Proper Speaker Ohms

[Dennis Detweiler]

The speaker in my 39 radio is shot. Does anyone know the proper ohm speaker required? I don't know if I will tackle the job of removing it and replacing it because of the wires and other parts that are threaded through the speaker frame. It looks like I'd have to take too much of the radio apart to remove and replace it. Likely just mount a speaker elsewhere behind the dash.

[garbagestate 44]

Most of those old speakers had 2 coils.The coil  (called the voice coil) glued to the cardboard form in the base of the cone is probably between 4 and 8 ohms. Back then,speaker magnets sucked so to get around that, they used electromagnets,often called field coil or electrodynamic speakers.For a car speaker they might range from a couple hundred ohms to a thousand.If you go with a modern speaker,you can pretty much ignore the field coil leads and just connect the voice coil leads. If you tried that on an AC set,the kind found in a home,you would cook something. As is always the case with vintage tube driven electronics be very careful as parts of the circuit can carry pretty respectable voltage. Don't ask me how I know.To figure out what you have,You might try this site, http://www.nostalgiaair.org/. They have thousands of schematics. There are lots of sites out there that you can extract useful info from before you start tinkering including do's and don'ts.Good luck.

[FlashBuddy]

Speakers are cheap. Start with an 8ohm and see how it sounds. Take you next step from what you learn there. Have any thrift stores around? They are rife with funky electronics. Buy a sack of speaker crap and give 'em a go. Keep the one that sounds best to your ears.

Edited December 23, 2017 by FlashBuddy
Typo

[Dennis Detweiler]

Sounds good.

I'm a musician and have done upgrades/mods to my solid state and tube amps for several years. I know with tube amps, there has to be a speaker load on the tubes or it overheats and can fry the tubes. Also, with tube amps, the proper impedance speaker is important to keep the tubes from running too hot. I assumed the same for a tube car radio, but maybe since DC is involved it's not so important? Most tube guitar amps use either a 4ohm or 8 ohm speaker and using anything above or below the recommended ohm's isn't recommended. Some amps have a selector switch on them.

I'll see if I can track down a schematic for the philco c-1608 radio.

[garbagestate 44]

With AC sets I think some guys use a filter choke that matches the output tube impedance and some people get big wirewound power resistors but they get hot.I have a Philco 802 and some years ago I needed a replacement speaker. I came across somebody on the internet who knew more about it than me. He said I could just leave the fc leads unattached and it would be good.I stole the permanent magnet speaker out of a junker 1949 Fada 790 (mainly because it fit the dash opening) and it works fine.

[37silverstreak]

On ‎12‎/‎23‎/‎2017 at 10:11 AM, Dennis Detweiler said:

Sounds good.

I'm a musician and have done upgrades/mods to my solid state and tube amps for several years. I know with tube amps, there has to be a speaker load on the tubes or it overheats and can fry the tubes. Also, with tube amps, the proper impedance speaker is important to keep the tubes from running too hot. I assumed the same for a tube car radio, but maybe since DC is involved it's not so important? Most tube guitar amps use either a 4ohm or 8 ohm speaker and using anything above or below the recommended ohm's isn't recommended. Some amps have a selector switch on them.

I'll see if I can track down a schematic for the philco c-1608 radio.

I'm restoring the radio in my '48 Plymouth which is a Philco C4608. It was missing the speaker but I was able to find an original one on Ebay . I'm not sure about a 1939 model but my radio uses a 4ohm voice coil and I think the field coil was about 3 ohms. You can use a P.M. style speaker, The field coil is only used to provide the magnetism for the voice coil. Most old home radios would utilize the field coil as part of the B+ power supply so you couldn't easily adapt those but it will work fine for an auto radio. Good luck!

Kevin