100 years of BBC - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

HamishBoxer · 24th Nov 2022, 6:38 pm

The "Knife Switch" looked like a knife blade and was ceramic base and used to earth aerials in thunderstorms etc.

Of course some were indeed used to switch power, a bit lethal depending on voltage across it!

G6Tanuki · 24th Nov 2022, 6:51 pm

Yes, the usual Knife-switch was a ceramic- or Bakelite-based beastie, looking like a miniature version of what you might see in Dr. Frankenstein's Laboratory.

"More Power, Igor!! More Power!!"

There were 2 kinds - one a simple 1-way version, you wired the antenna to one side and the other side to earth, so when the switch was closed they were shorted together and any static charges picked up by the antenna were drained away to earth.

The other kind was a 2-way switch; you connected the antenna to the centre, then one of the outer terminals went to the radio, the other to earth.

You had to remember to throw the switch.... not much good if you usually had it in 'radio' mode and the thunderstorm arrived while you were out at work!

Attached photo shows the second type.

Radio Wrangler · 24th Nov 2022, 9:57 pm

note the asymmetric clearance distances of the switch in the photo above.

Radio goes to the left, Earth to the right. antenna to the centre.

David

24th Nov 2022, 6:38 pm	#21
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: 100 years of BBC The "Knife Switch" looked like a knife blade and was ceramic base and used to earth aerials in thunderstorms etc. Of course some were indeed used to switch power, a bit lethal depending on voltage across it! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

24th Nov 2022, 6:51 pm	#22
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: 100 years of BBC Yes, the usual Knife-switch was a ceramic- or Bakelite-based beastie, looking like a miniature version of what you might see in Dr. Frankenstein's Laboratory. "More Power, Igor!! More Power!!" There were 2 kinds - one a simple 1-way version, you wired the antenna to one side and the other side to earth, so when the switch was closed they were shorted together and any static charges picked up by the antenna were drained away to earth. The other kind was a 2-way switch; you connected the antenna to the centre, then one of the outer terminals went to the radio, the other to earth. You had to remember to throw the switch.... not much good if you usually had it in 'radio' mode and the thunderstorm arrived while you were out at work! Attached photo shows the second type. Attached Thumbnails __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

24th Nov 2022, 9:57 pm	#23
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,880	Re: 100 years of BBC note the asymmetric clearance distances of the switch in the photo above. Radio goes to the left, Earth to the right. antenna to the centre. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done