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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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13th Nov 2007, 2:43 pm | #1 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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1920's horn resuscitation
The first project in my coil winding therapy programme, this needed a repaint which took longer than expected. It's still not perfect and I have tried 3 different primer layers to try to get the paint to stabalise on the aluminium and old paint but it still has a few not quite black areas.
Mentioned in another thread, both coils were open circuit. I measured the resistance of the wire and the height of 50 turns and looked it up in Langfords to determine it was standard copper 46SWG. An estimate of the average length of a turn and the knowledge it would have been 1K ohms per coil it was easy enough to determine the number of turns. I threw together a winder/counter jig and fully rewound one coil but only needed to replace part of the second. I've not seen other horns in the flesh but this is a monster standing 25 inches tall with a 14 inch diameter opening. The base is cast iron and has a bore in which fits an inverted cast cup holding the coils. The knob on the front moves the cup in the bore allowing the gap to the diaphragm to be adjusted for different DC currents. As received the cup was solid in the bore and to free it took 30 minutes of blow torching with water in the cup to reduce expansion and liberal sprays of penetrating oil which caught fire. The construction is otherwise the same as vintage headphones just on a grander scale with a 3 inch diaphragm held in place by a chrome plated 0.5Kg lump of brass which also supports the steel and spun aluminium horn. Probably now working as well as it ever has, this is from the early 1920's, bright emitter valves and enthusiastic hobbyists period...to be honest, despite the exceptional build quality, the performance is rubbish and the technology was quickly replaced by paper cones but that's not the point! It had the shadows from lost labels on the bottom lip of the opening and has no other makers mark. It's been suggested it's a Fellows Volutone but if you know better please let me know...Peter |
13th Nov 2007, 3:25 pm | #2 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,806
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Re: 1920's horn resuscitation
Looks a fantastic job Peter . I just love these "mechanically challenging" restorations. What looks like the impossible to start with gradually bears fruit. Well done.
Neil
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preserving the recent past, for the distant future. |
13th Nov 2007, 3:36 pm | #3 |
Heptode
Join Date: Apr 2006
Location: Indianapolis, Indiana, USA.
Posts: 674
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Re: 1920's horn resuscitation
What a difference!
So, what are you going to hitch it to?
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Just playing with high voltage.... |
14th Nov 2007, 1:23 am | #4 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: 1920's horn resuscitation
I was thinking of adding an ipod dock...:
Lots of headphones and horn speakers seem to have survived from the early 20's but few crystal and early valve radios are left to drive them...I would guess that most were crude home built sets that have long since been thrown away. So the answer is I don't have anything that early although I have a working 1931 ST400 kit that uses PM series valves but I'd need to watch the output current as the horn will only take 8mA. |