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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 23rd Jul 2018, 7:58 pm   #21
bionicmerlin
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Default Re: A vintage screw-base low voltage bulb holder

These were used in their 100s by the BBC in the Dr Who exhibition at Longleat.
The ones in use was made by Radio Spares and had a rivet in the centre. The rivet often gave up and the whole thing came lose or gave up. My father used to replace them during maintenance and bring the old ones home .We used to drill the rivet out and put a small nut and bolt in its place to use as projects at home when I was a young boy. I still have some in front of me now .
Andy
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Old 23rd Jul 2018, 11:00 pm   #22
Herald1360
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Default Re: A vintage screw-base low voltage bulb holder

6BA cheesehead ISTR did the job.
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Old 24th Jul 2018, 6:22 pm   #23
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Default Re: A vintage screw-base low voltage bulb holder

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Originally Posted by Refugee View Post
I can remember when I was at school we nabbed a white one of those bulb holders to try out a small neon bulb we had found and identified as being a "mains" bulb.
It didn't have a built in resistor as we found out...
You really had me amused at that!
Within very recent years a friend of the museum at Dulwich [who should have known better] plugged in a small SBC neon lamp into the bench distribution board. It didn't have a resistor....

Blinding flash and total shock on the face of the guilty party. We all collapsed with laughter!

Yes those mini batten holders bring back happy memories. It gave me great delight to receive one to replace the twisted wire and rubberized insulation tape connections but I was around 6 years of age.

A long time ago, another age. John.
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Old 24th Jul 2018, 9:07 pm   #24
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Default Re: A vintage screw-base low voltage bulb holder

Yes, they go off with quite a bang
Are they marked as 200-250V or similar, despite the lack of resistor?
There must be something that made us think 'mains'.
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Old 24th Jul 2018, 10:43 pm   #25
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Default Re: A vintage screw-base low voltage bulb holder

The most amazing thing about those Bikelite LED bulbs to me is that they work down to 1volt of either polarity! Dunno how they do that

Stuart
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Old 25th Jul 2018, 1:39 am   #26
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Default Re: A vintage screw-base low voltage bulb holder

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Originally Posted by dseymo1 View Post
Yes, they go off with quite a bang
Are they marked as 200-250V or similar, despite the lack of resistor?
There must be something that made us think 'mains'.
The one we did at school went like a Victorian photo flash but with less smoke.
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Old 25th Jul 2018, 2:28 am   #27
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Default Re: A vintage screw-base low voltage bulb holder

If you search the Internet for "Joule Thief", you will find plenty of circuits for lighting an LED from a single 1V5 cell. It's basically a simple blocking oscillator using a coil wound on a ferrite bead, and the striking voltage for the LED is obtained from the back EMF in the coil. It will continue to run as long as the cell voltage is still sufficient to turn on a transistor (though the cell can actually reach a point where it is still just running, but there is not enough voltage for the oscillator to restart if it is disconnected and reconnected).

The same device is also known as a "Vampire torch", because it sucks every last drop of life out of a 1.5 volt cell.
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Old 25th Jul 2018, 9:07 am   #28
stuarth
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Default Re: A vintage screw-base low voltage bulb holder

Yes, I’ve built several Joule thief circuits, but they do care about battery polarity, the Bikelite bulbs don’t.

Stuart
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Old 25th Jul 2018, 10:24 am   #29
Herald1360
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Default Re: A vintage screw-base low voltage bulb holder

Maybe the Bikelite bulbs' Joule Thieves use symmetrical FETs and inverse parallel LEDs?

Or maybe an active bridge rectifier on the input using MOSFETs- you can do interesting stuff with a custom IC in very little space.

Someone'll probably know......
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