Finn Hammer, fusor update.

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Maciek Szymanski
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Re: Finn Hammer, fusor update.

Post by Maciek Szymanski »

And one note regarding the corrugated tube. Generally the conductance between the high vacuum pump and the chamber is the key factor for the pumping speed. In fact, if the conductance is smaller than the pump throughput the pimping speed will be limited to the conductance value independent of the pump size (a "hole to ideal vacuum" case). The pump throat diameters are usually matched to the pump throughput. For other hand the fusor chamber pumped by passage matched to the pump throat will be evacuated very efficiently but the deuterium will be consumed and pumped out with the same efficiency...
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Joe Gayo
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Re: Finn Hammer, fusor update.

Post by Joe Gayo »

For turbos, there can be a large difference in pumping speed between heavy (N2, O2, CO2, etc) and light gases (He, H). This can be used to great advantage to conserve D2 but reduce background pressure.
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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

For the most part, ideal conductance on smallish chambers can rip a chamber down to the basement real fast, in a well sealed system. Likewise, as noted, you then wind up strangling off the wonderful vacuum conductance so often expensive to achieve once D2 is introduced to literally destroy the beautiful vacuum you have created with ideal matched and maximized conductance. The result, in the end, is at least a fabulously pure vacuum into which D2 is introduced. The silly result is that you must ruin the chamber vacuum by filling the reactor with flowing D2 at a pressure equal to what might be expected of a well used mechanical pump!

I have always been amused by this sad fact in fusor operation. The concept of a sealed vessel fusor, properly pressurized, will work for but a moment in time. I learned this in 1999. Such a sealed device will fuse well, but will bury the D2 in the walls in a few minutes decreasing pressure steadily in a well sealed spherical device. This phenomenon is at the very heart of the early X-ray tubes with no filament, operating at high pressures. Ultimately, these early tubes went "hard" and the power supply could not produce the amount of x-rays needed. (Current through the tube at any voltage determines the x-ray flux) Technicians were kept busy in big hospitals delicately regassing those early tubes with side arms meant to accomplish this task. The modern high vacuum "Coolidge tube" put them all out of work, for the most part.

If one is not hung up on the best conductance in molecular flow regime and has the time to pump to an acceptable level using a less than ideal conductance, the purity of D2 during operation will be acceptable and pinching off the D2 flow will have a much broader adjustment range. Also, the D2 purity will increase steadily as you load the walls to boost fusion.

This is not a suggestion for deliberately limiting conductance, but more of a reasoned methodology specific to what we know as "the fusor operational experience". In the end, do as you wish as it all works in the hands of any experienced operator of their specific fusor. Learn as you gain experience in operation.

The Farnsworth system of the mid-sixties in their best mark II prime with hot filament pigatron ion guns often had reports of 1-2 microns of D2 with 140kv applied at a few ma. This produced great numbers mostly due to the focused ion guns. All of the original team members that I interviewed noted that it took a couple of hours fiddling to balance and set up the "guns" to achieve those results. In some cases, during these tedious adjustment sessions, as the voltage was raised, burn-throughs, melted screens, arc-overs, and other issues ended the session that never came to be as shut down, disassembly, and repairs were made. (1-2 day downtimes)

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Maciek, Joe, Richard,

Thank you for taking the time to do calculation for me, and writing it up in a way that I can understand.

With regard to the corrugated tube, it probably does not matter a whole lot in fusor operation, although it is always nice to hit low pressures quick. And the purity of H2 is determined by the low pressure to start with.
The Turbo can run in standby mode, around 60% or 54KRpm, but even this is probably too fast for comfort, I wish I had a controller with full speed controll, but that will be for another time. I hope to get away with an almost fully closed gate valve, turbo on standby (because without the dual vane pump, I cannot work against the 2 torr of foreline pressure) feed 1ccm of H2 and see.

