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Circlotron 8th November 2004 11:27 AM

Chokes 4 everyone!
You can buy transformers just about anywhere which is a good thing when it comes to diy. It is a different story when it comes to =chokes= though. Your average electronics parts shop will rarely have what you are looking for. :rolleyes: This is not good because with chokes you can do things that are either not possible any other way, or are possible but with a great loss in electrical efficiency. Class A amplifiers are a good example.

Anyway, I was driving down the road the other day and there was this light pole that had been knocked down by some car. It was the type that has two 250W mercury vapour lamps. I stopped and went over for a look. The actual light part of the whole thing was smashed beyond any hope of repair, and in particular both the *ballasts* :angel: which in this case weighs about 3kg had pulled free of their mounting and broken various things inside the fitting.

Seeing the whole thing was so badly damaged I rescued the two ballasts from going in the rubbish and took them home. There I measure one and it was about 230mH and 1.72 ohms resistance. What's more, it has a gapped core so it will support DC so it could be used as a power supply filter or a source / drain load in a class A amp!

Even if you don't have a broken street light nearby, these ballasts are very readily available at any electrical wholesaler anywhere in the world basically! They come in all kinds of sizes and are basically the same kind of thing as a fluorescent lamp ballast but much bigger. I did see an 1800W one somewhere.

Circlotron 8th November 2004 12:22 PM

2 Attachment(s)
Anyway, this is a pic of one of the actual units I got. It has class H insulation so it can tolerate very high temperatures. The rated AC current is 3A but I think you could go a bit higher if ambient temperature is only moderate.

Circlotron 8th November 2004 12:24 PM

2 Attachment(s)
Another view showing the winding which looks about 1mm size wire. Note the broken winding cover. :smash:

I haven't given this thing a name yet. :dodgy:

stappvargen 8th November 2004 01:29 PM

So... Are you going to knock over more light poles in order to salvage their ballasts?


Circlotron 9th November 2004 05:31 AM

Actually, no. My car is a "one-hit-wonder"... :smash:

Will 9th November 2004 05:53 AM

I'll bet tube heads will pose the big Q - "Will it sound good ???"

Geek 9th November 2004 06:31 AM


Originally posted by Will
I'll bet tube heads will pose the big Q - "Will it sound good ???"
Of course we will! ;)

We usually dabble in inductances of 5H to 20H though.

Sch3mat1c 9th November 2004 06:01 PM

Yeah. Would be skookum in either a big chunky SS amp or an even chunkier tube amp (can you say 2 amperes plate current? :D ).


Fuling 9th November 2004 06:48 PM

Interresting. Unfortunately I havenīt been able to figure out what those things are called in Swedish, so I canīt google for them... :(

Circlotron 10th November 2004 10:10 AM

Just what the doctor ordered.

Originally posted by Geek
We usually dabble in inductances of 5H to 20H though.
Today I measured a 36 watt and an 8 watt fluorescent tube ballast. (240v 50Hz type) The 36 watt one was 39.5 ohms DC and 212.3mA @ 100VAC = 1.49H. The 8 watt one was 178 ohms DC and 67.3mA @ 100VAC = 4.7H. Being gapped, these will handle DC just fine. :cool: Will be interesting to hear of somebody's results.

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