Just a query - UK Vintage Radio Repair and Restoration Discussion Forum

toshiba tony · 12th Jul 2021, 11:54 am

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.

12th Jul 2021, 12:02 pm

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.

Radio Wrangler · 12th Jul 2021, 12:28 pm

You'll find a lot of mains switches had only AC ratings (at 240v) and weren't considered safe to break DC.

David

toshiba tony · 12th Jul 2021, 12:56 pm

Thanks both of you, like the AC handling idea though.

Nuvistor · 12th Jul 2021, 1:17 pm

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.

ms660 · 12th Jul 2021, 1:26 pm

I remember the -ve heater sets, also the Thorn/BRC capacitor dropper sets and their "Cool Chassis" sets (Autotransformer)

Lawrence.

12th Jul 2021, 11:54 am	#1
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 978	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.

12th Jul 2021, 12:02 pm	#2
Guest Guest Posts: n/a	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.

12th Jul 2021, 12:28 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

12th Jul 2021, 12:56 pm	#4
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 978	Re: Just a query Thanks both of you, like the AC handling idea though.

12th Jul 2021, 1:17 pm	#5
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	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. __________________ Frank Last edited by Nuvistor; 12th Jul 2021 at 1:29 pm.

12th Jul 2021, 1:26 pm	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Just a query I remember the -ve heater sets, also the Thorn/BRC capacitor dropper sets and their "Cool Chassis" sets (Autotransformer) Lawrence.