But frankly, from now I had better stop fantasising, and wait untill I have got hands on experience. You guys all know howto, I have yet to try it.

I have had a good day in the workshop, where great sacrifices were made to the god of swarf:

IMG_20210424_192441.jpg

I finally got the bulkhead clamp for the viewport manufactured, in copper and phenolic, to stay in line with the steampunk theme. The copper ring holds the 6mm lead glass which I schrounged from a Lesker wiewport. The paper phenolic clamps a KFviewport glass against the o-ring.

IMG_20210424_210215.jpg


I know that during the first learning experience, I will be looking at the plasma directly, but by restricting myself to the 30kV supply, and by having lead glass between plasma and myself, I can be safe.


Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

In the spirit of documenting the build as it progresses stepwise, here are a few additions to the build:

I got the grid manufactured, 1.6mm tig rod and copper.

IMG_20210506_163250.jpg

Nested nicely inside the chamber,

IMG_20210506_164936.jpg

Another thing that was mentioned was to get rid of the ugly corrugated tube from turbo to main control valve: It did help on the pump down time.
.

IMG_20210521_084406.jpg

Then I got the flow controller mounted, and the piping routed:


IMG_20210522_111710.jpg
This was interesting, because I could now start to get an impression of the range of pressure control I will have, and it fits the bill nicely.
with the turbo on full speed and the main controll valve fully open i get from 3 - 15 micron with 1ccm to 5ccm
with the control valve almost shut, I get from 11 to 42 microns with the same flow figures.
I am feeling a lot more confident about the ability to controll pressure with this addition under the belt.


This is the rig at present, notice that the electricals are temporary, shielded controll cable is waiting to be fitted.

IMG_20210522_111800.jpg

The trained eye will notice that I finally received the calibrated Baratron, and it is a marvel to behold, even though it has the penaltry of a 4 hour warmup time.

I think that I have talked about field controll before, this is something I feel strongly about, since I have decided to run this system dry, without any oil to insulate, or cool for that matter.

The feedthrough looks like this:

IMG_20210523_124718.jpg

Look at all the ugly protrusions just begging to present themselves to the first rogue partial discharge, and create a grounded arc. Uff, ugly!

IMG_20210523_124814.jpg

That was more like it, but only half of the story, 1/3, really :-)
field.jpg

Here is the finished article. Perhaps overkill, I don't know, because the feedthrough may well puncture through the porcelain (I think it is allumina, really) but it is a cool addition and if all fails, I can still use it in another episode.

That's all for now, it is the power supply that is being put into a nice box, that awaits attention now, and a couple of Ludlums in the mail too.

Cheers, Finn Hammer
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Mark Rowley
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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

It’s a work of art Finn!
Did you custom spin the lower flange toroid?

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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Mark,

Thanks for your kind words.

The 3 toroids are turned out from solid bar, spinning is something I am looking into, but for this one-off it was simpler to just turn them out of bar stock.

Cheers, Finn Hammer
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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Wow! You have really documented far better than any others have do on their first pass. The system is plus ultra looking and you have exchanged a lot of money for "the right stuff". I like the field control, but Bar stock!!! You are a better man than I Gunga Din.

Fortunately, we have one of the original Tesla coilers from the first years of the 1989 Teslathon attending regularly to date. He perfected the art of spinning and always shows up at every Teslathon and HEAS October event with toroids for sale at the flea market. Last Year, due to covid, he did not attend, thus, breaking his perfect run over the 32 years of attendance. All of my lab's toroids were spun by John Freau. I think the largest he ever spun was a 10" and the smaller ones like 6 to 4 inch are the ones he normally brings now. He did note that he isn't doing it so much now and only spins a couple for sale at the HEAS flea market. He once sold them by the dozens. We are all getting old now and the tedium of such work for limited rewards is weighed much more seriously as we all have a limited time remaining.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Sorry, double post, see below
Last edited by Finn Hammer on Mon May 24, 2021 3:38 am, edited 1 time in total.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Richard,
I have 2 of John Freau's 6 x 1 1/2 inch toroids, and a single 13 inch. Great stuff. John was a regular and very valued contributor to the Pupman list.
I also have tooling for 600mm x 170mm toroids and a good relationship with the spinners shop, so can deliver....
I even had tooling made for reentrant Van de Graaff 400mm top electrodes made. Still some in stock of those too, but the tooling got lost, unfortunately.

