1936 Radio and a 12 to 6 converter

[SuperDave]

The instructions that came with the converter says that you cannot use the original 6 volt Pos. Gnd. radio. on 6 volts neg. Gnd. Is that so?
I don't want to let any smoke out of the radio! It's a 1936..

[V8COOPMAN]

Radios can be VERY "polarity" sensitive. I would heed the warning and leave the smoke where it belongs! DD

[flatheadmurre]

And an old tuberadio draws a lot of current so you need a sturdy converter !

[gearhead1952]

If the radio still has the mechanical vibrator then no problem running it on neg ground. I have done it. Tubes don't care but solid state electronics do.

[rotorwrench]

The modern solid state voltage converters (converts direct current to pulsating direct current for voltage manipulation) are polarity sensitive. These were starting to show up in the mid 50s while 6-volt systems were still in use. The old vibrators aren't polarity sensitive. There might be polarity problems with the electromagnetic speakers though but they can be converted to modern speakers with permanent magnets. It always depends on whether a radio has ever been updated from the old type vibrator to a solid state type or what year, make, and model it's from.

I've never had a reason to change the polarity. If I did, I'd be changing to 12-volts and plan on using 12-volt components.

[blucar]

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In 1958 I bought a '55 Pontiac 2dr sdn. The car did not have a radio or a heater/defroster. The car had a V8 and an auto trans, very low mileage. I bought the car because the price was under $900. out the door, the dealer was very motivated to sell it because is was a plane Jane car. I had just gotten out of the Army, my wife was pregnant with our first child and we were broke.
I had a nice 6v radio out of a '37 Chevy, (Pos ground) a friend was junking the car, I kept the radio.
I bought a GIZMO called VOLT-A-DROP, 12v to 6v at Pep Boys, modified the stock radio delete panel in the dash, installed the '37 radio with the stock speaker in the center of the firewall. The radio worked great for over three years. In 1962 I ran across a '56 Pontiac radio in a wrecking yard, I removed the "37, put it away in the garage.
In about 1980 a friend of mine bought a '38 Chevy, no radio, I sold him my '37 radio for $350., he was happy as could be. I told him to have it check out before he had it installed, it checked out fine except for a weak vibrator tube.

[V8COOPMAN]

Originally Posted by blucar

In 1958 I bought a '55 Pontiac 2dr sdn.
I had a nice 6v radio out of a '37 Chevy, (Pos ground) a friend was junking the car, I kept the radio.
I bought a GIZMO called VOLT-A-DROP, 12v to 6v at Pep Boys, modified the stock radio delete panel in the dash, installed the '37 radio with the stock speaker in the center of the firewall. The radio worked great for over three years. In 1962 I ran across a '56 Pontiac radio in a wrecking yard, I removed the "37, put it away in the garage.

Blucar.......You might want to check again. Chevies were never POSITIVE Grounded. Some GMCs were, but NOT Chevy! DD

[SuperDave]

Thanks guys. I will check the vibrator. I bought my first car in 1956..A 31 model A with pos. gnd. I bought a 47 Plymouth radio from a junk yard. Bolted it in on the drivers side of the steering wheel. Hooked it up and it worked fine. I am pretty sure the 47 Plymouth was neg. gnd.
Will report back when I find out!

[blucar]

The majority of the early Mopars, (DCPD) were positive ground... I have a '48 Dodge which is positive ground..

[SuperDave]

Originally Posted by blucar

The majority of the early Mopars, (DCPD) were positive ground... I have a '48 Dodge which is positive ground..

Maybe I got lucky !! LOL

Today I took the radio out to check it out. (not much fun), It had a mechanical vibrator and a schematic pasted inside. On the schematic, the input was labeled 6 VDC + or -. So it should work with either Pos. or neg. gnd. It doesn't work, but doesn't blow fuses and no smoke! LOL I'll keep trying.

[rotorwrench]

If you can hear the vibrator hum then it is likely just fine. The most common problems with those old radio sets besides the occasional burned out tube rectifier, was the old capacitors. They will sometimes pop like pop corn. They aren't hard to replace if your soldering skills are up to date. Deteriorated speakers would be the next item but changing to a permanent magnet speaker is not a real difficult mod. Turnswitch has modern replacements. There are more than a few folks out there that modify them for an MP3 player hook up or modern 12-volt AM/FM guts so that they can be used on a regular basis again. There is not much activity in the AM band any more. A person can go all day with an MP3 and save all the commercials & talk shows.

