What could i possibly do with these huge transformers?

[Berni]

Connect the secondary as the primary, build an interesting 3 phase  cockcroft-walton ladder.  Of course the voltages would be well past lethal.  Think of the Jacobs ladder exhibit or all the things you could ionize (including yourself)

I wouldn't recommend doing that in the UK. Would be fine in the USA tho.

The magnetic field strength in transformers is designed to be pretty close to the saturation of the magnet laminate steel core when run at rated voltage. This allows them to get away with less turns on the coils causing the transformer to have less resistive losses, be lighter and cheaper to make. This also means that if you try to run a lower voltage winding at a significantly higher voltage it causes the core run into saturation, this causes the inductance of the wingdings falls off a cliff, this causes the input current to sharply rise and trips the breakers.

Good transformers for producing high voltage at high power are american pole pigs. They have a 110/220V secondary where you can feed your mains into and get a few kV out the high voltage side. They are not too common in 3 phase forms but you can wire 3 of them together into any 3 phase configuration.

These pole pig transformers are much more difficult to find in Europe because here its more common to have one large distribution transformer turning 20 to 100 kV down to 230V. Unforcenetly these transformers weigh a few tones and have rated powers in the range of 100kVA to 50 MVA. The magnetizing current on one of these likely exceeds the capability of a typical 3 phase residential service (About 16 to 30A per phase), so even if you could somehow get one you wouldn't be able to turn it on without blowing fuses.

[coppercone2]

I tried to open a module, but it is potted the hard way. It has a 1kW power dissipation, and I managed to break a module in that amplifier by running max. output current into a short. For sure, that module broke down due to too high junction temperature, but it took a while, so I don't think of internal thermal runaway but rather general overheating due to insufficient thermal sinking. The datasheet specifies some kind of SOA that covers the whole power dissipation at any combination of voltage / current as far as I remember. These old style modules are too old for the "many transistors" approach, I believe it's rather a single  transistor die inside.

Regarding your amp: 600kHz BW from 150V rails is impressive, too

Its also possible that it handles linear operation better just due to being a BJT. Its the modern MOSFETS with low Rdson and IGBTs that are the most famous for developing hotspots in the die and blowing up under extended periods of linear operation.

And yes getting this much bandwidth from it has involved a lot of hair pulling. My first attempt was a BJT output stage design, but at the required currents they simply would not switch fast enough. Many many hours in LT Spice later resulted in a redesign of the whole thing and the use of a MOSFET output stage. It used low gate charge high voltage FETs and a strong gate drive circuitry to make sure it switches fast enough. All in all it ended up being made out of about 30 transistors. The gain stages, current sources, bias generation and gate drive was done with BJT transistors as they are fast enough at low currents. A few more transistors are used to switch the amplifier between standby and active within a few microseconds(Standby reduces power use to near nothing and also floats the output to eliminate the need for a Transmitt/Recieve switch later on)

The damn thing loved to oscillate in weird ways with all of that bandwidth. With certain loads at certain output power it would become a 400 MHz oscillator with significant output power even. I would never believe that a big power MOSFET can output a signal this fast. This particular oscillation turned out to be a LC circuit formed by the internal structure and tough hole pins of the MOSFET itself. Adding damping capacitors and ferrites in the right places calmed things down as well as putting ferrite rings on pins of MOSFETs. More LT Spice, cursing, some electrical shocks and exploded components later and eventually the thing was stable with all sorts of loads(Even heavily capacitive or heavily inductive and surviving dead shorts) and worked perfectly.

The resulting powerful output of the amplifier once ended up driving a pocketwatch sized lump of piezoelectric element so hard it exploded from the mechanical stresses.

does anyone else get anxiety imagining themselves having to deal with this?

[capt bullshot]

The resulting powerful output of the amplifier once ended up driving a pocketwatch sized lump of piezoelectric element so hard it exploded from the mechanical stresses.

does anyone else get anxiety imagining themselves having to deal with this?

No, why should I?

Anyway, regarding pole pigs and European distribution transformers, one can acquire "Messwandler" (Potential Transformers) here (e.g. 10kV : 100V), these can make nice jacobs ladders too: http://wunderkis.de/britzel/index.html

Or simply MOTs (microwave oven transformers), remember ElectroBoom nearly killing himself with one?

[T3sl4co1l]

A friend has a potential transformer that's very modestly rated... the trick is, because they're intended to sense the potential very accurately, the coupling factor is very high.  They're not intended for many VAs, but a high VA capacity is necessary and sufficient for their desired operation.  Indeed, they have much lower leakage than a conventional type does, which makes them... very exciting indeed, for high voltage testing!

In practical terms, it really just means you need a ballast on the primary side, and then you can use them for whatever you like.

Needless to say, the friend has documented just how large of an arc you can get from a residential (US) feed, before the breaker opens the circuit.

Tim

[Berni]

does anyone else get anxiety imagining themselves having to deal with this?

Oh don't worry it was not as violent as if the thing was full of gunpowder or something. It just made a bang and flew apart into chunks. I think most of the bang was due to the silver electrode plating vaporizing due drawing an arc.

Most electronics that operate at above hundreds of watts are capable of making some spectacular failure modes that involve bangs, sparks or fire. Also 100V to 200V is a range where voltage is high enough to give you a decent shock, but still low enough that you are not terrified of getting close while running. For something operating at kilovolts at 100s of watts i would certainly not come close until i can see the plug is pulled and caps discharged as a shock there can quickly become deadly.

Anyway, regarding pole pigs and European distribution transformers, one can acquire "Messwandler" (Potential Transformers) here (e.g. 10kV : 100V), these can make nice jacobs ladders too: http://wunderkis.de/britzel/index.html

Or simply MOTs (microwave oven transformers), remember ElectroBoom nearly killing himself with one?

Ah i didn't know about these measurement transformers. I could imagine something like that can output a good deal of power and transformers can usually be massively overloaded in terms of current for short periods as it takes time for all of that copper to warm up.

Yeah MOTs are by far the easiest way to get into the 2kV range. I wouldn't be surprised if someone here of there manages to kill themselves while messing with one, we just don't hear about a lot of the cases.