Hi guys , I need to drop from 12 volt 5 amperes to 6 volt 5 amps without loosing the amperage?
How can I do that.

With AC, you can simply use a transformer. When you drop voltage with a transformer, amperage actually goes up, so you will have double the amperage available (a good thing) and half the voltage. With DC, you can either use a resistor or special circuitry. There aren't usually resistors commercially available for amperages this high. I assume that you are doing this in a car--say using a 6 volt radio in a 12 volt car. If you go to www.chevsofthe40s.com, you'll find voltage reducers specifically designed for tube type auto radios. As I said before, though, there is a fairly easy way to convert a 6 volt radio to 12 volts.

Thomas

If you purchase a voltage reducer for an auto radio, you want to purchase one of the high amperage ones (capable of 8 amperes or more), and you want it to be a regulated constant volts type. These are a bit expensive.

Thomas

Hi

If you are sure of 5 amps a 1.2 ohm @ 50 watt or greater resistor will work. Low value resistors used in transistor work should be available.

If current will vary a voltage regulator should be used to drop 12 to 6. LM338 regulator will handle 5 amps and is easy to use.

Norm

:If you purchase a voltage reducer for an auto radio, you want to purchase one of the high amperage ones (capable of 8 amperes or more), and you want it to be a regulated constant volts type. These are a bit expensive.
:
:Thomas

Thanks, well Yes Thomas is right Im trying to power up a 6 volt car radio with a D.C power supply but this unit is a 12 volt. I dont want to buy any expensive device because the radio is not mine and I only want to power it up to look if it its Ok.

Milton

:Hi
:
: If you are sure of 5 amps a 1.2 ohm @ 50 watt or greater resistor will work. Low value resistors used in transistor work should be available.
:
: If current will vary a voltage regulator should be used to drop 12 to 6. LM338 regulator will handle 5 amps and is easy to use.
:
:Norm
:
::If you purchase a voltage reducer for an auto radio, you want to purchase one of the high amperage ones (capable of 8 amperes or more), and you want it to be a regulated constant volts type. These are a bit expensive.
::
::Thomas

If you occasionally work with 6 volt automotive radios, a 6/12 volt battery charger usually works well. They are not too expensive, depending on which one you get. If you purchase a 6 ampere one (minimum required), radios that draw 7 or 8 amperes may trigger the circuit breaker every so often, causing the radio to cycle on and off. You can also purchase a 600 ampere 6 volt automotive battery at Batteries Plus for $45.00. You can use the battery for tests, and use the charger to keep the battery charged. This is a bit complicated, though. You are better off just purchasing a heavy duty 6 volt battery charger and leaving it at that. If you can get a 10 or 20 ampere charger, this will be ideal. They are readily available at most automotive stores.

As I said before, if you want to permanently convert a 6 volt automotive radio to 12 volts, change the tubes over to 12 volt tubes. If the radio uses an 0Z4 rectifier, this tube does not use a filament that is powered off of the supply, so you can leave it alone. It will work in both types of radios. A 6X5 rectifier, on the other hand, must be changed to a 12X5. Then, to convert the vibrator supply over to 12 volts, place a 10 to 20 watt resistor of low resistance (10 to 50 ohms should do it) in series with the supply. If the supply uses the chassis as the return wire, the voltage after the resistor measured across from the resistor to the chassis should be about 6.8 volts with the radio on (warmed up) and the engine at high idle. If you are using a solid state vibrator in the radio, be sure that it is of the proper polarity for the type of car you are using it in (positive or negative chassis). The vibrator must still be a 6 volt vibrator since it will be receiving 6 volts after the resistor you added, and the transformer that it operates is designed to run at 6 volts. If you are using an old mechanical vibrator of the non-synchronous type (rectifier tube in power supply), this type of vibrator is not normally sensitive to car polarity.

OH YEAH! Don't forget to change the pilot lamps to 12 volt bulbs.

Changing all the tubes over to 12 volt tubes can be expensive, so if you are just testing the radio for a friend, you are better off just using a battery charger.

Also, if the particular radio has no rectifier tube or solid state rectifier, but instead uses a synchronous vibrator, the wiring of the power transformer must be changed around if the radio is to be used with a polarity other than what it was originally intended for (again, positive or negative ground). If you run into this, ask me and I'll tell you what to do.

Anyway, converting a radio to 12 volts is fairly easy, and doesn't require some external transistorized device that can fry and accidently feed the radio a full 12 volts. Once you convert the radio, it's going to stay that way, and it won't cause you any trouble.

Thomas

:Thanks, well Yes Thomas is right Im trying to power up a 6 volt car radio with a D.C power supply but this unit is a 12 volt. I dont want to buy any expensive device because the radio is not mine and I only want to power it up to look if it its Ok.
:
:Milton
:
::Hi
::
:: If you are sure of 5 amps a 1.2 ohm @ 50 watt or greater resistor will work. Low value resistors used in transistor work should be available.
::
:: If current will vary a voltage regulator should be used to drop 12 to 6. LM338 regulator will handle 5 amps and is easy to use.
::
::Norm
::
:::If you purchase a voltage reducer for an auto radio, you want to purchase one of the high amperage ones (capable of 8 amperes or more), and you want it to be a regulated constant volts type. These are a bit expensive.
:::
:::Thomas

Another thing: if you are using a solid state vibrator in a radio that has been converted to 12 volts using a resistor in the vibrator supply, you may want to place a 1000 to 3000 MFD condenser (electrolytic) after the resistor from the resistor to the chassis of the radio. Some solid state vibrators may not work properly without this.

