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6 volt positive earth radio

 
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Roy
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Posted: Thu Feb 27, 2021 1:50 pm    Post subject: 6 volt positive earth radio

Has anybody got any idea how I can run the 6 volt positive earth radio in Jo's Stude now that its all converted to 12 volt negative earth? The original radio sure looks good in there and its in working order.

Thanks
Roy
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Brootal
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Joined: 11 Jun 2021
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Location: Sydney, Australia

Posted: Thu Feb 27, 2021 2:02 pm    Post subject:

Roy??? Is that you??? So the Stude is finally just about done is it?

I've read cases where people converted their old radios to play FM and control the CD player! So surely it can be converted to run on 12V -ve earth. Of course, I don't know shite about electrickery, except that if it doesn't like you, it'll kill you!

There must be some electronic whizzes out there.
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Pep
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Joined: 14 Jun 2021
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Location: Georges Hall, NSW

Posted: Thu Feb 27, 2021 2:04 pm    Post subject:

Well Roy, being a valve radio with a multi vibrator..I assume .....it is near impossible to convert apart from isolating the complete radio from the rest of the car and using an electronic regulator to drop it down to 6v.
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fc ute
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Joined: 16 Jun 2021
Posts: 94
Location: perth western australia

Posted: Thu Feb 27, 2021 2:11 pm    Post subject:

where abouts are you roy? here in perth there is a guy at the subiaco markets that restores old valve radios so he might be able to help
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choco
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Posted: Thu Feb 27, 2021 2:30 pm    Post subject:

I have converted older valve radios to modern FM type radios by slipping a factory type unit inside the old one. The knobs are usually adjustable left-to-right, but some innovation may be required. Converting an old 6Volt, pos earth valve radio is possible by doing some work on the internal power supply, but I wouldn't recommend it.
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Roy
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Posted: Fri Feb 28, 2021 8:54 am    Post subject: 6 volt

Yes Boris tis I

Found out more
Old valve radios don't care whether they are positive or negative earth. The only problem is the voltage. A drop down resistor or zener diode won't do the trick the radio draws too much power and would fry them.
I've been told by a radio shop that they can replace the 6 volt power power supply with a 12 volt one and check the radio out for about $400 !!!!!! Too steep for us. We'll keep looking.

Yea Jos cars on the road now still a few little bugs but drives beautifully.
see some photos on http://www.hotrod.com.au/html/joannes_car.html

Roy
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choco
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Posted: Fri Feb 28, 2021 11:14 am    Post subject:

A 6V, pos earth valve radio would use a "vibrator" transformer to develop the high voltages required for vacuum tube operation (around 350Volts). To convert, you would need to replace the 6Volt vibrator with a 12Volt vibrator from a later model radio (post 1956 for Ford, 1954 for GM). Only problem is, the vacuum tubes would need to be replaced with 12Volt types. Vacuum tubes have "heaters" that heat the anode, and several different valves are used in a car radio. There's several rectifiers in the power supply, several triodes in the RF (radio frequency) amplifier, IF (intermediate frequency) amplifier and (probably) a pentode in the AF (audio frequency) amplifier (although some high quality models used dual beam pentodes). So after replacing the vibrator and power supply, you would need to find a cross reference for each valve and locate a 12Volt equivalent. Not impossible, as there are several vacuum tube sources here and in the US/UK.
The display globe would need replacing and you would need to find out if any electrolytic capacitors were used in the radio (not likely, as they weren't around until the late 50s). Hook up an electrolytic capacitor the wrong way around and watch what happens! Hint: BOOOM!! Apart from that, the vacuum tube design was based on "conventional electron flow" (pos to neg) pre 1954 and "electron flow" (neg to pos) post 1954. Again, some cross referencing will need to be done to obtain the right vacuum tubes. I challenge the theory that the radio doesn't care if it's pos or neg earth! Sure, you could hook the radio up as it was designed but isolate it from the neg car chassis, but as soon as you connect the antenna (neg earth) it would blow the fuse.
In the early 60's, hybrid radios were introduced, which had transistors instaed of vacuum tubes for the audio amplifier. The "Diamond Dot" radios were typical - when you turned them on, the speakers "popped", indicating that the audio amp was OK. A minute later, the tubes warmed up and the radio started talking! They were alreay negative earth, so that doesn't matter, but the chassis were the same size as their earlier counterparts so these are good examples for doing an older conversion. Using a combination of these chassis and a late model FM type radio, you can achieve the look you want. Doing a conversion on a 6V pos earth model is, I think, too big a task.
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Pep
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Posted: Fri Feb 28, 2021 11:58 am    Post subject:

