# 12 to 6V/15A voltage regulator

#### Fer870

Joined Mar 10, 2020
4
Hello guys, new member here, i'm looking for a voltage regulator circuit, which i can use to mount an old 6V radio on a 12V car.

The requirements are:
Output voltage: 6.3V
Average current (from the radio's manual/schematic): 5.5A
Maximum current (based on the fuse used by the radio): 15A

I've researched a bit, but the circuits i found either couldn't keep with 15A loads, or when brought up were mentioned as "bad designs"

#### tinker123

Joined Mar 6, 2020
15

#### gerty

Joined Aug 30, 2007
1,277
First make sure the 6v radio isn't positive ground, some are and some aren't...

#### Fer870

Joined Mar 10, 2020
4
I've been looking into something similar and there is a sample circuit here: https://www.eleccircuit.com/high-power-supply-regulater-0-30v-20a-by-lm338/
Thanks, i'll take a look

hi 870,
Welcome to AAC,
Use a 12vdc to 6vdc 5amp buck converter, more efficient than linear types.
A while ago i looked into buck converters, but couldn't find one that handled the current. Now i can find a few rated for (depending on the model) 6-8A continuous, and 10-12A max (with a cooler). My question is, since the radio would be most of the time at 5.5A with 15A being the maximum peak, would i be ok with using a converter like the ones i mentioned?

First make sure the 6v radio isn't positive ground, some are and some aren't...
I'm looking into that. I believe it is indeed positive ground, but some people say that since it uses a vibrator in the power supply, the input polarity doesn't matter, while others say i should just replace the vibrator to change the polarity

#### atferrari

Joined Jan 6, 2004
3,930
What radio is that? 5.5 A is a lot of current.

#### Dodgydave

Joined Jun 22, 2012
9,090
Must be a Valve Radio then, the vibrator is for the HV for the Anodes...
You can replace it with a mini buck booster..

#### crutschow

Joined Mar 14, 2008
24,749
My question is, since the radio would be most of the time at 5.5A with 15A being the maximum peak, would i be ok with using a converter like the ones i mentioned?
I think the 6-8A converter would be sufficient.
It's unlikely to get above that current if the average is 5.5A.

#### crutschow

Joined Mar 14, 2008
24,749
What radio is that? 5.5 A is a lot of current.
33W is probably typical for a tube radio.

#### schmitt trigger

Joined Jul 12, 2010
202
It used a mechanical vibrator to step up the 6 volt to the high voltage anode supply with a transformer.
The tube's heaters were fed directly from the 6 volts.

So nothing should be damaged if you invert the polarity.

#### Fer870

Joined Mar 10, 2020
4
What radio is that? 5.5 A is a lot of current.
33W is probably typical for a tube radio.
Must be a Valve Radio then, the vibrator is for the HV for the Anodes...
You can replace it with a mini buck booster..
Yes, it's a valve radio- 1949 Automatic M-90

Dodgydave, i don't think it's possible to replace it. the power supply goes vibrator-transformer-rectifier. Did you mean replacing them all with a 6.3V DC to B+ DC booster? (i still need 6.3V for the valve heaters)
I think the 6-8A converter would be sufficient.
It's unlikely to get above that current if the average is 5.5A.
Ok, i think the buck converters are the way to go then

I'm looking into that. I believe it is indeed positive ground, but some people say that since it uses a vibrator in the power supply, the input polarity doesn't matter, while others say i should just replace the vibrator to change the polarity
I remembered now, this radio was on my grandfather's truck, which has a 12V negative ground system (the battery was tapped to supply 6V). If it worked back then, it means the radio doesn't care about polarity. i just need the regulator because i can't tap modern sealed batteries...
(As i was writing this message, schmitt trigger posted his, confirming my suspicions)

#### Dodgydave

Joined Jun 22, 2012
9,090
Yes, it's a valve radio- 1949 Automatic M-90

Dodgydave, i don't think it's possible to replace it. the power supply goes vibrator-transformer-rectifier. Did you mean replacing them all with a 6.3V DC to B+ DC booster? (i still need 6.3V for the valve heaters)

Ok, i think the buck converters are the way to go then

I remembered now, this radio was on my grandfather's truck, which has a 12V negative ground system (the battery was tapped to supply 6V). If it worked back then, it means the radio doesn't care about polarity. i just need the regulator because i can't tap modern sealed batteries...
(As i was writing this message, schmitt trigger posted his, confirming my suspicions)
I remember these had two twin triode valves, with 6.3V heaters, the ht is around 200V, a simple royer oscillator will do for the HT supply instead of that buzzing pesky vibrator..

#### Fer870

Joined Mar 10, 2020
4
I remember these had two twin triode valves, with 6.3V heaters, the ht is around 200V, a simple royer oscillator will do for the HT supply instead of that buzzing pesky vibrator..
Well, looking at the voltage chart below, the rectifier puts out 265V, so i could replace the vibrator( 6V DC to 6V pulsated DC), transformer(6V Pulsated to 300V AC), and rectifier(300V AC to 265V DC), with a single 6-265V DC/DC device. i will look into the royer oscillator you mentioned.

If it wasn't for the 6.3V tube heaters, i could simply use a 12-265V step up and connect the radio directly to the car. I know i could replace the tube for their 12V equivalents, but a complete tube swap costs ~3 times more than a converter...