[SuperDave]

I thought I would report the final results. The short story is...It WORKS!
The radio is going into an open car and has had a PM speaker mounted in the cabinet. The external plug-in harness that came with will not be used. There is an under running board antenna. No antenna trimmer adjustment on the radio, soo I will find out how that will work.
The vibrator was stuck. I removed the cover and "unstuck" the points. That vibrator was not listed as a proper replacement. The buffer cap has been recently replaced. It does work fine on the bench, but once in a while I have to "thump" the vibrator to get it moving again. I found a proper N.O.S. vibrator "on line", it is on it's way from Ohio. The experts say that the buffer circuitry is different on many radios and the vibrator must be matched to the buffer circuit. The only exception would be if you use a solid state vibrator, which I am not going to do. I put a meter in the power line and found the radio uses 4.9 to 5.0 amps while running. So the 15 Amp converter should work fine. The only other drain is the oil pressure and fuel gauges. Milliamps? I rewired the dial light to turn on and off with the radio rather than with the dash lights. That might alert the driver that the radio is on..

[jimTN]

I was told recently that the old vib.with points can be fixed by filing the points. It was a old time radio man who was working on one of my radios with that type of vib. that told me about it.

[BillM]

I modified a mechanical vibrator years ago by removing all the innards and replacing them with a couple of diodes and a small resistor. The details are probably on the web somewhere. It will be polarity sensitive but you could wire it to match whichever ground polarity you have.

On second thought the diodes were a substitute for a rectifier tube (OZ4 ?) not the vibrator.

[Overkill-F1]

Originally Posted by jimTN

I was told recently that the old vib.with points can be fixed by filing the points. It was a old time radio man who was working on one of my radios with that type of vib. that told me about it.

I have repaired contacts with a strip of 600 wet/dry and folded it over a feeler gauge. Spray the wet/dry sandpaper with contact cleaner and work it back and forth holding the contacts closed on the sandpaper.
Works well unless the contacts are really worn out.
...Terry

[SuperDave]

I never mentioned the model of the radio. It is a Philco FT-6. used in 1935-36 Fords.

[Paul Bennett]

It is possible to operate an original 6v car radio directly on 12v without regard to polarity and no step down device. The 6v tubes can all be replaced with a 12v tube. Example a 6V6 - a popular output tube - can be directly replaced with a 12V6. The first number is the filament voltage and all tubes have a 12 equivalent. Next step, the vibrator whose job is to produces a few hundred volts for the tubes to operate with. The vibrator circuit will not like operating at double it's normal voltage. So a schematic of the radio and some smarts to modify the voltage into the vibrator circuit is necessary.

Sorry to leave you hanging without a 'how-to' on this last point but I did want to point out the practicality of using a 6v radio on 12v with a current of less than 1/2 compared with using a 12v>6v converter.

Another feasible modification after changing tubes is disabling the 1 or 2 tube output stage and substituting a transistor amplifier module. Net result is a radio rivaling the power draw of modern car radios. Alternatively one could extract the vibrator circuitry with a simple inverter to produce 150v for the radios tubes.

This thread started me thinking. I'm not interested in restarting my engineering career but pointing out what can be done fairly easily. It's a shame I gave away my dad's stock of several hundred tubes, never thought they would be needed again. My dad (1907-1959) had a radio-tv repair shop in the '50s and I grew up on car radios.

Excuse my reminiscing. But that's what having an old car does to me.

[rotorwrench]

I remember my Pop taking the old 51 Merc to the radio shop on several occasions in our local small Kansas town. Just about every little town had a radio/TV shop back then. The radio set would have been a bear to get out from under the dash but the bottom cover was easily removable so you could get to the plug in items easier for service in the car.

It's nice to get one of the old sets to work but a person does have to keep in mind that it may need regular maintenance. They were excellent amplifiers which makes the a good candidate for an MP3 addition since there usefulness comes back that way. I can see why a lot of folks get them converted to a modern AM/FM set so they don't have to mess with them anymore as long as the modern components are good quality. Little tiny boards on a great big radio chassis makes the kind of a big empty box but at least it looks original from the outside.

[Marvin/TN]

Check with Charles Forgey at 423-344-8357 or 423-785-6333 in Harrison TN. I can convert it for you.