Beware of Used 45S Beseler Color Heads

[Neil Poulsen]

I purchased a used 45 S Beseler Color Head and checked it out. Yes, each color worked just fine.

Later on, I noticed that there was a delay between when power was supplied and when the light came on. This delay could be either a split second or 10 or 12 seconds long. Bummer!

Yesterday, I checked out a second 45 S Beseler head, and it had the same problem, though not so pronounced. Again, Bummer!

I've heard of others with the same problem.

You get the idea; be careful about buying these heads used.

Mine's still usable. I plan to swap out the power for the light bulb with a connection to a $60 Variac variable, 600 watt (or so) voltage transformer. That way I can use the same 83 volt bulbs that are intended for the 45 S head. I will also connect the Variac to a voltage stabilizer.

 

[ymc226]

I have 3 Beseler 23 Dual Dichro S heads and one of them does the exact same thing except the delay can be a split second or 1-2 seconds. Your experience worries me that the problem might get worse.

Any electricians out there who can guess as to why this is happening and suggest a cure?

 

[nickandre]

I use one who's ones digit doesn't appear most of the time. How can I restore that?

 

[Nicholas Lindan]

You don't need a variac - just put a rectifier in series with the lamp as 1/2 wave rectified 120 VRMS is 83 VRMS. Beseler does just this when they put 83V lamps in an unregulated head.

 

[Photo Engineer]

I read somewhere several years ago that there is a simple fix for the problem. Beseler used to fix this if you returned the head to them, but I believe that they published the "fix".

PE

 

[ic-racer]

Related thread on converting the power of an Omega Super Chromega head: (there was a url link here which no longer exists)

 

[Neil Poulsen]

Great Idea!

You don't need a variac - just put a rectifier in series with the lamp as 1/2 wave rectified 120 VRMS is 83 VRMS. Beseler does just this when they put 83V lamps in an unregulated head.

Slick! Thanks for this idea.

I'll give it a try. I like this, because it removes a huge variable, which is the Variac. I was thinking that I might also need to get a voltage meter, so that I could reset the Variac if ever it got changed.

 

[Neil Poulsen]

I read somewhere several years ago that there is a simple fix for the problem. Beseler used to fix this if you returned the head to them, but I believe that they published the "fix".

PE

I wonder if it involved circumventing the internal voltage regulator. I'll bet that would be fairly easy, if one had a circuit diagram as a guide.

I called both repair places listed on the Beseler site. Both said that they couldn't get parts and had stopped repairing 45 S heads. Interestingly, B&H still have new ones up for sale at full price.

 

[ymc226]

I just found this. It appears the solution requires a part which may be hard to obtain and the necessity to solder parts onto a board. Not an easy fix.

(there was a url link here which no longer exists)

 

[Photo Engineer]

Yes, that is the reference. Thanks for finding it. Opto-isolators are or were sold by Radio Shack. You might also try JDR Microdevices.

PE

 

[Denis R]

digikey

digikey has optoisolator approx 2k results

 

[Nicholas Lindan]

If the problem with the head is the Vactrol, and if it is an old head it quite well may be as they do burn-out, then...

The Vactrol used in the old heads had an incandescent bulb and a CdS element. The bulb was driven with the same regulated waveform (at a reduced voltage) as the enlarger bulb -serving as an analog for the lamp in the enlarger. By regulating the brightness of the Vactrol bulb the circuit regulated the light in the enlarger. Naturally the incandescent bulb burns out with time.

The modern Vactrol replacements use an LED for the light source. These can't be substituted for the original vactrol as: the LED requires a current drive while the lightbulb was driven with a voltage; the brightness/current relationship for an LED is different from the characteristics of a light bulb; the original used a CdS cell, modern vactrols use either a photodiode or phototransistor though EGG may still make them with CdS cells; the dynamic response of a lightbulb is very different from an LED, when fed a chopped waveform a lightbulb will still produce a relatively constant output while an LED will produced a chopped output.

Beseler at some point changed the design so it could use a modern Vactrol. You may be able to effect the same modifications to your head so it can also use a modern part.

The original light-bulb Vactrols are in great demand for restoring old electric guitar amps where they were used for the limiting circuit. The new LED Vactrols don't have the same attack/delay times as the originals and the amplifier doesn't sound the same.

Why someone doesn't go into business making old-style Vactrols, I don't quite know. All there is to them is a lightbulb, a bit of plastic tubing and a CDS cell.

 

[clayne]

The original light-bulb Vactrols are in great demand for restoring old electric guitar amps where they were used for the limiting circuit. The new LED Vactrols don't have the same attack/delay times as the originals and the amplifier doesn't sound the same.

Why someone doesn't go into business making old-style Vactrols, I don't quite know. All there is to them is a lightbulb, a bit of plastic tubing and a CDS cell.

Even though I don't have this head or even a Beseler enlarger, this info is fascinating Nicholas. I'm always interested in pro audio gear and music equipment - especially the classic analog stuff. Is the issue that the LEDs have too fast a delay or is it that they are now entirely "square-wave" in their response? I would figure a lightbulb would produce a typical knee'd response in it's output and hence result in more musicality for something like a limiting circuit.

Actually, is what we are describing basically the typical design of an electro-optical compressor?

 

[ic-racer]

The original light-bulb Vactrols are in great demand for restoring old electric guitar amps where they were used for the limiting circuit.

There is one in the tremolo circuit on old Fender amps.

 

[Nicholas Lindan]

There is one in the tremolo circuit on old Fender amps.

