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Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
I went to a local electronics supply place yesterday and stumbled upon this flyback transformer. Judging by looks it seems pretty old. Its a Triad D-219 and after probing the secondary with an Ohmeter, I have concluded that it is an AC flyback. It came in a nice little box with some stuff that looks like tissue paper and had a little sheet diagramming the secondary pins and which taps where connected where. I assume I just connect to the secondary across whichever two taps are the furthest away from each other for the most voltage but correct me if I'm wrong. Here are pictures of the transformer and a scan of the document that came with it. The first of my questions is where would I find a schematic for a driver. I want to drive it using the actual flyback topology (sawtooth wave, switch off as fast as possible). If someone could come up with a way of driving it with like a triode or something that would be in keeping with the vintage look of the transformer, that would be awesome, otherwise I am not to picky. The other question I have is can anyone figure out what the primary inductance is? It is just one turn around the core. Also would it be wise to immerse this in some type of transformer oil to protect it? I just don't want to damage it and being as its not completely potted with epoxy fill it seems kindof vulnerable to the secondary breaking down especially since I don't know the voltage it is intended to be driven at.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The single turn you have mistaken for the primary is in fact the filament supply winding for an EHT thermionic diode rectifier. Note that high voltage insulated wire has been used for the winding, as the filament is directly heated, and therefore at EHT voltage.
Now as for the rest, you are one lucky guy, cos what you have here is an Oudin coil, a special case of high voltage autotransformer, only rarely seen.
The coil tap marked "5" with a flying lead is the tap for the LOPT valve anode - this is the tap that drives the whole device in normal televsion use.
The thick red wire coming out of the winding is the high voltage output.
The other taps are likely to be for the picture tube scan coils and a booster diode.
Very strictly speaking, this type of device is not a transformer, but a special case of a choke called a disruptive discharge device.
This is a relatively low power device, perhaps from a small domestic portable television.
Thermionic valves are high impedance devices when compared with transistors, so you will not be able to use the original "primary" tap (5) to drive it.
I would suggest you remove the single turn filament winding, and use the freed up space to wind a new primary which is electrically separate from the main windings. You can then take your high voltage between terminal 1 in the diagram, and the other end of the winding connected to the fat red wire with the valve top cap on it.
My guess is that this LOPT ("flyback") was used in a small portable black and white television, so the output winding may have produced as little as 5kV.
If you want it to last, don't over-drive it, or try to draw long arcs from it, else it will fail quickly. The high-voltage over-wind was probably designed to produce only 100 - 200 uA, (compared with 1-2mA for a large colour TV LOPT) and will over-heat if you try to draw too much current from it. And should you over-drive it with too high a voltage, it will flash over internally and fail.
Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
If the winding I have mistaken for the primary is a filament winding for a valve, does that mean I could drive this thing with something like an 811A triode?
Proud Mary wrote ...
The single turn you have mistaken for the primary is in fact the filament supply winding for an EHT thermionic diode rectifier. Note that high voltage insulated wire has been used for the winding, as the filament is directly heated, and therefore at EHT voltage.
Now as for the rest, you are one lucky guy, cos what you have here is an Oudin coil, a special case of high voltage autotransformer, only rarely seen.
The coil tap marked "5" with a flying lead is the tap for the LOPT valve anode - this is the tap that drives the whole device in normal televsion use.
The thick red wire coming out of the winding is the high voltage output.
The other taps are likely to be for the picture tube scan coils and a booster diode.
Very strictly speaking, this type of device is not a transformer, but a special case of a choke called a disruptive discharge device.
This is a relatively low power device, perhaps from a small domestic portable television.
Thermionic valves are high impedance devices when compared with transistors, so you will not be able to use the original "primary" tap (5) to drive it.
I would suggest you remove the single turn filament winding, and use the freed up space to wind a new primary which is electrically separate from the main windings. You can then take your high voltage between terminal 1 in the diagram, and the other end of the winding connected to the fat red wire with the valve top cap on it.
My guess is that this LOPT ("flyback") was used in a small portable black and white television, so the output winding may have produced as little as 5kV.
If you want it to last, don't over-drive it, or try to draw long arcs from it, else it will fail quickly. The high-voltage over-wind was probably designed to produce only 100 - 200 uA, (compared with 1-2mA for a large colour TV LOPT) and will over-heat if you try to draw too much current from it. And should you over-drive it with too high a voltage, it will flash over internally and fail.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
"Very strictly speaking, this type of device is not a transformer, but a special case of a choke called a disruptive discharge device.
I wish I had that phrase when I replaced those sticky beasts back in the day: I could have charged an extra few dollars and not gotten a bit of argument !
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
UbuntuNinja wrote ...
If the winding I have mistaken for the primary is a filament winding for a valve, does that mean I could drive this thing with something like an 811A triode?
Not a chance! The single turn filament winding on your LOPT would have been used to heat a miniature EHT rectifier, such as EY51, which required 6.3V at 80mA. Other EHT rectifiers of this wire-ended type could get by with just a few volts and even lower current.
811A is a very different sort of animal, and while it still needs only the 6.3V (a very common standard for valve filaments and heaters) it guzzles 4A - FIFTY times more current than the little EY51.
Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
I got it for like $7.50. It was not some special they were having on old parts. Just found it in the transformer section and bought it. I also got a broken variac that I need to make a wiper for and then it will work. I got that for $10. I thought it was a pretty good deal considering new variacs can be more than $100!
radiotech wrote ...
RCA, tv, 1956 that could use a flyback like that and the wiring used. edit the 6DQ6A was known for snivets!
How much did it cost and was it in a lot of old specials they were selling; Just think of its value to a vintage television restorer !
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Good find with the Variac.
This is what was used to test flybacks and deflection yokes back when your flyback was used:
Note there is two setpoints--one for air core flybacks and one for the metalic composition types. Somewhere on the Forum is a picture of an air core flyback so if you see one in that store you will know what is is.
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Flyback Transformer Info
The single turn filament winding on your LOPT would have been used to heat a miniature EHT rectifier, such as EY51, which required 6.3V at 80mA. Other EHT rectifiers of this wire-ended type could get by with just a few volts and even lower current.
