Wayne Parham Messages: 18751 Registered: January 2001
Illuminati (33rd Degree)
Tube radios usually have speakers with a field coil rather than a fixed magnet. You could replace a field-coil speaker with a fixed-magnet speaker, but then you would need to add a choke in place of the field coil. The field coil serves dual purpose, as an electromagnet to interact with the speaker's voice coil and also as a power supply ripple filter.
I don't think many people care to know about tube radio speakers, but it is just something I've noticed when working with speakers that old. The effect that humidity and temperature have on modern speakers is the same, because their cones are made of the same stuff. So that's why I brought it up. You will see the same degradation of a loudspeaker purchased today as you would of a speaker purchased 100 years ago, if it is put in a hostile environment. For example, put a speaker in a car and leave it exposed to direct sunlight. It won't take long before the cone becomes brittle and tears. Covering the speaker cone with a grille helps a great deal, and keeping the car in a garage extends its life even more.
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