They are voltage controlled attenuators - so if the lightbulb goes to the output of an oscillator and the CdS cell changes the amplifier volume - presto: tremelo...

 

[Neil Poulsen]

This has been an interesting thread. I checked with Beseler right away. They no longer supply any parts. I spoke with the two independent repair services that Beseler lists on their site, and for lack of parts, they no longer repair the 45S heads.

I picked up the rectifier that Nicholas mentioned for 45 cents. I also picked up a capacitor recommended by the retail store that will connect between the output end of the rectifier and ground. This should help filter the signal a little. I could feed a regulated 120 voltage into this small circuit, but I doubt I will. I like the rectifier solution, because I can use the bulbs originally intended for the enlarger. At about $13 each from B&H, I'll get extras. As to installing the rectifier, I'll put it in series with the lamp as Nicholas suggested. The output side of the rectifier should lead to the light. The 100 micropico capacitor will connect this output side to the ground.

I have the Zone VI Compensating timer, and I've installed an extra sensor into the Beseler head. So, this will regulate the head. Note that I installed the sensor such that it's exposed to the light source, not the filtered light. There's a neat little mirror inside the head that reflects light onto the front dials that also works to direct light to the sensor. (When properly placed.) In this way, I avoid heat issues with the sensor, and it attenuates the bright light so as not to overwhelm the sensor. It appears to work great.

To anticipate a question, why install the rectifier, if I have the sensor. To answer, I don't like 12 second delays in my printing! In theory, it doesn't matter. But even with the sensor, it makes sense to have the head as consistent as possible.

As to all the fancy circuitry remaining in the head, it can run the fan.

 

[Nicholas Lindan]

Do you know the part # of the rectifier you purchased?

What is the size and voltage rating of the capacitor? 100 "micropico" isn't right (a micropico would by one millionth of one trillionth, or 100 atofarads).

 

[Neil Poulsen]

100 Microferads! (Thanks.)

 

[Nicholas Lindan]

I should update this -- do NOT put a filter capacitor across the lightbulb: it will convert the 1/2 cycle AC at 83 VRMS to DC at ~160 volts (which is 160V RMS, as for DC the peak, average and RMS voltages are all the same). 160V RMS will make for a very short lamp life.

The rectifier used should be rated at better than 600 volts and 5 amps. A rectifier diode similar to the 6A6, 6A8 or 6A10 would be appropriate:
http://www.diodes.com/datasheets/ds28009.pdf
There are many styles of rectifiers available that would work, one is certainly not limited to the above device.

 

[Steve Smith]

You don't need a variac - just put a rectifier in series with the lamp as 1/2 wave rectified 120 VRMS is 83 VRMS. Beseler does just this when they put 83V lamps in an unregulated head.

I assume my LPL 6700 also has half wave rectification as it too uses an 83v bulb but runs on 120v (from a transformer as I am in the UK with a 230v supply).

I always thought 83v was a funny rating for a bulb..... and I suppose I still do!


Steve.

 

[Steve Smith]

They are voltage controlled attenuators - so if the lightbulb goes to the output of an oscillator and the CdS cell changes the amplifier volume - presto: tremelo...

Perhaps on some lesser amplifiers! The good ones use modulated grid bias to create the tremolo.


Steve.

 

[rx7speed]

You don't need a variac - just put a rectifier in series with the lamp as 1/2 wave rectified 120 VRMS is 83 VRMS. Beseler does just this when they put 83V lamps in an unregulated head.

it should be less then that I believe. 120v peak to peak voltage would have an RMS value of .6xx (been far too long to remember). in a half wave recifier you would have about half of that value not counting any losses or inefficiency in the rectifier itself. also being half wave rectified ripple I would assume could be a problem.

but as I've said been away from electronics quite some time so I've forgotten many things and I was never huge into it to begin with. just enough to get myself some analoge amplifiers and distortion pedals setup.

 

[Andrew Moxom]

Does this apply to the Beseler 45 Universal heads? This is the head with 3 82volt bulbs in it. One for each color!! I have a used one of these that has been fine for 18 months. My older 45 computer dichroic head with a single bulb used to have issues with voltage regulators, but nothing like a delay. I cannibalized other used heads to get it working again.

 

[Nicholas Lindan]

Another common issue with these heads, or any head that uses halogen lamps, is the lamp holder. They get corroded and munged up with age and need to be replaced. They are often the cause of random problems. Lamp holders are standard parts.

 

[Neil Poulsen]

It Works!

It appears to work just great! No delay, of course. The only question I have is my wiring. But, I was careful in tracing the wires and using the proper gauge. I bought a 6A8 rectifier just to make sure. I was able to use the original cord that powers the lamp, and thereby was able to wire my circuitry through the safety switch. So, nothing works if the lid is up.

Must remember to turn on the fan, though. After rewiring, it's possible to turn on the lamp without the fan.

My thanks to Nicholas and all for their contributions to this thread. The neat thing about this slick solution is that, I can still use the Beseler recommended light bulbs. Will order some extra.

I should update this -- do NOT put a filter capacitor across the lightbulb: it will convert the 1/2 cycle AC at 83 VRMS to DC at ~160 volts (which is 160V RMS, as for DC the peak, average and RMS voltages are all the same). 160V RMS will make for a very short lamp life.

The rectifier used should be rated at better than 600 volts and 5 amps. A rectifier diode similar to the 6A6, 6A8 or 6A10 would be appropriate:
http://www.diodes.com/datasheets/ds28009.pdf
There are many styles of rectifiers available that would work, one is certainly not limited to the above device.