Awesome ! may I use it to ? 
Don’t forget to make a better heatsink.
IXYS seems to be the benchmark in linear MOSFETs
Thanks. This guy’s test is pretty extreme!
I have a home made ~55V e-load which I built about 30 years ago. The photo and the real thing are sort of rough. A true work of art, huh? 
I brazed the square steel tube frame together with an oxy-propane torch.
It has 200 mA, 2A, and 20A ranges. Each range uses an MTP3055E MOSFET driving 2 or 4 (I think TIP41) bipolars in a FETlington arrangement. So the FET is only a modest (not intended for linear use) device but it is only driving the power BJT bases so the current is not very high.
The heatsinks are only a couple of 0.1 or 0.125 inch (??) thick aluminum plates (no real fins). The thermal insulators are polyimide with a waxy thermal compound coating…I forget the tradename but that tradename may be long gone. Anyway…this is your Kapton speaking. 
UPDATE: I remembered the trade name of the insulators. They are Crayotherm. I really do not remember that they seem to be from a Czech company:
What does work REALLY WELL is to press the TO220 plastic bodies + rubber pad against the polyimide + heatsink (don’t use the TO-220 hole) with a square rod and machine screws.
In all that time with occasional use, nothing has ever broken and the fan (controlled by a thermistor) has never turned on.
Looking at the photo of the load, I’d guess, if it overheats, the plastic ties will melt, the metal heatsinks? the ties support will drop, and the power will disconnect? 
In that event, I will use it in Australia so that it will be mounted upside down and gravity will hold it together.
I am not sure that I could ever fix this thing if it breaks. Obviously I did not have KiCad when I built it. It is completely hand wired and I am not sure if I have my schematic diagram anywhere… 
In the lower right corner of the photo you see part of my 60 year old Belden “strip-it” wire stripper which looks like an overgrown staple remover. It really is good but it can pinch your hand badly if you do not watch it. Those are absoletely obsolute.
I’d thought this design was Bob’s rather ingenious idea for a 20 amp circuit breaker rather than a problem. It would save wear and tear on the fan. 
You may, this time only . . . and please, don’t wear it out. 
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Thanks.
I am very new to KiCad and struggling on two fronts and with getting my head around HOW to create what was required with new items. Searching on how to create symbols (google) gave me a headache as it pointed me to using Python … eeee another language to learn (only just mastering Java scripts into functions in Node-Red). I could not find how to create what’s required (end-end) in the KiCad Help (help was not in the downloaded version and the online help didn’t seem to match the version of KiCad I have installed).
Looks like I will do this retrospectively after I have mocked up the initial board design for testing. I have laid out the board (although for audio) using RF layout symmetry using my old tool (Visio) and created the photomask. Will etch, drill and construct the prototype for testing next week. Once I am happy with the slew resp I will then look at noise, distortion and power (then test protection as these devices are a little intolerant of short circuits [bad load]) but they are nice and linear. Although they colour coded the fets in parameter groupings to enable paralleling them without needing source resistors I am still using them. (plan on reducing from .2 ohm in steps of testing).
I am clueless WRT Python, but I create symbols easily and almost routinely. Maybe you encountered some AI hallucination? 
I have no observation supporting the idea that the symbol for a lateral FET is any different from other MOSFETs. The Exicon DS which I looked at had no symbol on it.
But anyway…the way to make a symbol is to copy and edit one from the standard symbol library. No need to create it from scratch. I have also never used a symbol wizard.
If you want to create a new symbol, understand that the new symbol needs to be in your own custom library. Start with something from the standard library or I will be happy to give you what I have. Give it a try. If you get stuck, this is the place to ask for help.
There is a version dropdown at the top right at the documentation website, needed now that the current version has been switched to 9.0. Here’s the section on creating symbols for 8.0:
But as said before, most people do not create symbols for simple devices, there is usually a generic symbol that will suit. There’s is certainly a P-MOSFET symbol you can use.
I posted this comment way up in this thread:
You will find the Q_NMOS_GSD and the Q_PMOS_GSD in the Kicad Symbol library named “Device”. Note, the order of the letters also denotes the pin numbers, so G=1, S=2 & D=3.
You will also find the various (depending on how you wish to mount the transistors) TO247 footprints in the Kicad Footprint Library named “Package_TO_SOT_THT”
“Device” actually. Although some people might want a library called “Discreet”. Back in the day we used to joke that ICs stood for Indiscrete Circuits.
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Nope. It’s called “Device”.
This is where you’ll find all generic symbols. Best place to look before searching for specific parts.
Thanks folks, brain fade. I was in the middle of discreetly correcting that indescretion and adding the “secret” way of relating the pin names with the pin numbers while you guys were posting.
I was an engineering intern in North Carolina about 55 years ago. A local colleague quipped:
“Are you working on one of them thar dee-vices?”
Calling it a “device” sounds a bit sinister… (film of early atom bomb tests).
This is not like you. Better check the definition of that spelling
TS Eliot knew all about cats and their discreet names. 
He certainly did know about their discreet/unobtrusive names. He also discussed their individual/discrete names.
I was always intrigued by his use of the spelling. Both would suit.