I get this question at least a half dozen times a week..."How come you don't have a reducer for my 6-volt radio? " The short answer is this..."Because of the amount of current your radio needs to work properly varies, due to things like to reception, sound level, and the voltage available (With the engine off less voltage will be delivered to the radio requiring more current from the battery as compared to engine running and generator output.
The voltage delivered to the radio can range between 5 volts and 7 volts. A voltage reducer has no way to compensate for that variance in incoming voltage. Most voltage reducers have a 40 percent error rate, and to a radio that is a lot.
The Details -
When the electrical load varies more than 10% that greatly affects the life of the vacuum tubes, and the parts inside of the radio itself. Your original 6-volt tube radio should never receive more than 8-volts... so if you are running an 8-volt battery your original radio will not be long for this world. That also goes for your dash gauges, bulbs, and anything else electrical.
Also keep in mind...that most voltage resistors are only about 50 % efficient. That means that when the voltage is reduced by half (from 12-volts down to 6 volts) the amperage output is also reduced by half.
In reality...that means that in order to get the 12 amps needed to start your radio, your electrical system would need to deliver 24 amps to the incoming side of the voltage reducer. Now after the radio warm up and it only requires 8 amps of current to function, the incoming electrical load changes to 16 amps of current.
That is a huge variation in the electrical load so what usually happens is the radio voltage reducer is designed for an average between the high and low voltage. Because of the 40 percent error rate and having no way to adjust for the range in voltage is what causes problems for your radio.
The other concern... is what happens with the heat generated as the voltage reducer scrubs off the excess current. Think of this as driving down the highway with the emergency brake on. The faster you drive the more heat that will be generated. A voltage drop for a radio is equal to about 50 mph. Things will get damn hot!
Despite the best advice... I still see voltage reducers advertised for original tube type radios. The people selling the voltage reducers clearly do not know how they work or about the fire hazard they represent!
Even if your radio survives the fluctuations in voltage, your car may not. The chances of your antique vehicle catching on fire from an overheated voltage reducer is very real. I have seen a half dozen antique vehicles over the years... catch fire and were destroyed from an overheated voltage regulator.
Imagine what would happen inside of your house if the voltage varied forty percent? Any type of voltage reducer that works off of resistance (which is about 90 percent of those sold for original tube type radios) will kill off your radio within the first year they are installed.
This type of voltage reducer has been around sine the 1970's.
And just so you know...it doesn't matter it the voltage reducer is encased in ceramic like the old school ones, or attached to a block of aluminum to serve as a heat sink... the end result will be the same!
This is a modern version of the old school ceramic voltage reducer.
By contrast, if you were to convert your original 6-volt radio to 12 volts, your radio would require just five amps to function. By converting your radio to 12 volts, solid state tubes, and vibrators can also be installed which will eliminate the warm up time. There are 12-volt tubes and vibrators available for most 6-volt radios. The radio would come on and play immediately just like a modern radio does today. In addition, features like FM can be added. The outside of the radio will look and function the same as it always did.
You can also get solid state rectifiers and leave the tube sockets empty (most of the time they will epoxy a washer over the tube sockets so nobody tries to replace the tubes) or they can change the rectifier socket to a mini and use a 12 x 4 rectifier.
They will also change the dial lights and make sure the outside of the case is marked 12 volts. That is a much more reliable and safer solution and one that will last for many years. You have a lot of options that come with your upgrade to 12-volts.
There are dozen of radio shops still around that can convert your original 6-volt radio to 12-volts and keep the original looks and function.
So...that is why I do not offer a voltage reducer for your radio and now that you know how they work, you know to stay away from them as well.