Back in the late 70s the voltage regulated 19V power supply for my Minolta Mod III enlarger went bad. I converted it over to a 1/2 wave rectified non-regulated supply with a big diode. It has a 24V transformer, so half of that is around 13 measured volts.
I used the enlarger like that all these years. Now I letting my kids use that enlarger. The "Kodak Projection Print Scale" works great with kids, they can just pick out the pie that looks good. However, our printing times were not always under 60 seconds with Y/M multigrade filtration dialed in.
So, I decided to look into optimizing the light output.
The enlarger has used the EKG bulb all these years. That is the original type bulb and it is rated at 80W at 19 volts. Well, since I only have 13 volts, I thought a 12 or 13V lamp would get me back to optimum intensity.
A search of various bulbs led me to the DED bulb. It is 85W at 13.8V with the same GX5.3 2-PIN base. Cost about $5.00. It is on order, but I'll post my results when it arrives.