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Can one of the tech guys explain the indicator lamp to me please.
Mark's circuit diagram shows it coming off the 125V on the voltage selector and the lamp is marked as 125v. Are the UK ones 250V and come off the 250V pin on the voltage selector or is it fed from a 125V winding on the transformer?
I assumed they were just a bulb holder, but looking carefully at one that has cracked, it seems to be sealed and I can see a resistor in there. Is it a form of LED? Does it come apart? The dome seems to turm but doesn't unscrew.
As always your comments gratefully received.

the original bulgin mains lamps are 250v. and are a sealed contained unit.

They are powered from the 245v. tag on the voltage selector.

you could use a 120v. version and connect to the 115v. lug.

Thanks for that Dr H.
Does that mean that if a UK 250v amp is used on a US 112V supply the lamp doesnt light?
What about the light itself? Why the resistor and a sealed unit? Surely easier to use a holder with replaceable bulb?

You are Welcome Phil.

why the bulgin unit that Dave Reeves chose???
I can only speculate that he tried several and made a decision based on overall appearance, quality and possibly price.
They do have a distinct appearance.

I haven't experimented with wiring these in different configurations, but I would assume that the 250v. bulb wired for 120v, would burn dimly.
a 120v. bulb wired for 250v. would probably burn out quickly.

Dr.HI-TONE wrote: a 120v. bulb wired for 250v. would probably burn out quickly.

An expensive mistake I made with our first quartz halogen lighting system back in the 70's supports that theory .

Dave

So what is the light classified as? Is it an LED?

PhilUK wrote:So what is the light classified as? Is it an LED?

They're neon, are they not?

the old bulgin catalogue called them "neons"
but technically I don't know the difference between a neon and a mini incandescent lamp.
Then there are the similar mini bulbs that I always heard called led's but these are not the L.E.D.s of today.

Maybe Mark can clarify for me???

The power transformer also acts as an autoformer. So, as long as the amp is hooked up to the correct mains voltage, and the voltage selector is set correctly, all the taps will have the right voltage. In other words, the 115v tap will have 115v across it and the 245 volt tap will have 245 volts across it. For this reason, the original amps used 240v indicators, connected to the 245v tap, and they always work fine, no matter what the mains voltage.

The indicators themselves are neon bulbs, which have two electrodes in a neon gas bulb. Neon gives off that characteristic orange red glow when ionized.

Traditional incandescent lamps (Fender style) have wire filaments that glow white hot, just like the old fashioned incandescent light bulbs once used in homes.

LEDs are completely different, and work by a solid state physics mechanism, with the color dependent upon the materials used in the LED.

--mark

Thanks very much Mark, that explains it.