Handling the Voltage Multiplier Issues with High Line Voltage and Vintage Radios

What is “normal” household line voltage?

What is acceptable to our Vintage Radios?

Without getting into a deep discussion the voltage delivered to the average American home has gone up since the pre-WWII’s 110vac, then post-war 117vac is now 120vac.

The current standards are:

Yet our old radios might be intended for less.

My two Collin’s S-Line Stations definitely were intended for a bit lower voltage than 120vac.

Inside the S-Line components voltage can be multiplied to produce Vacuum Tube level voltages by step-up transformers.

If the original design took say 110vac and upped it to 800vac, it is a 7.273 multiplier.  (The 800vac is just a value I picked, as there are several stepped-up voltages in use in a S-Line station.)

If modern power is suddenly say the maximum allowable of 120vac  plus 6% for 127.2vac, the 7.273 step-up transformer is pushing out 925vac, which may be above the maximum safe voltage for a particular application.  Even a 120vac line voltage will he 873vac after the step-up.

What the Collins designer originally really wanted was that 800vac voltage they designed for, which would mean we have to figure out a way to limit the line voltage to 110vac.

Well you cannot call up your power company, as ask them to “turn my voltage down for me, guys” That isn’t going to get you anywhere.

Here is the solution:

Actually what is in those boxes are these:

Medium Duty Variac Transformers where we can “dial down” the output voltage to that ideal 110vac area.

The capacity (2KVA) is sized to handle a 516F2 power supply and 30L1 amp, and the build quality is solid enough to do shack duty with ease.

I bought these from an eBay seller, though the identical units were also available on Amazon, with the 16% Amazon cut added to them of course.

Each S-Line setup is getting its own unit.  The third is for other projects.

73

Steve
K9ZW

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One thought on “Handling the Voltage Multiplier Issues with High Line Voltage and Vintage Radios

  1. Bob W says:

    Don’t forget that those Variac clones are autoformers, no separate primary and secondary. So they would do fine for adjusting the voltage going into your radios, but they won’t give any isolation for people working on AC/DC radios like my ancient Hallicrafters S38-D.

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