Sourcing a field coil speaker...

[jeyurkon]

Originally Posted by Reece

Use any PM 6 or 8" speaker that you have. The two remaining wires from the transformer go to the two terminals on the speaker. Polarity does not matter in this case. The transformer is fine mounted where it is.

The transformer is used because the tube has a high output impedance. The transformer matches this to the low impedance of the speaker. Ideally your speaker should be rated 3.2 ohms (commonly referred to as 4 ohms) but an 8 ohm will also work, just giving slightly lower volume, but probably not noticeable. This is a pretty hefty radio, power transformer and all, and was surely worth restoring. Congrats!

Reece

I learned something too. Thanks for clearing up when permanent magnet speakers started to be commonly used.

I'm not sure if titanstats caught your comment about all three wires going to the transformer. I take it that this is a push-pull output stage.

Do you have any suggestions for him on how to identify which lead goes to the center tap? That is if it's not still connected. Was there a generally accepted color code for this?

John