Thomas

:If you occasionally work with 6 volt automotive radios, a 6/12 volt battery charger usually works well. They are not too expensive, depending on which one you get. If you purchase a 6 ampere one (minimum required), radios that draw 7 or 8 amperes may trigger the circuit breaker every so often, causing the radio to cycle on and off. You can also purchase a 600 ampere 6 volt automotive battery at Batteries Plus for $45.00. You can use the battery for tests, and use the charger to keep the battery charged. This is a bit complicated, though. You are better off just purchasing a heavy duty 6 volt battery charger and leaving it at that. If you can get a 10 or 20 ampere charger, this will be ideal. They are readily available at most automotive stores.
:
:As I said before, if you want to permanently convert a 6 volt automotive radio to 12 volts, change the tubes over to 12 volt tubes. If the radio uses an 0Z4 rectifier, this tube does not use a filament that is powered off of the supply, so you can leave it alone. It will work in both types of radios. A 6X5 rectifier, on the other hand, must be changed to a 12X5. Then, to convert the vibrator supply over to 12 volts, place a 10 to 20 watt resistor of low resistance (10 to 50 ohms should do it) in series with the supply. If the supply uses the chassis as the return wire, the voltage after the resistor measured across from the resistor to the chassis should be about 6.8 volts with the radio on (warmed up) and the engine at high idle. If you are using a solid state vibrator in the radio, be sure that it is of the proper polarity for the type of car you are using it in (positive or negative chassis). The vibrator must still be a 6 volt vibrator since it will be receiving 6 volts after the resistor you added, and the transformer that it operates is designed to run at 6 volts. If you are using an old mechanical vibrator of the non-synchronous type (rectifier tube in power supply), this type of vibrator is not normally sensitive to car polarity.
:
:OH YEAH! Don't forget to change the pilot lamps to 12 volt bulbs.
:
:Changing all the tubes over to 12 volt tubes can be expensive, so if you are just testing the radio for a friend, you are better off just using a battery charger.
:
:Also, if the particular radio has no rectifier tube or solid state rectifier, but instead uses a synchronous vibrator, the wiring of the power transformer must be changed around if the radio is to be used with a polarity other than what it was originally intended for (again, positive or negative ground). If you run into this, ask me and I'll tell you what to do.
:
:Anyway, converting a radio to 12 volts is fairly easy, and doesn't require some external transistorized device that can fry and accidently feed the radio a full 12 volts. Once you convert the radio, it's going to stay that way, and it won't cause you any trouble.
:
:Thomas

Well, it looks like I have many options. yes I was considering the possibility of changing the 6 volt tubes to 12 volt and this is no big problem because all the tubes of this radio have theyr respective 12 volt counterparts 6X4, 12X4 6AQ5, 12AQ5 6AV6, 12AV6 6BE6, 12BE6 etc. the vibrator I have is an mechanical type but it is only for tests I need to order again a solid state one (because I blew up othe first) as the car is a 1955 Ford the electrical wiring is far away from the original one since originally it is positive ground and actually is negative ground. I am conscient that I need to order a negative ground solid state vibrator (probably in 12 volt) it depends on my friend. and of course the change of the negative pin wiring, accordingly with the new vibrator. But my doubt is if the circuit would work well once this changes were made.
PD the radio is a motorola 5MF8 but I have the schematics if you want to watch them.
Milton.

Well, if you run into trouble with the first method, you could use a 12 volt vibrator and then place an appropriate resistor in series with each end of the transformer primary to each corresponding connection on the vibrator. To choose the appropriate resistance, the vibrator should be removed. With a solid 12 volt power supply wired to the radio (12 volt battery at exactly 12 volts), connect one of the resistors directly to the power source, bypassing what would normally be the vibrator points if a mechanical vibrator was in place. Measure the voltage after the resistor to the center tap of the transformer. If a 12 volt battery is being used at exactly 12 volts, the voltage after the resistor should be exactly 6 volts. Repeat for the other side. Once finished, connect the resistors to the vibrator terminals where the transformer primary ends used to connect. This should allow you to use a 12 volt vibrator without feeding 12 volts to the transformer (which would fry both the transformer and the vibrator.

As for changing the polarity of a radio that uses a synchronous vibrator, I simply keep using the part of the vibrator that feeds the transformer primary, and then I take two diodes of proper rating and use them to construct a full wave rectifier for the secondary. I arrange them so that the secondary feeds the radio with proper B current polarity. Changing the radio to a solid state synchronous vibrator may prove more difficult, but probably will not.

Thomas