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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Nice project Xray!
On a related note, if you buy "Motorola" TO3 transistors from a Chinese or Hong Kong EBay seller, they are probably fakes! Not to say that they won't work in your project, they just have nothing to do with Motorola or On Semi and you are "feeding their economy" more than you think.
My favourite high power TO3 transistors are the MJ15024 and MJ15025, available from all major outlets like Mouser, MCM, Digikey and so on.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
U4R1A wrote ...
Did you use a normal audio transformer from radio shack or something special?
No, not from Radio Shack. It's a "tube type" audio output transformer that I found on Ebay. It has a rather high turns ratio, so a small signal on the low ohms winding produces a fairly high voltage on the high ohms winding. When used as an audio output transformer, the high impedance winding becomes the primary winding, and is connected to the plate of the audio output tube. The low impedance winding becomes the secondary, and drives an 8 ohm speaker. The way I'm using it in this circuit, the 8 ohm winding is the primary, driven by the speaker output of a radio or amplifier, and the secondary drives the modulator transistors. This particular transformer has a fairly wide audio bandwidth, and so it works very well for a plasma speaker application.
Registered Member #3505
Joined: Sun Dec 12 2010, 06:03AM
Location: Albuquerque NM
Posts: 108
I've been shopping around for a "tube type" audio output transformer. I was wondering if you could post some specs of yours so I could narrow my search a little.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
U4R1A wrote ...
I've been shopping around for a "tube type" audio output transformer. I was wondering if you could post some specs of yours so I could narrow my search a little.
The one I used is still available on Ebay. It's item number: 110793396931 "TF103-48 5W CHAMP OUTPUT TRANSFORMER 4/8OHM MADE IN USA"
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
I though I would share what happened to my flyback transformer last night when I ran it via a half bridge. 7 primary coil turns drawing just under 3 amps on 36v. For some reason adding or removing just 1 turn makes a big difference in arc length. I had it running on 8 turns before this and the arcs were smaller and current draw was just over 1 amp @ 36v input!
The arc ignition gap wasn't even very big yet the insulation still failed!
Worth noting that the audio modulation was much louder when the flyback was covered in corona.
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My Plasma Speaker
