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Electromagnetic Speaker Replacement - Printable Version

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Electromagnetic Speaker Replacement - NV3G - 01-21-2009

I am working on a Philco Model 89 Code 123 with a shorted field winding in the electromagnetic speaker.

What is the proper procedure to replace the electromagnetic speaker with a permanent magnetic speaker?

Also, what circuitry is needed to replace the field coil?

Thank you.
Oscar
nv3g

Re: Electromagnetic Speaker Replacement - Terry Burns - 01-23-2009

Hi Oscar,
Looks to me like a 20 to 25 watt power resistor would work. The schematic shows the coil at 1125 ohms. A 1200 to 1350 ohm would work nice. Just lift the wires that go to the field coil and insert the resistor in an area that is away from any other components. Just beware it will get hot. If you get a slight hum you can increase the size of your filter capacitors by a little to remove the hum. You can still use the same audio transformer from your old speaker.

Just for grins you might peel all of the paper off of the coil and see if you have a bad connection where wires are tied together. You've got nothing to lose.

Terry

Re: Electromagnetic Speaker Replacement - NV3G - 01-27-2009

Terry

Thank you for the suggestion. I volunteer at the Bowie Antique Radio and Television Museum on Fridays for 4 hours. I repair radios and ask the owners to make a donation to the museum. I do not charge for my services. I am retired and enjoy working on the older tube radios.

I see that your from Marion, Illinois. I am originally from Kewanee, Illinois.

Take care and Best Wishes.

Oscar -

Re: Electromagnetic Speaker Replacement - Texasrocker - 01-27-2009

I have found that 10-watt wirewound ceramic resistors are more than adequate in replacing field-coils. They take up less space, & I have never had one fail yet in many of my sets that I play on a regular basis after many,many hrs of service. The 10-watters run abit warmer, but hold just fine. They can be mounted on terminal-strips in spaces where extra room is at a premium. However, if you have the extra space, the 20 watters run abit cooler. In some cases, a 10-watter can be soldered directly across the old spkr 4-pin chassis/spkr connector underneath the chassis, and will be hidden, allowing use of the old spkr wire harness. Just make sure the wires are cut that originally used the old field-coil. Just my .02 Icon_wink

Re: Electromagnetic Speaker Replacement - NV3G - 01-30-2009

I volunteer at the Radio and Television museum in Bowie, Maryland. I got back to the Philco 89 code 123. I replaced the field winding with an 1100 ohm high wattage resistor, added a permanent speaker and the radio is playing. I will probably add a choke coil for filtering. I need to check the alignment.

Thanks to Terry and Texas Rocker for their suggestions.

It appears that the field winding shorted out. It was black in the outer layer of the windings. Appreciate all of you help and suggestions.

Oscar
nv3g

Re: Electromagnetic Speaker Replacement - AI2V - 01-30-2009

I've always used a cheap garden variety 8 hy choke from Radio Daze to replace the original choke; I keep a supply available just for that purpose. They are small enough to fit in the underside of most any chassis. Any increase in B+ has never been enough to worry about.