16-10-2021, 05:28 PM
Higher current hence fewer turns of thicker wire for same field. Or shunt it with a choke as a test.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
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A modded Cossor 54
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17-10-2021, 07:46 AM
(16-10-2021, 03:12 PM)`FRANK.C Wrote: The TV would have been originally have been fitted with energised speaker and at some point it failed and was replaced with a permanent magnet type. The choke was us ed to take the place of the energising coil. Hi Frank Looking at some of the other photos of 54s they appear to have a choke mounted on the loudspeaker too. The schematic doesn't appear to indicate the use of an energised speaker. I wonder if the speaker in your 54 is not in fact correct? Peter.
Hi Peter
You could well be right. The speaker does look the right vintage. The choke that was there wasn't original as it was crudely mounted. Though it is possible that there was another one there originally. I am just going on some photos that I found that suggests an energised speaker. This one from Radiomuseum has what looks like a energised speaker. This underside view from Brian Cuff's restoration on VRAT also looks to have an energising coil. Frank
19-10-2021, 07:37 AM
Quite a low valve count for its time. I just wonder how sensitive the RF stages were without the extra amp was?
19-10-2021, 12:16 PM
Hi Adam
Thanks for the ads. I note on one there is a strap from the mu-metal shield to the front panel. I haven't seen this on any other photo. Hi Trevor Yes, with just 13 valves in the basic unit it must be one of the simplest TVs ever produced. I am going to rewind the energising coil in the speaker. The original coil is wound with 0.125mm wire. I have some 0.19mm but I don't it is quite thick enough. So I have some 0.22mm ordered from RS. Frank
20-10-2021, 09:31 AM
Frank sorry I'm a bit late but in the original Blueprints from Cossor the circuit shows the choke as a 400 ohm field coil so I think it would be safe to say they used an energised coil speaker. Yours has been modded with PM speaker and separate choke.
Please see the picture attached. Chris
20-10-2021, 11:50 AM
Hi Chris
You are not late at all. Information like this is never too late. Thanks for confirming that it is a energised speaker. It is great to get that confirmed as now I know that I am heading down the right tracks. Frank
20-10-2021, 06:44 PM
This evening I finished the speaker.
I wound the coil with 0.22 mm ECW. I was able to fit 9000 turns on the former. This fill the former completely. Very short clip of the winding in progress here. After assembling back in the speaker the coil measures 527 R and 8.7 H. The resistance is a little too much but is a good starting point. When I get the set working I will try it out and see what te HT is like. While I was waiting for the wire to arrive I removed the rust and gave it a lick of paint Frank |
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