On my krokus I use 500 W lamp, during the focusing a diode is connected on the line,  when
print is bypass.

very low cost solution.

1st: Minimize the voltage sag.  See if you can plug the enlarger
into an outlet that goes straight to the fuse box without any
major appliances on the same line.  You may need to string a heavy
duty extension cord to get to a low-demand AC outlet.

2nd: Add regulation.  The standard fix is a "Sola" ferroresonant
transformer.  These are made by many firms (including Sola) and
are sometimes called something slightly different, usually
variations on 'regulating', 'transformer' and 'resonant'.

Solas last forever.  Get a used one as new ones are expensive.
Look around at electronic surplus outlets on the web, ebay,
a WTB posting on the darkroom marketplace usenet group and
photo web sights with buy/sell forums.

Some dichoric and VC heads use 80V quartz-halogen lamps with a
special regulating power supply box. I am sure one
is available in a standard Omega 'D' fitting.

Other fixes have been proposed: certain UPS computer supplies, those
that constantly charge the batteries and constantly run the
computer from those batteries, will provide regulation -- these
are usually big ticket items, though.  Some of the smaller
UPS may also work well in this application.

There was a little box called a "Wein Regulite" that works if
the voltage sags but can't regulate if the voltage goes much
above 117 VAC.  The design and construction are dubious, use at
your own risk.  In fairness I have not heard of any catastrophic
failures with this device.

The choice of the regulation may vary depending of the voltage of your
enlarger's lamp.

Mine uses a 12V/75W and after having built an electronic one, I opted
finally for a commercial switching regulated supply:
http://www.bonavolta.ch/hobby/en/photo/v35suply.htm
Please note the comments regarding the supply protection types as some will
not work properly with lamps due to the high inrush current when switching
on.

Regards,

There have been a number of queries about voltage regulation. Are you
all so sure that is the problem? My guess is that voltage is unlikely
to be the issue.  I had the same thoughts about some erratic results
but found that my problems were a product of my processing methodology
which included a very dilute print developer. I assume there are other
examples of erratic processes that can cause the same frustration.
Check into it before buying another gadget.

Signed

No gadget(if possible) Nick

I use a TrippLite Voltage Regulator and Conditoner model LS604AX that will
handle up to 600 watts. It was originally used to isolate a large printer.
Works great.

It is small, about 4x5x6, kind of heavy, around 10 pounds. Perhaps one will
show up on eBay but I have not seen them.

Go to http://www.tripplite.com/products/conditioners/index.cfm. Mine looks
identical to the one on the left. Click on the LS606M or the LS604WM for
possible candidates. I don't see a price. I got mine when it was going to be
thrown away with an old printer.

Bert

There are several, at least 2, on auction at eBay. Here is one, found by
searching for "tripp lite":

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=32830&item=3089993047&rd=1

and

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=32830&item=3089998098&rd=1

or, for higher ratings

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=50968&item=3808409740&rd=1

Price seems reasonable for now but beware of shipping charges. The thing
weighs around 10 pounds, not including packing. This one is similar to the one
I mentioned earlier but mine has four outlets instead of the two this one shows.

Note that these are line conditioners and voltage regulators, they are not
UPSs, they have no batteries, just active regulation circuits. They are also
not just spike suppressors, they have active regulation and will protect
against brownouts and spikes.

Disclaimer: I have nothing to do with the sellers on the above mentioned auctions.

Bert