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Old 05-26-2012, 08:14 AM
Slider2732 Slider2732 is offline
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Join Date: Mar 2011
Location: Muskogee, Oklahoma, USA
Posts: 1,006
I'm about 3 miles from our RS, but it's not worth bothering with. They don't even have lead-free solder, let alone the transformers everyone is using for lighting at the moment. Pretty much all of it is big TV's, cellphones and boxed computers. Oh, there are the odd co-ax connectors, but really somewhere like Walmart is just as good for parts in the automotive section !

Speaking of parts...glad to hear about the CRT chassis. You'll find excellent 1500V transistors bolted to the flyback aluminium. Some have TIP series transistors in them, nearly all will have IRF630 and equiv MOSFETS.
I built a copy of the SEC 18 of Dr. Stiffler's purely from CRT chassis parts, runs from an AA

As far as resistance on the Base..and i'm no EE, so is just an understanding. The Positive supply goes directly to one end of the L1, the other end of it connects to the Collector. So powering of the Primary is based on the always connected Positive supply and the firings of the transistor to the other end of it.
The resistor stops the full supply voltage hitting the transistor Base, or it would never switch. It would be constantly seeing nothing but the overpowering full supply voltage, anything that the L2 may do would be swamped. To do anything, the transistor needs to switch rapidly, turn on the Collector, then receive the pulse back from the L2 into the Base to continue again.
With a resistor of 1meg, most emphasis is being placed on the feedback from the L2. A 1K will work fine, but more draw will be seen on the circuit, through the transistor. In other words, wasted as heat for the switching function we are using it for and more so with more voltage. Add high hFE (amplified current) and the transistor can heat up very quickly.
The 1Meg translates as a power limiter, but enables enough Positive to initially kick start the transistor into that feedback condition of L1 and L2 interaction.
Often, the resistor can be pulled once oscillations start, the L2 is now active and the Positive supply is no longer needed into the Base. The current the transistor then uses is dictated by the L1/L2 interaction and loading of them
Where a circuit only runs at certain set resistances (like never with a 1meg resistor) then a tuning LED becomes really handy. It's just the standard Emitter to Base connection, with the Positive leg of the LED connected to the Emitter (conventionally would be wrong way around). The feedback will run down the LED to ground and allows careful tuning of the L1. The brighter the LED, the better set up the circuit is. Once set up and the LED bright, you should be able to throw in a 1Meg resistor and it start up fine, while using less input energy to do so and resulting in a cooler transistor.
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