Voltage Requirements For Vintage Radios

Many of my radios have a voltage requirement of 110 to 115 V AC. However my house voltage outlets are running at 123 V AC and I am concerned about causing any damage to some of my radios and I have been reluctant to plug in some of them for fear of causing any damage with the higher voltage. I'm wondering if there is a way to restrict the voltage to 115 V AC inside the chassis of some of these radios as I go about replacing the capacitors and restoring some of them. I recently purchased a Philco model Number 42-380 and it requires 115 V AC. I will be replacing the capacitors on this particular radio next month and wonder if there is a way to protect the radio from the excess voltage from the house voltage

Thank you in advance for any assistance you might recommend or suggest that would help me understand this better.

jgates

Mt. Prospect, IL USA

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Dear Joseph,

You can solve this matter using a bucking transformer.

Please see the attachment.

This cames from antiqueradios forum

Meyer

• Bucking transformer (35 KB)

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Hello Joseph,      To be on the safe side of thngs I use a variable transformer when firing up an older radio. I use it to slowly to bring up the voltage on a radio that has not been used in a long time. With radios that have been recapped I still use the variable transformer. I plug in a isolation transformer to the variable one and plug the radio into the isolation transformer.I do this especially with AC/DC sets. I generally run the voltage at about 100 - 105 volts to the radio. The radio will play and you will notice that it will run a little cooler. It's less wear and tear on the radio's tubes and transformer if it has one. If you run the radio on house current (120 volts) the transformer will heat up after about 15 minutes or so. The Atwater Kent radios of the late 20s that had their transformers imbedded in tar,and the tar would leak out when using 120 volt house current and begin to overheat. When all the tar leaked out it would burn up. The radio will play just fine at 100-105 volts. I have seen combination variable and isolation transformers on the market. That makes a good investment. But buying seperate ones will work just as well.  Hope this helps, Garrett

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Hi Garrett,

Thanks so much for the advice! I will invest in getting an isolation transformer and a variable one so I can protect my radios! I have a Stromberg-Carlson Breadbox or casket type radio and it runs so hot when I have ran it in the past but no more! Not without the setup you mentioned. 

Another member sent me a schematic for a Bucking Transformer from Radio Shack but I'm not sure just how to wire it up so I'm going to ask him for additional advice if he can help me.

I like your idea better though so I may just go with that but it's nice to have some options.

regards,

Joe Gates

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Dear Joseph,
I see that you have some difficulty in interpreting the diagram I sent in my other message.
I will try to explain better:
The old radios are designed to operate with a voltage between 100 and 115 volts.
Nowadays, as you know, we have in our electrical outlets a voltage between 120 and 130 volts.
The cheapest solution to obtain the old parameters of voltage is a "bucking transformer".
To do this setup, you only need a transformer with 125 volts or 127 volts on the primary and 12 volts on the secondary with the capacity to handle at least 3 amps.
Subtracting the 12 volt from the input voltage, you'll get 115 volts at the output of the set up.
See the new picture attached.
Note that you'll have to make a little experiment to connect properly the secondary wires.
Inverting point "a" with point "b", the output will be the sum of the mains voltage (127v) + the secondary voltage (12v). So we'll have 139 volts at the outlet.

I hope this cleared up any doubt.

Regards,

Meyer

• bucking 2 (22 KB)

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