Obsolete Fluorescent tube?

[DerbyBorn]

I don't need one but was just wondering what happened to the tubes that used to have a metallic strip along their length. Also - I recall that some starters had 4 pins. Why?

[Brian Gaff]

You know I have no idea about either, but I do remember some lights having strips, might have been to attempt to stop that wiggling line effect some tubes have when first put on in a cold room.

All I know about starters is that they are n just basically bimetal strip switches to try to get the tube to strike then remove that extra kick from the inductive part of the circuit. Maybe some double tube fittings had two in one housing? Brian

[DerbyBorn]

"Brian Gaff" wrote in news:nttl9r$qh$ [e-mail]:

I am thinking back to a Church Hall I helped to care for. It had old 5ft tubes with bayonet caps on the end. I eventually helped to fit adaptors for bi-pin and the new tubes sometimes had a metal strip. Not sure if they needed it.

[tabbypurr]

Aided starting with some ballasts. disappeared decades ago

For the heating element in thermal starters.

NT

[Andy Burns]

In think Mr Flameport has one in his recent youtube video

I never saw any tubes with bayonet ends though

[Mike Tomlinson]

En el artículo , Andy Burns escribió:

I did, when I was a kid. We had one in the garage, and at school the hall had them in the ceiling fittings which were waaay high. Well and truly dates me, I suppose :)

[tabbypurr]

A shop I know has one still in service. Probably has a PCB filled capacitor too.

NT

[Andrew Gabriel]

My parents still have two in their loft. A builder broke one a few years ago, but fortunately I found a spare tube elsewhere in the loft.

Fluorescent tubes started off with bayonet connectors in this country. The first commercial size in the UK was the 5' 80W tube. It used the same ballast as an 80W mercury vapour lamp and same lamp holders as regular filament lamps, so no new parts were needed to roll these out during WWII. This was not an ideal power rating from the efficieny point of view, and 5' tubes were dropped to 65W in 1960, and switched to bi-pin which all the newer tubes were using by then. In practice, all the 5' tubes produced during 1960s/1970s were dual rated 65/80W, and you could buy bi-pin to bayonet cap adapters, to fit them in older fittings.

(In the US, the first tube size was the 18" 15W 1" diameter tube, probably due to their lower mains voltage.)

[Andrew Gabriel]

They were used with quickstart and rapidstart control gear, when mounted away from grounded metalwork. These two control gear types vanished quite quickly because they were expensive, just to avoid the flashing at startup. Semi-resonant start replaced them, and didn't need the earth strip because it starts the tube with twice mains voltage across it. They can still be found on special tubes designed for low temperature starting, supplied for use in large commercial freezers and the like.

BTW, it wasn't just an earthed strip - the whole tube had a (very slightly) conductive coating, which the strip made the connection to from the metalic edge on the end connectors.

The very first starters (before glow starters were invented) used a thermal element. They died out quickly because they were slow to start and unreliable, so most 4-pin starters actually just have a glow starter in them, and the other two pins shorted together.

[harry]

Four pin starters have a bi-metallic srip and a resistor to make it work. Two pin starters are worked by corona discharge in a near vacuum tube.

The metal strip on the tube was to aid starting; it was earthed via a contact on the lampholders.

[harry]

Yes,I remember them in our local barbers shop in the early fifties. They t ook a minute or two to start ISTR.

[Zephirum]

They were in use in the drawing offices at work until the early 70's or thereabouts.

[tabbypurr]

Having used them they aren't slow and they're much more reliable than glowstarters. The reason for their demise was the constant 1w power draw, plus their inability to restart if switched off very briefly.

NT

[tabbypurr]

took a minute or two to start ISTR.

then they were very knackered.

NT

[DerbyBorn]

Andy Burns wrote in news:e6fc5lFn9ldU1 @mid.individual.net:

Thanks - I like his stuff. Will go and make some toast and then watch it.

[DerbyBorn]

DerbyBorn wrote in news:XnsA6A362A58BD57TrainJPlantntlworldc@81.171.92.236:

A great video - complete with the bayonet caps! The mention of the voltage selector on the Choke brought back memories of having once fitted a plug, you also had to set the voltage selector on many items.

[Mike Tomlinson]

En el artículo , Andrew Gabriel escribió:

Pic of those adapters here:

[DerbyBorn]

Mike Tomlinson wrote in news:nV $ [e-mail]:

It is said tha the bayonet was used because they were already manufactured. Did other countries go straight to the bi-pin?

[harry]

Back then, there were multiple voltages around the country. Some places even ran on DC.

Prewar, electricity often came from local factories, mines etc.

[Mike Tomlinson]

En el artículo , DerbyBorn escribió:

I'm not sure, not quite old enough to know :)

It seems to me likely that the bayonet was chosen as it was a known and proven design. Putting Edison screws on the ends wouldn't have worked - if you rotated the tube to fit one end the other would unscrew.