View Full Version : Flyback Questions


Alan Sailer
06-09-2017, 11:07 AM
I am hoping to get some general information about flyback transformers.

First question. When a flyback for a color TV is designed to supply 25kV to the CRT after rectification,
does this mean that the flyback is putting out 50kV peak to peak AC?

Second question. What is the rough amount of power that a color TV flyback will handle? I'm assuming
it is related to the size of the core but some approximate number would be interesting.

Finally, is there a list (catalog?) somewhere that gives the output voltages for the
line of Thordarson FLY-*** transformers?

Thanks so much for any replies...

Cheers.

miniman82
06-09-2017, 11:48 AM
No list for specs that I'm aware of, just the catalog showing what number flyback and the application.

Voltage: not really sure, it's not AC though it's a sawtooth wave form. I would expect peak to be slightly higher than what you get at the anode wire though, since you will get some drop through the rectifier tube (most will tell you how much on the data sheet). For example, around 30 or 40v loss is typical with the 3A3 rectifier. Not that it makes a big difference to the flyback or picture tube when you have 25,000 on tap.

Power: I can't speak for all sets, but the color roundies I have seem to use power and shunt tubes around the 30w class (6CB5 output and 6BK4 shunt tube). Doesn't mean that's the power the flyback sees, I would expect a little less on average like maybe 25w to avoid exceeding tube ratings. But there again we aren't talking about a low frequency AC mains transformer here, it's a ferrite core high frequency transformer operating in class C.

Electronic M
06-09-2017, 12:14 PM
I am hoping to get some general information about flyback transformers.

First question. When a flyback for a color TV is designed to supply 25kV to the CRT after rectification,
does this mean that the flyback is putting out 50kV peak to peak AC?

Second question. What is the rough amount of power that a color TV flyback will handle? I'm assuming
it is related to the size of the core but some approximate number would be interesting.

Finally, is there a list (catalog?) somewhere that gives the output voltages for the
line of Thordarson FLY-*** transformers?

Thanks so much for any replies...

Cheers.

Out of curiosity; what are you trying to build?

Alan Sailer
06-09-2017, 12:37 PM
Miniman,

Thanks for the information. I am using them in my application near resonance which is in the 20-30kHz range.

If there is a list somewhere that shows which Thordarson flybacks are used in which TVs that would be potentially
useful information. I might be able to find which TV has has a certain flyback inside.

For example I have a FLY-352 transformer that turns out to be a replacement part for a CTC-22 and runs at 25kV DC.

Electronic M,

I am building my own plasma globes and I need a few power supplies that can get to about 25-30kV peak to peak.

https://www.flickr.com/photos/8763834@N02/33438980170/in/dateposted/

Don't worry that I will be using up too many flybacks. I only need a few good units. The world seems to have
mostly lost the ability to make good high voltage AC coils so I have to find suitable vintage coils.

Cheers.

old_coot88
06-09-2017, 01:57 PM
Don't forget that the HV winding is not tuned to the 15,750 scan rate or even the first harmonic of it. It's tuned to the retrace or "fly-back" spike which is in the RF region. Actual resonance would be probably around 75 - 80 Khz. (Maybe someone can give a more exact figure.)

Electronic M
06-09-2017, 02:02 PM
Miniman,

Thanks for the information. I am using them in my application near resonance which is in the 20-30kHz range.

If there is a list somewhere that shows which Thordarson flybacks are used in which TVs that would be potentially
useful information. I might be able to find which TV has has a certain flyback inside.

For example I have a FLY-352 transformer that turns out to be a replacement part for a CTC-22 and runs at 25kV DC.

Electronic M,

I am building my own plasma globes and I need a few power supplies that can get to about 25-30kV peak to peak.

https://www.flickr.com/photos/8763834@N02/33438980170/in/dateposted/

Don't worry that I will be using up too many flybacks. I only need a few good units. The world seems to have
mostly lost the ability to make good high voltage AC coils so I have to find suitable vintage coils.

Cheers.

That sounds like a cool project, however I think your wasting money trying to do it with tube based flybacks/circuitry.

