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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
why are old flybacks pancake shaped, while modern ones are cylinders? what about the winding arangements in the flybacks pancakes and cylinders? i make my own flybacks b ut i worry about parasitic and stray factors.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Perhaps it is because modern insulating techniques allow the entire coil to be a lot closer to the core, whereas older types get away with just moving the higher voltage further away? I really have no clue, just a guess!
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The 70's saw the demise of the valve eht rectifier,and damper. and the design of harmonic tuning of the dag and distributed capacity of the secondary windings. this required tighter coupling with the long coil rather than the PI type. In short, they are tuned to resonate at a harmonic of the drive pulses, (15734 Hz in NTSC) , while the primary windings act as an autotransformer to match the yoke at the fundamental. For the full story you have to back through 60 years of years of crap that was rendered obsolete by non-crt tvs.
The coilers are doing the same things it seems, with the exception of winding coils with series diodes *distributed* along the length of the secondary to end up with DC pulses. (integrated flybacks)
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ok radiotech, so the old flyback is called "PI", and there was no attempt to manipulate stray inductance or capacitence, by spacing them in narrow bands, with many layers, ending in the HV termial at the outer most circumference layer?
If i make my own flybacks in the way Uzzors and others describe, i would prefer the old PI technique,,is this wise? i do not use resonance or diodes in my designs.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The old flybacks drove a single vacuum tube in half wave recttification to crt anode with dag (outrside black graphite grounded spray acting as half a filter cap through the glass to inside metalization. They just wound enought turns in a corona manageable form to give the voltage. Sometimes a doorknob was used, occasionaly a tripler. the model worked well right up until transistorized or scr drives,and color TV demanded control of ringing.
The lower impedance of transistor current drives meant the wattage losses of the horizontal output stage were much less (mainly anode heating.) Early solid state drivers were not tollerent of ringing, so the tranny was restyled and harmonically tuned secondaries were patented and used, The last tubes to go in the change to solid state were the damper and horizontal output. ( which was nice for hams because the last made tubes were excellent and cheap for transmitters).
A good thing to do when salvaging flybacks is get the date code of the chassis to know what genre of parts you have.
As to what they were trying to do, they were trying to make coils that did not burn out due to insulation failure. The energy from the transformation in the flyback went three ways . a. Drive the core of the deflection yoke. b. light up the CRT c. Provide a B+ boost voltage recovered as damped out di/dt energy when the beam in was pulled back fast by reversal of the field of the yoke.This voltage fed back to increase power efficiency. In solid state sets the flyback also powers the rest of the set just like a smps. Shutdown control is mandated due to X-Ray regs so the whole set is held up by safety logic which enable the power on to remain satisfied. (an expensive nightmare to troubleshoot.) Benson D.G (1980's) and Fink DG (1950's) 'Television Engineering Handbook' good sources.
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about flybacks from 1950-1970....
