Beseler Color Head question

I have Beseler 45 with the color head, and I've just scarfed up a nicer timer than my current one.

My old timer has a plug socket for the enlarger and one for the safelight, and I use both as designed. But the new timer has only one outlet for the enlarger.

I believe that the plug going to the Color Head does NOT actually supply power to the lamp in the unit, but rather supplies signal and some electronic circuit actually powers up the bulb. Is this correct? After all, the light head stays on even when the lamp is extinguished.

What I want to do is just use a small double pole relay from the timer, and alternate the power between the safelight and the enlarger based on the timer. But if I've got to supply the entire load for the lamp, then an icecube relay isn't going to carry the load. But if all I'm supplying is signal I should be OK. The safe light is 15 watts, so for 120VAC that's a small enough load to switch with just a small relay.

Does anyone know about the internal workings of this color head?

Thanks,
Michael

michaelbsc said:

I believe that the plug going to the Color Head does NOT actually supply power to the lamp in the unit, but rather supplies signal and some electronic circuit actually powers up the bulb. Is this correct? After all, the light head stays on even when the lamp is extinguished.

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The bulb has to get power somewhere, is there another power cord going into the head?

I don't have that head, but from what I understand on some Minolta/Beseler color 45 heads there are 2 cords, both of which supply 120V. One cord is for the 120V fan only, the other is for the 120V power supply for the bulb. I suspect that the power supply is a 'switching' power supply, where a triac rapidly turns the sine wave on-and-off so that exactly 82V are present at the bulb. In order for the laws of conservation of energy to be satisfied, any relay to the lamp circuit needs to carry the same wattage as the bulb. If it is a 200w bulb, you need a relay rated at 200W or about 2.3 amps.

The easiest solution would be to just get a timer that has another safelight socket. Timers are relatively cheap and sometimes free.

ic-racer said:

The bulb has to get power somewhere, is there another power cord going into the head?

Certainly there are power supplies (ie some Durst power supplies) that use a small current signal from the timer to turn the bulb on-off, without running the whole bulb current through the timer.

Which color head exactly is it? I'm sure that this can be sorted out.

The easiest solution would be to just get a timer that has another safelight socket. Timers are relatively cheap and sometimes free.

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It's a 45 Dichro Color head, the older model.

Yes, the head and color computer stay powered while the lamp is extinguished. Hence my suspicion that the "lamp plug" simply supplies signal to some kind of SCR or other arrangement that actually powers the bulb. But I don't have schematics, and I hesitate to tear into it if it's working properly. If it was broken I'd have it apart already.

I want to get a good F-stop timer, but I stumbled across a decent Paterson digital timer for the opening bid. (Shipping cost more than the timer!)

I've got small ice-cube relays in my junk box, and so long as signal and a small incandescent bulb for the safe light are all I have to power I can do it for the cost of my labor, which - although *I* think it's very valuable on the open market - seems to be more plentiful than spare money these days. If I need something capable of powering the 250W bulb, then I have to scrounge some more. I don't have anything quite that stout on hand.

Of course, I could simply start scrounging now, and note that a 250W is easily under 3amps for a contact rating. Places like All Electronics have stuff like that occasionally.

I don't really see a problem if the safelight is on while the enlarger is printing. Why worry about it?

I have an old unicolor digital timer that shuts off the safelight when you hit the focus switch, in order that you can see better to focus. When you hit the print button, the safelight stays on during printing. I have the safelight over my enlargers on the timer circuit, and the safelight over my wet area on a pull-chain.