Voltage question.

[Lindsay Morris]

I think that Siemens and other makers used the hefty power resistor technique so that they could use the 100/110V lamps rather than use a 220/240V lamp as the lamp filament is almost twice as thick as the same lamp for 220/240V use.
That makes them less susceptible to filament damage by mechanical shocks and far less likely to blow at switch on as 220/40v lamps tend to do.

When its cold a lamp is almost a short circuit until it heats up in that fraction of a second it takes to light up.

I have one of the same model (Sound version) and its quite a good room warmer on cold nights!!!! The same machine is also very handy if your mains voltage is a bit low or a bit higher than normal you can adjust the lamp current to optimum for best light by adjusting the resistor knob either way until screen light is best and not over bright.

They DO run very hot and my lamphouse cover is now very discoloured due to the heat. Good machines in their day but no match now for a 250W Xenon Elmo !!

[Terry Sills]

Steve is the man when it comes to electronics. I am fortunate in that I have a Variac 10amp transformer, which I acquired at a local boot market for a few pounds. I always power my projectors through it and gently bring the voltage up to the correct power. I'm sure this increases lamp life significantly by reducing the shock of initial full voltage to the filament. I can easily bring the lamp up from a glow to full power which must be beneficial, certainly on the older machines.

[Maurice Leakey]

Lindsay is right.
The lower voltage filaments gave a much better light concentration, which in turn provided a much brighter picture than a mains voltage lamp.


Maurice

[Brian Fretwell]

Yes the more compact filament of low voltage lamps helps the optics focus the light on the gate and onward to the lens, also the reason 24v lamps could replace 1000w ones in projectors (slide and 16mm cine).

I think that the DC shock feels worse because AC tends to throw you off the contact due to muscle convulsions, DC freezes the muscle more and you make contact for longer.

[Dominique De Bast]

A lot of intersting informations. Thanks, everybody !

[Martin Jones]

Bit late in the day.......just an observation regarding DC mains supplies in the UK.
When I abandoned my job in Industry and went self employed as a TV and Radio Serviceman in 1971 there was still an area of Reading in Berkshire with DC mains. UK TV sets at he time worked happily on either AC or DC.

[Lee Mannering]

If my Dad was around he would have chatted to you for hours about that Martin. When TV started he helped out in a photo shop which started stocking TV's a very long time ago. He never lost his interest in it and when we had all those 70's power cuts Dad connected the farms tractor/lorry batteries to a transformer in the front room. Wonderful memories especially when the old Fergie wouldn't start next day.

[Maurice Leakey]

[QUOTE=.....Dad connected the farms tractor/lorry batteries to a transformer [/QUOTE]


DC connected to a transformer?
Are you sure, Lee?


Maurice

[Brian Fretwell]

Maybe a rotary converter. That would "transform" low voltage DC to AC I believe some London "Pirate" radio stations used them in the 60's-70's to transmit from fields in the days they used valve transmitters on Medium Wave.

[Steve Klare]

I have the modern equivalent, solid state of course!

True story: We had a power failure the other night. -maybe 30 seconds. With the two deep cycle batteries I have I could have kept the first floor lit and entertained maybe 4 nights.

I was almost dissapointed when the lights came on again!

About a year ago someone here imported a US spec projector to the UK and was having trouble getting past the difference in frequency. This would actually solve that problem. (It's just a matter of how much you want to solve it!)
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