Voltage regulation

[squinonescolon]

Does anyone have a recommendation for a voltage regulator? I usually never do more than a couple of prints at a time but this weekend I did 40 to give away as small presents and they were all over the place. There was a difference by as much as 1/3 of a stop in some of the prints. Now, it could be that the my Besseler digital timer if off somehow, but I've noticed my safelight getting slightly brighter or darker on a couple of occasions, so I think that might be the culprit (The house is over 100 years old) I used divided Ansco 130 specifically because I wanted consistency, so I'm stumped as to what it could be.
I have an Aristo Cold Light Head DL1200 with the warming circuitry.
I use divided Ansco 130 at around 70 Degrees
I was using Arista EDU Ultra VC RC Pearl 5x7
Any ideas?
Steven

 

[Nicholas Lindan]

Try testing.

Late at night, when the voltage from the power company is steady, make two prints: one with all the appliances in the house turned on; one with the appliances turned off. If the prints are the same then something else is wrong, if they are different then look for a Sola CVS regulating transformer on ebay. A 1/3 of a stop should also show up on a light meter so you may get by without making prints and just use the light meter.

Cold light heads are a bugger when it comes to consistency, even with the heater. You have to make prints at evenly timed intervals, with a few dummy intervals at the beginning to get things stabilized. A voltage stabilizer won't help here.

 

[jp80874]

It is quite possible that a voltage regulator is what you need. On the other hand the problem may be in the cold light. I use an Aristo 1212 cold light for 8x10 on a converted Durst 138S. See pictures in my gallery. I would suggest you read about sponsor RH Design’s StopClock Vario. It has a light probe or sensor and software which helps maintain consistent exposures. http://www.rhdesigns.co.uk/darkroom/html/stopclock_vario.html
I have had mine for 3-4 years and am very happy with the results.

John Powers

 

[Denis R]

buy OLD

I bought a General Electric Voltage Stabilizer
rated for
60 cycles
.250 Kva
95 to 130 Line Volts
115 Volts out

cat. 67 g 752
outline K 5808590 BR
patent 1859115

FY Made in USA

has 4 transformers and 2 caps
weight about 50 lbs

 

[DWThomas]

Been a long time since I had entanglements with them, but there are "constant voltage transformers" using some sort of ferro-resonant magic, made by Sola and Topaz, sometimes sold for use with computers. They are a bit brutal price-wise, but might occasionally be found through some of the electrical surplus houses. You need to check on the capacity too, the smallest might not be enough to handle the load of your enlarger. A quick look showed some through Newark and Allied stores, but they are asking 4x what I paid for my enlarger!

 

[Mike Wilde]

As Dave noted, CV transformers, with a ferroresonant coil will ride out blips and even voltage outputs to a near constant.

The downside is that they are hummy things. I have mine connected downstream of the timer, which may introduce turn on transients, but the hum drove me nuts. I go into the darkroom for almost a kind of mediation compatred to my day job.

Mine was found used at a camera store about 5 years ago for $60, and I snapped it up, knowing it was a a bargan.

If I was to do it from the start, I would mount it at the main panel, and then run a circuit dedicated to the enlarger timer from it.

 

[Nicholas Lindan]

"constant voltage transformers" using some sort of ferro-resonant magic ... Newark and Allied stores, but they are asking 4x what I paid for my enlarger!

Surplus they go for pennies on the dollar with a decent unit selling for $20 - $100. They are heavy, so expect shipping charges to be high.

There is no point in getting one any bigger than you need.

The other solution, as John stated, is a compensating timer. Along with RH, you can find units made by Metrolux and Zone IV (VI - ?). You can also use a graphic arts 'light integrator' made by nuArc, Olec, Douthit & others - often found for $50 or so if you are lucky. A compensating timer will mitigate the variation due to both line voltage sags and warm up.

 

[squinonescolon]

The timer it's probably the best way to encompass all possible problems. I sure wish you made the gizmo Nicholas. I would much prefer to buy from this side of the pond. And I love the meter I got from you.
Steven

 

[Nicholas Lindan]

I love the [Darkroom Automation] meter I got from you.

If you have the meter then monitoring for light changes is pretty easy.

If you are making a series of one negative then zero the meter on a spot on the image and before every print just check that the meter still reads zero (plus/minus a smidgen). If it is off a whole lot then adjust the timer to compensate.

I have been thinking of a compensating version of the f-stop timer, but I am temperamentally unsuited for cold light heads.

There is also a problem of using a meter with a compensating timer as both the meter reading (and hence the exposure set into the timer) and the timer itself will both compensate for illumination dips and you end up with overcompensation. The RH website warns of this problem...

 

[squinonescolon]

Lateral thinking, I love it. Thanks.
Steven

 

[ic-racer]

A coldlight with just the warming device will be repeatable only if allowed to cool to the baseline temp between exposures. The warmer is a good, simple, cheap and reliable device, but it has its limitations.

Do you still have the original head for your enlarger?

 

[ic-racer]

What I would do if I were still using my cold light head, is to get one of these stick-on theremometer strips and put it on my cold light head. Then, I would use my graph that I posted above and do a time-temp compensation for each exposure.

In your case, use any meter to make your own compensation graph.