Typical speaker for 1931 Marconi 246? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

AC/HL · 19th Jun 2016, 3:29 pm

Here's one, but it was probably intended for high power use, such as cinemas: http://www.lowthervoigtmuseum.org.uk/voigtdrivers.html

Mike. Watterson · 19th Jun 2016, 4:45 pm

Quote:

Originally Posted by pwdrive

Mystery solved, DC mains not AC mains

Yes, that will work!

I've not seen (even on "paper") a domestic external speaker using a field coil. I'd imagine the magnet would be cheaper. The Field coil / Electrodynamic / Energised speaker existed on mains powered sets as you replaced an expensive magnet with a cheap coil. The power supply was already there, "free". As a bonus you could save on an HT choke. None of that applies for an extension speaker, they would have used the drive units made for battery sets.

Quote:

Originally Posted by AC/HL

Here's one, but it was probably intended for high power use, such as cinemas

Again, "mains energised" is a bit misleading. It used DC, so AC mains required a PSU.

ms660 · 19th Jun 2016, 4:58 pm

I haven't found one either, trawled loudspeakers on Radiomuseum from 1925 to 1935, the only advantage I can think of would be that a dedicated rectifier PSU could provide more field coil current than the usual "in the receiver" set up could.

Lawrence.

ms660 · 19th Jun 2016, 6:32 pm

Seems to be a few field coil loudspeakers (not in cabinets) with on board rectifiers made over the pond, one uses a Jensen M60 loudspeaker which has a handle fitted to it...transportable.

Lawrence.

AC/HL · 19th Jun 2016, 11:58 pm

I think the DC is assumed, AC obviously won't work. The early ones were a stop gap until more powerful magnets were developed. The sort we are familiar with were also a later development, but the "mains" prefix survived. Even now you see that, where the correct term is just "Energised". One illustration here refers to twin rectifiers (obviously American) and the other lists the field coil voltages of the Voigt speaker. Neither are domestic models though.

Mike. Watterson · 20th Jun 2016, 8:19 am

Quote:

Originally Posted by AC/HL

I think the DC is assumed, AC obviously won't work. The early ones were a stop gap until more powerful magnets were developed.

Cost too, the magnets had to be cheaper than a coil.

19th Jun 2016, 3:29 pm	#21
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Typical speaker for 1931 Marconi 246? Here's one, but it was probably intended for high power use, such as cinemas: http://www.lowthervoigtmuseum.org.uk/voigtdrivers.html

19th Jun 2016, 4:58 pm	#23
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Typical speaker for 1931 Marconi 246? I haven't found one either, trawled loudspeakers on Radiomuseum from 1925 to 1935, the only advantage I can think of would be that a dedicated rectifier PSU could provide more field coil current than the usual "in the receiver" set up could. Lawrence.

19th Jun 2016, 6:32 pm	#24
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Typical speaker for 1931 Marconi 246? Seems to be a few field coil loudspeakers (not in cabinets) with on board rectifiers made over the pond, one uses a Jensen M60 loudspeaker which has a handle fitted to it...transportable. Lawrence. Last edited by ms660; 19th Jun 2016 at 6:42 pm. Reason: correction

19th Jun 2016, 11:58 pm	#25
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Typical speaker for 1931 Marconi 246? I think the DC is assumed, AC obviously won't work. The early ones were a stop gap until more powerful magnets were developed. The sort we are familiar with were also a later development, but the "mains" prefix survived. Even now you see that, where the correct term is just "Energised". One illustration here refers to twin rectifiers (obviously American) and the other lists the field coil voltages of the Voigt speaker. Neither are domestic models though. Attached Thumbnails