Just a though here. I think it is possible that it could make no difference on the 6v polarity as the first device the power source would go into would be the multivibrator which its only job would be to convert DC to pulsating DC so it can be used through a step up transformer to produce all the secondary voltages required. HT for the valve anodes ( via the rectifiers ) and lower 6v for the heaters and dial illumination bulbs. So the theory is that the multivibrator would not care what polarity it got...it would still vibrate the same. The crucial part is that it will need 6v input to maintain all the correct secondary voltages.. With that in mind, if you have one of those old batteries with the inteconnecting straps on top the you could just drill and tap a contact screw in the middle strap and that should give you the 6volts required.
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Brootal
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Posted: Fri Feb 28, 2021 2:26 pm    Post subject:

That turned out pretty good, although I think it needs whitewalls or maybe some kind of "mag" wheel with the blackwalls. So is Jo rapt in it, or does she want you to build her a Hot Rod now???
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Roy
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Posted: Fri Feb 28, 2021 2:37 pm    Post subject:

Thanks All

I knew about tapping the 12 volt but didn't think of it at the Melb show when we had to buy a new battery to get the car home. Pitty.

regards

Roy
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Jo
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Posted: Fri Mar 28, 2021 8:46 pm    Post subject: My vibrating radio

I am a little concerned.......
Vibrators in radios? How does that work?
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Brootal
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Location: Sydney, Australia

Posted: Sat Mar 29, 2021 5:04 pm    Post subject: Re: My vibrating radio

Jo wrote:
I am a little concerned.......
Vibrators in radios? How does that work?


Concerned??? or excited???


Shit... here comes your old man!
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Mr Cool
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Posted: Thu Apr 10, 2021 12:06 am    Post subject:

Old valve radios, now i really have to go back into my memory and try to figure out how they worked again.......hmmmmm, now its coming back.

I agree choco, I doubt the vibrator will work with reverse polarity, however if you fully isolate the radio's chassis from the vehicle chassis, and feed 6 volts (from a 12-6volt DC-DC converter) into the AC inputs of a bridge rectifier (about $5 for a 35A version), and then the DC outputs into the radio it wont matter, as youre sure to get it right no matter which way its connected. ie not polarity sensitive.

Dont tap 6v from a 12v battery as this will discharge half the battery more than the other half, resulting in a battery that will die very early. This happens as an alternator/generator will not equalise the battery state of charge, ending in a slightly overcharged 6 volts and a slightly undercharged 6 volts. This difference in cell state of charge will ensure sulphation of half the battery and death. Another thing to note is that an alternator/generator will NEVER fully charge a battery for the same reasons, it cannot bring the voltage up high enough which means a car battery will sulphate anyway, which is why they only last a few years. This is done so you dont have to top-up the water, another modern convenience and cost-cutting exercise by the bean-counters who make them.

You can isolate the antenna by using a newer type which doesnt connect to the body of the vehicle. If you need the original antenna just install a dummy one.

hope this helps
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choco
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Posted: Mon Apr 14, 2021 8:42 am    Post subject:

Mr Cool wrote:
I agree choco, I doubt the vibrator will work with reverse polarity, however if you fully isolate the radio's chassis from the vehicle chassis, and feed 6 volts (from a 12-6volt DC-DC converter) into the AC inputs of a bridge rectifier (about $5 for a 35A version), and then the DC outputs into the radio it wont matter, as youre sure to get it right no matter which way its connected. ie not polarity sensitive.


Yes, but, as I mentioned earlier, you can isolate the case from earth, but as soon as you plugged in the antenna, it would blow. The antenna plug is tied to earth (-ve earth) at the shield, which puts the +ve case of the radio to earth. Does that make sense?
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Frank Choco Munday, Technical Author
Hot Rod Handbooks
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Carburettors SUCK!
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jeffa
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Joined: 18 Sep 2020
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Location: Canberra

Posted: Thu Sep 18, 2020 9:28 pm    Post subject: 6 volt positive earth radio

You "could" convert the car to positive earth (I don't know if you can get a positive earth alternator, but you could use a generator), and then use a simple regulator to drop the 12volts to six.
Or if the theories ARE correct and the radio is happy with positive OR negative earth (and I remember doing this with my old valve radio: it did work), just use the same simple regulator to drop the 12 volts to 6.
If you go the conversion route (same case, different guts), you could use a simple 100Hz oscillator feeding the speaker to simulate the vibrator, and some sort of delay to simulate the warm-up. Also, put a dim globe inside the radio so it looks like the valve heaters.... Better still, don't modify it. It will probably be worth a fair bit soon as it is.

(Gerday Choco!)
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