s NOMA Christmas lights are rated for 120 volt use.
:
:If you wish to reduce the voltage, the simplest way is to use a resistor. For most modestly sized radios this resistor doesn't have to be too big, and probably a 10 watt rating will suffice. For instance, a 60 watt radio would require approximately a 20 ohm resistor to drop 10 volts. 5 watts would be dissipated.
:
:For AC-DC radios, you can put a resistor in series with the filament string instead of the whole radio, since a slight increase in B voltage in these radios is unimportant. Actually, though, most of these radios have the filament strings calculated out for a mean operational voltage between 118 and 121 volts.
:
:For 3-way portables it is better to put a resistor in series with the entire radio, since the amplifier tubes' filaments receive their voltage from the B supply. In many of these radios, though, you will find that the voltages all measure correctly when the radio is operated at 120 volts.
:
:A reduction in filament voltage will certainly prolong the filaments. Don't get carried away. The cathodes must be heated to normal operating temperature.
:
:Another trick for reducing the filament voltage in AC/DC radios is to add a pilot lamp, say, if an edge lit dial only has one lamp, or if a 3-way portable has no lamp at all. Don't destroy a radio that obviously can't take another lamp, though. The simplest way to add a pilot lamp is to string two 6.8-7.0 volt zener diodes back to back, and wire this in parallel with a #47 or 44 pilot lamp, depending on whether the radio uses .15 or .3 ampere tubes. This will drop about 6 to 7 volts, which is close enough.
:
:Another trick that some use to protect the tubes is to use a thermister. This keeps the radio close to the normal operating voltage once warm, and brings up voltage slowly at turn-on. Thermisters can be used with both transformer and transformerless radios.
:
:T.Thank you for your quick reply.
:

: I would like to cut the line voltage down to 110 for these old radios instead of the 120 or so that we now have. Anybody have some ideas on how to do that?
:

: I would like to cut the line voltage down to 110 for these old radios instead of the 120 or so that we now have. Anybody have some ideas on how to do that?
:

This works well, is easy to build, and can be used with any of your vintage radios.
http://www2.faculty.sbc.edu/kgrimm/boatanchor/voltagereducer.htm

Hi Ross

You could use a bucking transformer. A 12 volt @ 1 amp filament transformer can drop the line voltage by this voltage. You don't need a high current transformer as only the secondary is in series with a radio. Unlike a resistor which depends on the load this method gives a stable voltage out.

Norm

: I would like to cut the line voltage down to 110 for these old radios instead of the 120 or so that we now have. Anybody have some ideas on how to do that?
:

The resistor was suggested as a per-radio use. If you plug all of your radios into the same outlet, or wish to supply all of your radios with a bucking transformer, that method will work as well.

T.

:The resistor was suggested as a per-radio use. If you plug all of your radios into the same outlet, or wish to supply all of your radios with a bucking transformer, that method will work as well.
:
:T.
: