using triplers in old color sets

[DaveWM]

I was pondering the idea of rewinding a fly, where only the HV section failed.

Seems the issues would be working with the very fine gauge wire needed to get the number of turns up to the working voltage AND having to deal with insulation to prevent arc over between windings.

IF the lower voltage windings are ok (or even if not an you need to rewind the whole fly) why not just use thick better insulated wire and only step up to about 10kv then use a commercial tripler to get get the HV, no more 3a3 and have access to a focus supply as well.

I did try directly connecting a tripler to the plate of a horz out once on a working set and got 11-13kv (IIRC).

I know some of the older sets (pre CTC-12) have flys with a lot more taps for various purposes.

[miniman82]

Originally Posted by DaveWM

Seems the issues would be working with the very fine gauge wire needed to get the number of turns up to the working voltage AND having to deal with insulation to prevent arc over between windings.

These are the least of your worries- it's striking a balance between inductance, the resistance of the winding, and distributed capacitance. These influence the resonant frequency of the whole transformer, get it wrong and all your work will be for nothing. Never mind the fact that you need the special winding rig...

[DaveWM]

that is why I was thinking of just replacing the HV winding leaving the primary alone. At least all the inductance matching to the yoke and the aux drives hopefully would not be adversely effected.

[hi_volt]

The resonant frequency of the flyback transformer is highly dependent on the interwinding capacitance of the secondary. If you remove half of the secondary windings, your resonant frequency will increase and the transformer will no longer be properly tuned.

[DaveWM]

Originally Posted by hi_volt

The resonant frequency of the flyback transformer is highly dependent on the interwinding capacitance of the secondary. If you remove half of the secondary windings, your resonant frequency will increase and the transformer will no longer be properly tuned.

Is the resonant freq of the flyback independent of the resonant freq of the eff coil inductance? if not perhaps compensation for change in the fly could be offset by a change in the LC of the eff coil.

[old_coot88]

Here's an excellent treatise on the arcana of flybacks in general. It addresses the impracticality of trying to rewind them.
http://www.repairfaq.org/sam/flytest.htm#flydis

[wa2ise]

If you have a bad flyback from some other but similar set, where the HV winding is still good, in theory you could remove from the bad flyback the bad lower voltage windings until you have only the HV winding. I'd leave the cardboard layer just under the HV winding, to avoid destroying the fine wire turns (take care when you disconnect the bottom of the HV winding, with that fine wire). Now with the flyback with the bad HV winding, remove all of the HV winding. You'll have to disassemble the flyback, and keep careful track of the spacers used to make gaps in the ferrite core, as you need to put them back. If you get lucky, the good HV winding will fit over the other windings. But most likely it won't, but you could place the HV windings next to the other windings. Just be sure it mechanically fits, with plenty of clearance for the outer rim of the HV winding.

I never tried this, just thinking out loud.

About 35 years ago, just out of college I was working on SS video monitors, converting one to operate at 31KHz scan rate. But we needed to get the flyback time down, and we removed the HV winding. This cut the flyback time by about half. We needed it short, to avoid overscan of the video image. We used a separate HV power supply for the CRT.

[old_coot88]

Just brainstormin' a bit more on the tripler issue.. Never done it, but supposin' you could find a good flyback from a SS set that uses a tripler. Take the HV winding off from it, and graft it onto the subject fly in the manner described by Wa2ise above. Seems like that oughta keep the resonance of the 'hybrid' intact. Like i say, just musin.

[Chad Hauris]

Some of the later RCA 19" tube-type series string sets, and the Zenith 4-tube sets use triplers in their original design.

[old_tv_nut]

There are two resonances of interest in a flyback. The first is that of the primary and yoke with a discrete capacitor, which sets the retrace time. Reflectance of the secondary into this circuit probably affects it, but I can't say how much, because when I was designing flybacks we always went from an existing design, never tested a primary only by itself.

