Field coil speaker question

[superdog]

I picked up an old Silvertone fm tube unit that was I believe pulled from an old console for free off CL.It is working with a field coil wire speaker.The field coil wire speaker has three speaker wire and I wanted to connect to an EV Regency for mono use.How do I go about adapting it for that purpose?

 

[rrago]

I don't see a field coil, I see a permanent magnet. The three wires could be a center-tapped transformer??

 

[battradio]

Can you show a beter photo of the back of the speaker ,from what i can tell it looks like a PM speaker with the output transformer on the back .If the output transformer is on the back of the speaker ,disconect the two wires going to the voice coil and solder them to your speaker wires .

Mark

 

[superdog]

I don't see a field coil, I see a permanent magnet. The three wires could be a center-tapped transformer??

I am not too familiar with these but I believe it is a field coil.You just can't see it in the pics.These are the CL photos as I am unable to post my own.It has a three prong harness from the back of the unit leading to three wires blue,brown and red connected to the field coil section on the back of the speaker.

 

[JBL GUY]

I am not too familiar with these but I believe it is a field coil.You just can't see it in the pics.These are the CL photos as I am unable to post my own.It has a three prong harness from the back of the unit leading to three wires blue,brown and red connected to the field coil section on the back of the speaker.

In general the term "field coil" as applied to audio gear and speakers in particular refers to a coil on the speaker that does what the speaker magnet does.

Instead of having a permanent magnet it has a coil of wire that usually has the B+ voltage from the amplifier flowing though it and at the same time functions as a filter choke for the B+ voltage...

Your speaker clearly has a permanent magnet...So no field coil.

With out seeing the "coil" that is mounted on the speaker it is hard to say exactly...I would guess what you are seeing is the output/matching transformer...Just mounted on the speaker...

Unless the speaker itself is an unusual impedance you should be able to connect disconnect the wires that go to the voice coil and connect those wires to a different speaker...If possible that speaker should be close the same impedance as the original speaker...

The picture shows a speaker with a "field coil" in place of the "permanent magnet" that you can see in the picture that you posted...and a transformer mounted on the speaker frame...Most likely the output or matching transformer.

When you replace your speaker with the EV speaker you can remove the transformer from the original speaker and just connect to the EV speaker.

If once you get it...If the configuration is different let us know and post some pictures.

 

[cubby01]

Superdog, The pictures and your description has me believing it's a push pull amp section and the output transformer just happens to be mounted on the speaker. Probably blue, brown, red (center tap) on the amp side and green, black on the speaker side. Not uncommon.

 

[superdog]

I think I get it now.The field coil I am thinking of is the transformer.So is the transformer necessary to play the amp or can I just use a regular speaker.Which wire do I leave out.Thanks.

 

[battradio]

The transformer is needed ,you can remove the transformer from the speaker it is mounted on an conect it to a lager speaker .

Mark

 

[mashaffer]

If I am understanding correctly you have a PP amp with OPT mounted to the speaker. Three wires come from the amp (B+, output tube1, output tube 2) which connect to the transformer. Then you will either have two wire going from the transformer to the speakers voice coil connection or one wire to the speaker basket and the other to the plus speaker connection.

With the set turned off and unplugged. disconnect the wires from the speaker voice coil and connect them to another speaker. Leave the three wires from the set alone. Of course you will want to remove the OPT from the now unused speaker. Best bet is to measure the voice coil DC resistance on the existing speaker (assuming it is not blown) to get an idea of the impedance you are shooting for in the replacement speaker.

This is of course assuming I have followed this correctly.

mike

 

[mashaffer]

P.S. Primary on that OPT carries lethal voltages!

mike

 

[superdog]

P.S. Primary on that OPT carries lethal voltages!

mike

Thanks for the info.I was not aware of that.

 

[Sam Cogley]

Thanks for the info.I was not aware of that.

Tube gear can carry a nasty shock. From what I hear, it wasn't too uncommon in the old days for someone to kill themselves while working on a car radio in the car.