Solid state flybacks are VERY easy to drive into the 25-40KV region. Back in college I was broke and scrapped a lot of curbside 80's - 07 CRT sets. I became fascinated by plasma speakers and decided to build one...It was very easy to do so with a flyback from a free junk modern CRT set. All I needed was a 555 chip for the oscillator/audio modulation driving a power FET, connected to 10-20 turns of wire wrapped around the core of a fly from an Solid State set*, and a 20V power brick for the whole shebang. I had that thing maxing out my HV meter at 40KV and producing crystal clear audio....I even modded the spark gap into a Jacob's ladder for a while (it sounded terrible as a plasma speaker that way, but looked cool) and had ~3-5" arks at the top of the gap. :D

* I think I can find the web page with the schematic if your interested.

The average tube color TV fly alone is worth $50 or more...For that money you can build several HV supplies with solid state flybacks and parts. You'd be better off selling the tube fly to a collector and building a SS supply.

Whatever you decide to do I'd love to see the end result/circuit design.

Alan Sailer
06-09-2017, 02:19 PM
Tom C,

That approach would certainly make my life easier. Unfortunately all modern flybacks have several built in rectifiers
and put out a signal that will not effectively drive my plasma tubes/globes. When I first started this project I did
exactly what you proposed and it wasn't good enough.

There is a small community of plasma artists (I'm no artist) that are currently suffering from a lack of good HV AC
transformers. I'm glad that I only need a few.

The video I posted shows some globes powered with a few HV coils that I bought from Ebay. They were not complete
flybacks just the secondary coil. I have them in oil for cooling and to help prevent breakdown.

Unfortunately I have no idea what voltage they are intended to support. For all I know I am grossly over-stressing
them and they might die in a few months.

Which is why I am trying to find a few flybacks of known performance to make some (hopefully) well designed and
reasonably spec'ed power supplies.

Cheers.

Electronic M
06-09-2017, 04:12 PM
You may want to look at some of the early Solid state transformers....Those used an external recitfier box. Those boxes usually contained a doubler, tripler, or quadrupler circuit. If you find one for a doubler or tripler you may be able to get enough HV from one of those...They usually over built those flys such that they could run near 2-4X their ratings and live*.
Another possibility would be to forcibly short the internal diodes on newer flys. It may be possible to do it internally by taking one apart, or you could hit it with more than the designed voltage for a while. IIRC lightning will cause power supply diodes to short in the main PS stages of TVs. So maybe a brief jolt of ~100KV will short the internal HV rectifiers in a modern flyback.

Have you considered a tesla coil? IIRC those are AC output and easy to make out of easily obtained materials.

* For example early solid state Zenith sets had problems with capacitors failing in the drive circuits and causing the HV to shoot up to ~60-100KV The voltage would arc through the CRT glass and cause the glass to crack and the CRT to fail.

etype2
06-09-2017, 04:23 PM
Alan,

I can't offer much advise except to say your project is very cool. Watched the video. About 40 years ago, I bought one of those plasma globes that responds to human touch or sound. They were sold at Spencer's Gifts, Sharper Image and the like. Still have it today and it works.

etype2
06-09-2017, 04:27 PM
Electronic M,

I'm very intrigued by your descriptions of the plasma speaker. In theory a perfect sound source with zapping visual effects. How cool is that. :-)

Electronic M
06-09-2017, 04:47 PM
Electronic M,

I'm very intrigued by your descriptions of the plasma speaker. In theory a perfect sound source with zapping visual effects. How cool is that. :-)

Oh, it was very cool. I brought that thing to my college when I built it, and several of my peers and professors were rather wowed by it. There are some very interesting youtube videos of plasma speakers in action. Mine had very little bass response (typical/expected), and some issues with the arc producing white noise that I never had time to sort out, but it was the most linear tweeter I can recall hearing. Electronic music like Threashold from Steve Miller Band's Book of Dreams album had an almost unreal crispness, clarity and accuracy compared to listening to such tracks on cone or horn tweeters.

Life kinda buried me in work (then distracted me) when I built mine as a proof of concept, but I do plan to eventually get back on refining some into a practical system.

Alan Sailer
06-09-2017, 04:54 PM
Electronic M.

In my limited experience with HV diodes they always fail open. This is based on several diode deaths that I facilitated.
Even if you could get the diodes to fail short I doubt it would help. One of the reasons the original design went to internal
rectifiers was to keep from dealing with AC HV issues. Insulation requirement for AC are much more stringent than DC
because AC will propagate through insulation due to parasitic capacitance.

