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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 8th Nov 2019, 1:06 pm   #21
dave walsh
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
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Default Re: 1930s field speaker?

I like the thoughtful way in which you mounted this "ex-cabinet" LS Chris! Unless I'm seriously mistaken, the consensus seems to be that it's actually a permanenat magnet type-in which case what happens when you wave a screw driver at it?
I've always known that early speakers often had their own power source. I only came across the designation "Mains Energised Loudspeaker" though, not "Field" but [of course] the electro-magnetic creates one! It's certainly a fine example either way but given the vintage and "ad hock" production regime at the time, you may never locate it's original home. Based on past experience though, just me saying that, in the way of things, may result in a positive ID from a member

Dave W

Last edited by dave walsh; 8th Nov 2019 at 1:15 pm.
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Old 8th Nov 2019, 8:26 pm   #22
Join Date: Apr 2019
Location: Birchington, Kent, UK.
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Default Re: 1930s field speaker?

I have another a Houston type e 1930 loudspeaker pic attached that reads 1k on winding and the pye around 600ohm. If your saying there should only be a few ohms then something must be wrong then although I thought these 1930 and pre needed a higher output because of the design of radios back then. Just stabbing in the dark.

But if your saying should only be a few ohmes then obviously something wrong?

Any info on those readings most welcome.
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Old 9th Nov 2019, 1:18 am   #23
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Default Re: 1930s field speaker?

"Mains energised" has always struck me as rather a misleading term- the field coil has to be energised with dc, direct mains would be useless! You can get away with a fair amount of ripple voltage since the high inductance of the field coil means that the actual ripple current in the winding is quite low.
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Old 11th Nov 2019, 1:45 am   #24
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Default Re: 1930s field speaker?

It's one of those hangovers from earlier times. As David mentioned earlier on, the only way to get the field strength early on was an electromagnet. Originally they had a dedicated mains powered supply, but domestic versions usually used the HT current, and for economy it doubled as the HT choke. Alternatively, some were wired across the HT instead. Either way, they're energised. The mains bit is a lingering memory, nothing more.

Academic really, as this thread is apparently about an early PM speaker.
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