Electromagnetic and high impedance speakers
 

Did you ever encountered radios with this kind of speakers? (maybe some tv sets used them too). Electromagnetic where the ones that didn't had a magnet, but a electromagnet in stad (not to be confuses with alsmost the same principle, but that had "funnel", like in old cartoons).
The high impedance ones (700-800 Ohms) where made so it will be no need of a audio output transformer (which needs to be of good qualty if you want a good sound)... dizavantage: the coild wire was thin and could get broke.

Yep, My Philco 42-380 has one, it's called a field coil speaker. Has an electromagnet instead of a permanent magnet. Otherwise it works like a normal speaker. I think it's low impedance though, because it has an output transformer.

I'm not sure about high impedance speakers though, if you're measuring the field coil instead of the voice coil you might see 800 ohms

If your talking high impedance voice coil they weren't common here in the US. A few of the early paper cone speakers in the 20's were high impedance but by roughly 1930 radios usually had built in low impedance speakers and they usually had a field coil (used as a B+ choke) instead of a permanent magnet.

One oddball case of a high impedance voice coil PM speaker in a US product is one of the car radios (IIRC it was Motorola) for the Chevrolet Corvair. It used a 40 ohm voice coil speaker. I know because a friend owns a Corvair and had to switch radios because that speaker was bad and he couldn't source one.

Post-war high impedance speakers where normal, not field coil. But like onto antother place, people dindn't understood that I asked 2 separate questions. :)
mr_rye89 , how does the speakers sounds :)

It sounds pretty decent, surprisingly good high frequency response, probably comparable with other decent radios made in 1941-42. My 1950 Zenith has a similar speaker but with a permanent AlNiCo magnet and it sounds similar.

Ditto to what Tom said, high impedance speakers are rare here.

FWIW my oldest radio (Philco 624 - 1936 version) has a permanent magnet speaker but it is a battery operated set.

Hi to all,
Hi TeleColor 3007,

800 Ohm impedance speakers were used in Philips radios circa 1960.
Many were in the BX series, very wide and low height models. Many had Stereo amplifiers for Phono but not FM Stereo.

These are very nice radios but if you are unlucky enough to find one with a dead speaker, spare speakers are absolutely impossible to find now.

Some collectors have published successful modifications to convert the audio output stage to transformer operation and repair the radio.

Best Regards
jhalphen
Paris/France

Hello. But how it was the sound on them?