In my AC HV (~20kV) circuit I can run my finger across an insulated wire (40kV DC rated) and get a blue corona discharge
on my fingertip. This doesn't happen with DC.

And corona kills insulation over time.

As far as Tesla coils, I have built a few to try out. And bought a few more. let's say about seven so far. They can be
pretty impressive if the coil is CW and lower frequency. Low frequency means big for an air coil.

Unfortunately they make a poor choice for lighting plasma. Noisy and hazardous. A hit from a tesla coil may not
hurt you. But it sure isn't pleasant.

Cheers.

wa2ise
06-09-2017, 05:06 PM
First question. When a flyback for a color TV is designed to supply 25kV to the CRT after rectification,
does this mean that the flyback is putting out 50kV peak to peak AC?



The waveform looks much like a square wave at about 7% duty cycle. The positive peaks go up to 25KV, the lower side peaks at around 4KV.

Alan Sailer
06-09-2017, 05:14 PM
wa2ise,

That's very interesting. That would fit with my kindergarden levl understanding of flyback mode ie the input drive creates a magnetic
field in the core. When the input drive stops, the field collapses creating a voltage spike in the output coil.

Thanks much.

zeno
06-09-2017, 05:29 PM
Using rough numbers, foggy memory & I am NOT an engineer.........

Typical set horz tube draws 200ma at 400V so power is 80 watts.
IIRC a pair is used in home brew ham amps to give a solid 100W.
Waveform at horz out plate is DC with 1KV spikes on top of that
going +. ( DO NOT MEASURE !)
Spikes are very narrow at 15,750. Horz tube is running
very deep class C. The tube is biased off ( -60 to -90 on G-1 )
most of time.
You may want to get an RCA, GE or Sylvania tube manual to help.
Also as many of the same FBT's as you need so you only
engineer them once.

73 Zeno:smoke:
LFOD !

miniman82
06-09-2017, 05:30 PM
Don't those globes usually have a cascade multiplier running at line frequency? I don't see why you'd need a flyback from a color set per se, you should be able to get away with one from a B&W set then put a doubler one it.

benman94
06-09-2017, 06:16 PM
You're looking at minuscule current here. Call up Arlynn at Heyboer, ask him to wind you a mains transformer 117 VAC to 5 kV at a milliamp or so, and then use a Cockcroft-Walton arrangement to get up to whatever HV you need. Not terribly elegant, but it works, and has for 85 years...

Alan Sailer
06-09-2017, 08:16 PM
zeno,

Your rough number seem in the ballpark to me. I'd be surprised if someone told me horizontal output transformers
are driven at 10 watts or a thousand watts.

Don't worry about measurement stuff I'm perfectly happy with HV as long as it's low power. I've been messing with
HV AC and DC for a number of years and have remained shock free.

miniman82,

All the globe power supplies I have seen (about seven so far) have been some sort of oscillator driving MOSFET(s)
which directly drive a HV step up transformer, usually an un-gapped flyback style. Cascade multiplier put out DC,
not useful for this stuff.

benmann94,

I'll check out Heyboer. I'm guessing they do coils?

The same comment on the Cockcraft-Walton, DC is no good for driving a capacitively coupled plasma globe.

Cheers.

Findm-Keepm
06-09-2017, 11:30 PM
Miniman,



Don't worry that I will be using up too many flybacks. I only need a few good units. The world seems to have
mostly lost the ability to make good high voltage AC coils so I have to find suitable vintage coils.

Cheers.

And with the dearth of good flybacks for pre-1967 sets, you may find it hard to find one cheap. A good Fly 276, 277 or 308 is hard to find.

I'm like others in my recommendation - for a few microamps of current, look at cheap Black and White flybacks from the tube era, perhaps something for a 19 or 21" set, sure to be rated at enough current for a plasma globe. Without the capacitance of the CRT, they do put out a bit more of HV...we made a stationary 2" arc at a friends house one evening (drive was from an HR Diemen flyback tester ((EDIT: like this one: http://www.ebay.com/itm/HR-STVDST-01-Flyback-Transformer-Tester-/132206654484?hash=item1ec8217414:g:AgEAAOSw2xRYlU~ H ))) and the flyback was from a 19" Sanyo tube B/W set. The fly ate itself, presumably because we didn't load it like the yoke and CRT would normally. Arced to the core, and smoked the paper at the core.