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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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12th Jul 2021, 11:54 am | #1 |
Heptode
Join Date: May 2006
Location: Accrington, Lancashire, UK.
Posts: 978
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Just a query
Why were most b\w sets in the 60's AC only? Was it because the heaters were normaly fed with a negative voltage, I remember some sets of this age had voltage selectors on but when was the national grid optimised at 240v, if there is a really simple answer I apologise but I have dementia and try as I might nothing springs to mind, thanks anyone.
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12th Jul 2021, 12:02 pm | #2 |
Guest
Posts: n/a
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Re: Just a query
I guess two reasons, one the smaller ones may have had transformers and you get a higher HT with AC, the peak of the waveform.
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12th Jul 2021, 12:28 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,903
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Re: Just a query
You'll find a lot of mains switches had only AC ratings (at 240v) and weren't considered safe to break DC.
David
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12th Jul 2021, 12:56 pm | #4 |
Heptode
Join Date: May 2006
Location: Accrington, Lancashire, UK.
Posts: 978
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Re: Just a query
Thanks both of you, like the AC handling idea though.
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12th Jul 2021, 1:17 pm | #5 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: Just a query
I believe you have the answer with the heaters being fed from half mains through a rectifier. I have checked Ekco and Bush sets from the change over to negative heaters. The sets before the change Ekco T433 are AC/DC T441 AC only, similar the Bush TV125 AC/DC, TV135 AC only. Both AC only models have rectified heater supplies. The Bush models used the same On/Off switch ganged with the volume control.
Other sets may well have had transformers Full or Auto, which would have made them AC only. I think the AC only switches came a little later with CTV sets. As an aside, those Volume control/Switches used in the Bush sets were I think made by Morganite, RS sold the identical control, the carbon track was a moulded piece of carbon not just a coating of carbon and the slider contact was also carbon. I had the occasional switch failure but never a noisy volume control.
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12th Jul 2021, 1:26 pm | #6 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Just a query
I remember the -ve heater sets, also the Thorn/BRC capacitor dropper sets and their "Cool Chassis" sets (Autotransformer)
Lawrence. |