I bought this ancient desk lamp off eBay, and it was very bright.  ( 15 watt  desk lamp). When preheating manually the ends glowed VERY brightly and got purple flashing.  After 30 minutes the metal base became way too hot to touch. So I took the bottom off and it had a potted metal ballast.  It took a lot of work to get old ballast out and the new potted one in.  Now the base just gets warm! The old ballast is a Presto Elec Co made in Union City, NJ.  Lamp looks 40s.  I don't remember what bulb came with it. 

I had once found an old 15w size fixture...almost looked homemade. The lamp was EOL so I put in another lamp. It became quickly obvious it was being overdriven so I looked at choke ballast...turns out it was rated 30 watts. The lamp in there was 15w size but actually rated 30w! From what I recall of the lamp and ballast, (this was over 20 yrs. ago) it was 50's vintage at least.

Interesting Powell. What make/model is the old ballast?

Interesting Don, sounds like it might have been a prototype for an HO lamp which never made it to market!

Presto Electric Company out of Union City, NJ.   Lamp base now just stays warm. Before I could have grilled on the base.

During my "vacation" in Vietnam in 69-71 we had a double bulb 15 watt clamp on Dazer lamp that worked ok until one day the diesel generator that was powering our company compound went down below 120 volts and below 60 Cycles for about two hours before it was shut off.
 
It fried a lot of stuff like electric fans and radios.
It also fried the ballasts in the Dazer.

So the Dazer was broken and there was no FSN replacement available for the ballasts.
You could get the 15 watt bulbs through local procurement, but not the ballasts.
You could order a new Dazer clamp on lamp through procurement, if you wanted to wait a year or more.

So there it was broken and was going to be tossed out.
So looking at it, I thought why not make a ballast for it?

So I found two big bolts in the motor pool out of a Duce and a half and wrapped a lot of 24 gauge copper wire around each of them and hooked them up to the Dazer.
I just guessed on the amount of wire and bolt size.

Plugged it in and hit the start button.
It worked just like new.
The "bolt ballasts" were just warm but never hot.

They just looked odd laying on the floor with the wires going to the Dazer, but hey at least it worked.
The Dazer was still working fine when I left Vietnam.  


  

Wow Larry, that's quite the story, and keen thinking on your part! 
I'm trying to visualize how you made the makeshift ballast... Sounds like an interesting project...!

Wow Larry, that's quite the story, and keen thinking on your part!  
I'm trying to visualize how you made the makeshift ballast... Sounds like an interesting project...!

Yeah the bolt ballast worked on just a guess about the size of bolt to use and the amount of wire.
If I remember right it was a big bolt and a lot of 24 ga wire.
Really it was just a choke to limit the current to the bulbs.

I figured if the bulbs were too bright, use more wire.
If they were dim, use less wire.
But hit it right the first time.
I would guess not very efficient, but it did work.

And sure not UL approved.

Made two of them, one for each bulb.

When you are in a place like that, you have to improvise a lot.

Oh yeah, I got you now. The two bolts threw me off, but I get it now since it's one for each lamp. That's actually really keen. What you assembled was basically a bona-fide magnetic ballast, so it very well could have been efficient as one. I'm going to try that sometime. I think I'll need to get a reel of wire, though, since what wire I have isn't likely to be fine or long enough.