Heathkit part wanted

[Jack Gifford]

Looking for a power transformer for a Heathkit model 10-20 ignition 'scope, but will look at any 110v transformer that has a secondary winding in the neighborhood of 1,800 volts.

[JimL]

There must be something out there, but if you have to... you can make your own.  I used to make them as a kid.

Start with a piece of 3/4" steel rod, about 6" long.  Cover it with a layer of friction tape.  Put 100 winds of lacquered wire onto the rod, covered by another layer of friction tape.  Then wind 1600 winds onto the rod (outer windings), working back and forth for even distribution.  Cover with friction tape.  I used a hand crank to turn the rod, with the other end clamped into dad's lathe with the belt disconnected.

I used a low wattage 110V bulb as the load for the primary windings.  Your outer windings will be your 1800 volts A/C.  I made mine mounted on a piece of wood, with a hole partially drilled to accept the end of the steel bar.

Dont hook it up without that lightbulb for a primary winding load, or things turn into flame and smoke!  That method is more exciting if the garage is attached to the house, mom is in the kitchen, and you've left the door into the house open.

JimL

[Jack Gifford]

JimL- You might be worse than me, as far as finding the s..l..o..w..e..s..t.. solution to a problem! Nevertheless, thanks for the suggestion. At least a couple of times I've resorted to winding my own coils. But from the looks of this transformer it would require many times (10? 20?) more turns than your example, to get the inductance up into the required range.

It looks like I'll be buying a non-functional model 10-20 that I found on eBay- cheap and not too far away- and hope that it has a good power transformer.

[salt27]

Jack,
  What the heck are you up to?

  Don

[JimL]

Unless my memory is really wrong, it should be the turns ratio that does the job.  1600 divided by 100 is 16, multiplied by 110-115V is pretty close to 1800 volts, but the amps get really small.

Hmmmm....that does sound too long for us old guys.  It seemed so easy when I was 10 years old!

JimL

[salt27]

I can't wait to be 10.   

[Seldom Seen Slim]

I haven't looked recently - but'll go to some of my ham radio parts catalogs and see if there's something out there.  I assume it's for the high voltage for the CRT so there's not much current, right?  For the sake of immediacy -- go to www.aesham.com.  They're in Milwaukee and are one of the (few) ham radio shops still catering to us. 

Other than buying a new one - how 'bout going to something like American Science and Surplus (www.sciplus.com)?  They've got all sorts of stuff, from goofy to strangely interesting.  Sometimes they have extra-good stuff.  Once upon a time I saw and didn't buy, and I've kicked myself for not buying, that 1000' roll of bright yellow caution tape.  It was marked "MINES! CAUTION!  MINES!".  Wouldn't a string of that around your pit bring some interesting looks from visitors?

[Jack Gifford]

salt27- About a year ago I had bought a "junk" 10-20, got it working well, and enjoyed having it available since almost eveything I own has points/coil ignition. The transformer died a couple of weeks ago, so I'm just trying to get it going again.

jimL- Yes, the turns ratio needs to be about as you said. But to get the overall impedances (resistive plus inductive @ 60 HZ ) up to appropriate values (> 12K ohms at the primary, >170K ohms at secondary) requires a huge number of turns. These values would keep the power dissipation close to the 2 watts consumption of the original transformer and avoid re-engineering any circuit values (filters, tube bias dividers, etc.).

Slim- Thanks for the link to Science and Surplus- looks like my kind of place!

[manta22]

Maybe you can find a small neon sign transformer of the approximate voltage needed.

Regards, Neil  Tucson, AZ