1930s field speaker?
 

Hi all.

New to the forum but thought I'd join as I have been bitten by the bug of valve equipment and speakers.

Recently acquired what I think is a field speaker. Poor condition but repairable. Tested it on a sinewave and sound is coming through which is good news.

It has Cambridge England stamped on connection box on rear. Can anyone provide any info on the speaker? Came across similar made by Kellogg's hope got that right.

I've attached photos.

Cheers, Chris

Re: 1930s field speaker?
 

Looks Very PYE

That transformer is a PYE type.

It will be early 1930 give or take a year or two I would Guess.

Cheers

Mike T

Re: 1930s field speaker?
 

Cambridge is indeed the home of Pye.

Re: 1930s field speaker?
 

I imagine the reference to Kelloggs is to Rice & Kellogg ca 1925 who developed the modern type dynamic loudspeaker. ( Not the cereal manufacturer ).

Re: 1930s field speaker?
 

thanks for info guys.
Yes it is pye stamped on it ew called look ha.
Any ideas on model? Be good to have some background info on it for restoration. Not sure if it came out of a radio or was in speaker cabinet.
So this is a field speaker and quite rare. Or just a run of the mill job as they say. Not been able to find same anywhere.
I'll treat the cone as it's still in pretty good shape the outer is knackered looks like leather or faux leather. Not sure where to source that.
The weight is phenomenal for its size no wonder it's on a solid teak box.
Cheers Chris

Re: 1930s field speaker?
 

I don't see any connections for a field coil? Looks more like a permanent magnet speaker with an output transformer attached to me?

Re: 1930s field speaker?
 

Post #37 of this thread gives a few hints as to how I repaired a similar vintage speaker, using ripstop nylon.
https://golbornevintageradio.co.uk/f...d.php?tid=6616

Mike

Re: 1930s field speaker?
 

Would there be any value in looking at those repair kits sold for replacing the foam surrounds on 1980s speakers?

Re: 1930s field speaker?
 

I'd agree.

If it only has one winding, it's a permanent magnet speaker, and certainly looks like one.

If it were a mains energised speaker with a field coil, unless unrectified HT was applied to the field coil - basically an electro-magnet - applying say a sine wave to the speech coil or the primary of the output transformer would produce no sound from the speaker. A mains energised speaker has three coils - the field coil, usually about 2,000 Ohms of fine wire (as often as not, by now open circuit), a 'hum bucking coil' (a fraction of an Ohm) in antiphase to cancel out the hum created by the field winding, and the speech coil (voice coil) maybe two or three Ohms. (The field coil also acted as a smoothing choke).

Before the war, it was difficult to produce permanent magnets powerful enough to be used in loudspeakers so an electromagnet was used. Basically, a large coil around a pole piece. Advances during the war in materials and production techniques meant that after the war, quite small yet powerful permanent magnets could be produced, which simplified speakers, made them more reliable and much less costly to produce.

The speaker in question looks to me like a permanent magnet speaker with a large magnet, with the output transformer attached. If it is indeed a field coil mains energised speaker it will have three windings as shown in the part circuit below of an Ekco AC77.

Second pic shows the field coil and him bucking coil.
Third pic shows the pole piece onto which the filed coil is fitted.
Fourth pic shows a rewound field coil reassembled onto the refurbished speaker.

Re: 1930s field speaker?
 

I think that in the mid 1930's many sets had field coils. My father's RGD 625 ( 1936 ) had a Rola 10" field coil speaker. The HMV & Marconiphone sets he had ( 1937 models ) had permanent magnet 13" x 8" elliptical units. In the radio components cupboard was a Whitely Electrical 10" "Stentorian" unit which had its own matching transformer bolted to the frame There was an integral selector switch for a number of impedance settings.

Re: 1930s field speaker?
 

Re my recent post about the RGD Rola speaker. In later years I always puzzled as to why such speakers did not produce violent 50 or 100Hz hum. Your circuit diagram has solved that for me

Re: 1930s field speaker?
 

In theory, a non energised field coil speaker will not produce any sound.

However there is usually some residual magnetism in the field coil laminations, and a weak sound can be heard.

