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Old 8th November 2004, 11:27 AM   #1
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Default 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. 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* 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.

Click the image to open in full size.
http://www.tridonicatco.com.au/Medie...304_au/HID.pdf
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Old 8th November 2004, 12:22 PM   #2
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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.
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Old 8th November 2004, 12:24 PM   #3
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Another view showing the winding which looks about 1mm size wire. Note the broken winding cover.

I haven't given this thing a name yet.
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Old 8th November 2004, 01:29 PM   #4
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So... Are you going to knock over more light poles in order to salvage their ballasts?

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Old 9th November 2004, 05:31 AM   #5
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Actually, no. My car is a "one-hit-wonder"...
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Old 9th November 2004, 05:53 AM   #6
Will is offline Will  Malaysia
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I'll bet tube heads will pose the big Q - "Will it sound good ???"
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Old 9th November 2004, 06:31 AM   #7
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Quote:
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.
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Old 9th November 2004, 06:01 PM   #8
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Yeah. Would be skookum in either a big chunky SS amp or an even chunkier tube amp (can you say 2 amperes plate current? ).

Tim
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Old 9th November 2004, 06:48 PM   #9
Fuling is offline Fuling  Sweden
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Interresting. Unfortunately I haven´t been able to figure out what those things are called in Swedish, so I can´t google for them...
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Old 10th November 2004, 10:10 AM   #10
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Default Just what the doctor ordered.

Quote:
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. Will be interesting to hear of somebody's results.
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