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Old 30th May 2021, 09:18 PM
chrisb chrisb is offline
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Question Durst transformer

Hi all,
New to the forum and newish to darkroom printing. I have a krokus 44 which I got from my dad and has been fine for my 35mm printing but I want to start printing my 6x6 negatives. On an impulse I got a Durst m707 from eBay for 30 which was 5 minutes up the road. The problem is that the transformer was missing. Has anyone used a generic 12v 100w transformer to power a colour enlarger head? Or will I have to pay a lot for a proper Durst transformer?
Thanks
Chris
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Old 31st May 2021, 04:47 AM
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Uwe Pilz Uwe Pilz is offline
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You may use any transformer which give 12V and 100W. Such transformers are very popular for Halogen spots.
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Old 31st May 2021, 07:59 AM
John King John King is offline
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If you want to get a correct Durst transformer which will have the appropriate connectors try a company called Second Hand Darkroom who are one of the forum sponsors. Look on the top of this page there is a dark grey bar and the company is shown as the 2nd from the right. I have lost count of the times I have used them. His prices are definitely not over the top!

They are not open today so give them a call tomorrow
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Old 31st May 2021, 09:49 AM
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Welcome aboard.

By "transformer" I assume you mean a voltage regulated power supply? For colour printing it may be better to find a power supply that is intended for an enlarger as it seems that it is common for enlarger power supplies to output AC but the equivalent DC voltage from a standard regulated supply should be fine. I'm sure someone here must have done this in the past.
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Old 1st June 2021, 08:51 AM
chrisb chrisb is offline
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Thanks all for your responses. Another question regarding set-up, I currently use a sonoff basic R3 and the FADU timer app to control my krokus which works off the 240v, is there any issue with having the sonoff on the 240v side of the transformer? There's often a lag when you cut the power to a transformer but is this minimal because the power needed by the lamp?
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Old 1st June 2021, 06:37 PM
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Bob Bob is offline
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Quote:
Originally Posted by chrisb View Post
Thanks all for your responses. Another question regarding set-up, I currently use a sonoff basic R3 and the FADU timer app to control my krokus which works off the 240v, is there any issue with having the sonoff on the 240v side of the transformer? There's often a lag when you cut the power to a transformer but is this minimal because the power needed by the lamp?
That is the only way you can use a Sonoff R3 - it can only switch mains voltages as it gets its own power from the mains input and switches the live side using its relay.

There is a lag when switching the enlarger lamp off, but there is also a corresponding lag when you switch it on. In practice, these are unlikely to result in the same amount of light hitting the paper in each case so if you are making test strips using multiple exposures then you should make your final print using the same sequence of exposures (this is the same with most timers unless it has a sensor to monitor how much light has reached the paper during the exposure, or if the enlarger has a shutter). There is another potential issue with using a regulated power supply in that the circuitry can introduce other delays as capacitors charge and discharge etc.

For example, if you determine that your best test strip is the 4th strip along which adds up to a total of 16 seconds then you should not use a single 16s exposure for your final print - use the same 4 exposures as for the test strip. Saying that, depending on several variables, it may be close enough for practical purposes, you would need to try it and see. The FADU timer has an offset setting that lets you adjust the timing to allow for this disparity in on/off exposure, but it is a bit awkward to determine how many milliseconds to add or subtract as it is a trial-and-error process. The method is explained in the manual.

An alternative option is to use the SINGLE mode for test strips so each strip gets its own single exposure instead of a cumulative one, but that obviously takes longer.


Cheers, Bob.

P.S. If you are using the "PULSE R3" Lamp Controller mode with the AUTO strips method, try setting a 2 second Delay between strips as the Sonoff can be VERY slow to respond in this mode causing things to get out of sequence and messing with the timing. If your network is fast enough I would suggest using "BASIC R3" mode instead. Ideally, reprogam the Sonoff with the FADU firmware!

Last edited by Bob; 1st June 2021 at 07:08 PM.
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Old 2nd June 2021, 08:22 AM
chrisb chrisb is offline
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Thanks Bob that's a really useful reply. I hadn't thought about running through the same timing sequence as the test strip. I really like the FADU app, it's worked very well in my first few darkroom sessions with my krokus so I'm keen to keep using it when I set my Durst up
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Old 3rd June 2021, 07:01 AM
Martin Rick Martin Rick is offline
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I have to use 2x12V 50W transformers connected in parallel for the colour head of my Meopta. They don't have a regulated output so I have to live with minor fluctuations of output voltage.
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