Field coil speakers were popular in mains powered equipment.

Permanent magnet speakers were almost essential in battery powered sets.

Re: 1930s field speaker?
 

lovely job on the speaker re-build, it looks fantastic.

Re: 1930s field speaker?
 

Thanks. (20,000 turns, 2.3kM of wire!).

I didn't mean to hi-jack the thread, but to differentiate mains energised speakers, which are in effect, electro-magnets, from permanent magnet speakers. When field coils fail, as they so often did/do, it wasn't uncommon for repairers to scrap the mains energised speakers and fit a PM one instead, and in place of the field coil, to fit a smoothing choke (or even a resistor) across the reservoir & smoothing caps for HT continuity and smoothing.

Post-war - even if a replacement field coil for an ageing set could still be obtained from the set-maker - the cost, including labour for dismantling and reassembling the speaker on maybe a ten year old set would have been prohibitive. As hobbyist restorers, labour costs are an irrelevance if we have the time, skill and inclination to do whatever is called for.

Re: 1930s field speaker?
 

Sorry that should have been post #27 in my thread on the KB 214 https://golbornevintageradio.co.uk/f...d.php?tid=6616

Mike

Re: 1930s field speaker?
 

That's a hugely helpful diagram from G4EBT - thanks. I am trying to revive a Defiant MSH 971AC which, aged 16, I originally bought in a church auction for 5 shillings. I used to listen to Radio Northsea and a bit of short wave with an external BFO. Anyway the whole speaker side is connected to the chassis via a bundle of wire on an octal plug which has complicated things somewhat but it appears that the speaker transformer primary is open circuit which explains why there is no HT on the output valve anode. The field coil and humbucker check ok. The output valve is a Mazda PEN45DD. Would any old output transformer that I can scrounge do as a replacement?

Re: 1930s field speaker?
 

Hi guys lots of info here have not visited for a while.
Lovely job on that speaker a true love for restoration is evident there.
So does anyone know where, or what the speaker I have is? Definitely Pye and I managed to get a faint sound with volume full up on my valve receiver but like I say very faint.

The magnet is massive and the speaker weighs a ton. I do have two battery radios a marconi and Telsen both of which I got working well hissing and usual tunning meowing type of noise no stations unfortunately. I had some batteries made up and had to us a dc input regulator to get the 2 volt the speaker worked on these straight off the HT.

I also managed to source some soft leather and redo the surround although not very happy with it colour is same as original but it just looks wrong well not pretty but I'd assume this would have been in a cabinet?

Suppose after all that is it rare as I cannot find anything similar, would it have been housed in a cabinet or came housed in a large radio cabinet? date poss 1930? would it have been for the domestic or commercial use, any background info would be great.
Pic attached of speaker and the telsen radio I fully refurbed which I managed to get some noise out of.

Cheers

Re: 1930s field speaker?
 

A 1929 Selectron radio I have has Pye transformers of this design so I suspect this part would date from 1929-1933 or so.

The speaker is an odd one as most speakers of that period used field coils, for example the HMV 540AC speaker has a similar leather surround to yours. If you hadn't said it was Pye, I would have guessed Philips as they made some large permanent magnet speakers.

You should be able to pick up something on that radio as long as you have a decent length aerial. Did it come like that as the layout could be improved as the RF valve is a bit close to the detector and a bit of HT decoupling would do not harm.

Re: 1930s field speaker?
 

Thanks for info.
Yes that's the actual layout of the radio as sold think it was in the wireless mag 1930. There was a kit design as well
so I have the schematics. Yeah good idea could have a play around with the design. Did not think of that at the time.
I'm in middle of refurbing a quad qc2 pre amp once done I'll have a mess around with the Telsen. Hopefully the batteries still have some charge left in them.

Cheers

Re: 1930s field speaker?
 

Lack of sound from the speaker could be a tired permanent magnet-big problem or it could be the voice coil- big problem or it could be sticking / off centre voice coil- probably fixable or a fault in the drive to it- probably fixable.

Have you checked the voice coil resistance? Should be just a few ohms.

Have you tried driving the speaker from an independent, known good source?