The second resonance of interest is the secondary. It is formed by the secondary inductance and distributed capacitance (not a discrete capacitor). While the total turns sets the output voltage, the number of layers/turns per layer plus the spacing between layers plus the characteristics of the potting compound determine the distributed capacitance. This second resonance is tuned by adjusting all these things that affect distributed capacitance. In the usual designs I worked on, the secondary was tuned to the third harmonic of the retrace. Some later ones were tuned to the fifth harmonic. The idea was to have the third harmonic in the secondary out of phase with the retrace pulse at the high voltage winding top, and have just the right amplitude so that the third harmonic tended to flatten the top of the transformed flyback pulse. This meant that the high voltage rectifier had a broader flatter voltage pulse input, making the high voltage output more stable with varying amounts of beam current. In other words, the impedance of the high voltage supply was reduced so that it was "stiffer" and there would be less variation with beam current, meaning less blooming. It is this improvement that you will lose if you wind a new secondary without redoing it by trial and error to get the tuning right.

[Steve McVoy]

I have successfully used a tripler to replace the HV winding of a flyback in our Hoffman 19 inch color set. I know of others in England who have done the same with color sets:

http://www.earlytelevision.org/hoffm...storation.html

[timmy]

Originally Posted by old_tv_nut

There are two resonances of interest in a flyback. The first is that of the primary and yoke with a discrete capacitor, which sets the retrace time. Reflectance of the secondary into this circuit probably affects it, but I can't say how much, because when I was designing flybacks we always went from an existing design, never tested a primary only by itself.

The second resonance of interest is the secondary. It is formed by the secondary inductance and distributed capacitance (not a discrete capacitor). While the total turns sets the output voltage, the number of layers/turns per layer plus the spacing between layers plus the characteristics of the potting compound determine the distributed capacitance. This second resonance is tuned by adjusting all these things that affect distributed capacitance. In the usual designs I worked on, the secondary was tuned to the third harmonic of the retrace. Some later ones were tuned to the fifth harmonic. The idea was to have the third harmonic in the secondary out of phase with the retrace pulse at the high voltage winding top, and have just the right amplitude so that the third harmonic tended to flatten the top of the transformed flyback pulse. This meant that the high voltage rectifier had a broader flatter voltage pulse input, making the high voltage output more stable with varying amounts of beam current. In other words, the impedance of the high voltage supply was reduced so that it was "stiffer" and there would be less variation with beam current, meaning less blooming. It is this improvement that you will lose if you wind a new secondary without redoing it by trial and error to get the tuning right.

just an out there question about the hv donut of a flyback. when the hv part, donut, is wound it starts off with a single wire that is like hair which i understand but so then its wound into what they are to produce the hv needed so that wire in the beginning where does this wire attach to because the other end is the wire for the hv rectifier. in wanting to switch donuts because its bad in doing this how is one to know where this wire goes. would it go to ground or some other place on the lower voltage coil. i have asked this befor but no one seems to know where the beginning of this donut wire starts out. there has to be a beginning and end of this hv coil in order to produce the hv and the end being the rectifier cap.

[DaveWM]

if its an autoformer its all one long winding.

[timmy]

well i was talking about a fly such as one for a ctc12. i thought that a coil would need one end to ground or some other connection to complete the induction process.

[old_coot88]

Originally Posted by old_tv_nut

...In the usual designs I worked on, the secondary was tuned to the third harmonic of the retrace. Some later ones were tuned to the fifth harmonic. The idea was to have the third harmonic in the secondary out of phase with the retrace pulse at the high voltage winding top, and have just the right amplitude so that the third harmonic tended to flatten the top of the transformed flyback pulse. This meant that the high voltage rectifier had a broader flatter voltage pulse input, making the high voltage output more stable with varying amounts of beam current. In other words, the impedance of the high voltage supply was reduced so that it was "stiffer" and there would be less variation with beam current, meaning less blooming. It is this improvement that you will lose if you wind a new secondary without redoing it by trial and error to get the tuning right.

Interesting about the impedance-lowering effect. Just learnt something new.
I always assumed the HV 'tire' was sharply resonant somewhere around 70-80 khz (or kilocycles as we called it in those days). Would that be somewhat correct?