It takes 2 pieces of tooling to spin a toroid shell, one for the concave portion, and one for the rest, so if I was going to spin these toroids, I would be looking into even more turning from bar. The tooling can be made from tufnol, or other phenolic types of thermosetting material, but the stench from machining these materials keeps me from doing that, for the most part.
I had planned to make the grid from EDM graphite, but one hole drilled, and a single pass on the bar, on the lathe, convinced me that turning graphite is for another day, when I get a proper point dust extractor setup. Just don't want to foul up the shop with carbon dust.

Cheers, Finn Hammer
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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Great work Finn. I am glad you already have some of John's fine work. I wish you could meet him in person. He is a calm, very retiring and reticent person who is incredibly easy to like. Perhaps if you ever make what few HEAS October events are left in me, you can meet John.

Your effort is one that mimes my own in its temporal journey, which I find the best way to get into fusion. (Slow and easy - Read, do, absorb, correct the do, read some more, do some more, repeat) Of course, you have the best of us to soak up a lot of hard won knowledge. This can shorten the journey, but still, you move at the right pace, taking advantage every wrong thing made right over the years here. It is the right way to do it.

I wish others would enter this way.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

I had first light the other day.

At this point, I knew that the solutions I would come up with would probably have to be altered along the way, possibly in short order, so I allowed myself to delve into the fine art of jerry rigging, the ballast resistor being the first item to receive my left hand attention:

first ballast.jpg

You may be able to see the 3x16 matrix of VR68 resistors, they did not last long......


Next attempt was a 5X10 matrix, this time potted with heat conducting potting in a FR6 tube, it lasted for one hour of testing.
The long thin tube is the voltage divider 1:1000, it seems to be a good one.

ballast vd.jpg

One success to report is the voltage control on the feedthrough, it is good.

convenient attach.jpg

I had made a squirrel cage grid with 9 pins in it, and this was for the sole reason that I wanted a spanking cool 9star picture as my future avatar, well that turned out to be a bad choise, at least since the axis pointed right at the viewport. I had some bad expectations beforehand, and for that reason I had put sacrifical glass in front of the viewport, this should prove beneficial.

9star.JPG

I got my nine star, but in the wrong place, as a blue reflection on the viewport, but what was worse, the front hole in the grid shou out a death ray directly on the glass, which got damaged.

cracked.JPG

You can see how the glass (quartz) got chips blown out of the surface where the death ray hit.


Ok, back to the lathe and make a new grid:


DSC_4802.JPG

This one showed out to perform better:


cool grid.jpg


and soon It got all red hot.

hot grid.JPG

If I could only figure out how others manage to catch theit fusor internals without all the haze, perhaps it is a photoshop thing

Cheers, Finn hammer
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Re: Finn Hammer, fusor update.

Post by Jim Kovalchick »

Finn,
Great looking plasma pics!

Regarding haze, fusors tend to look hazy until the chamber conditions through heating. I'm betting yours will look clearer soon.

Jim K
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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

Finn, Ive always had similar problems taking distance shots of the fusor and BoT. Seems that the autofocus latches onto the exterior hardware rather than the slightly more distant plasma within the chamber. My remedy was to place the camera right up against the viewport (using a makeshift insulator) allowing for focus on the grid or BoT target. Sometimes taking a video from the same distance will work better. Then it’s just a matter of taking a screenshot from the video.

Regarding the squirrel cage (SQ) I always wondered how folks kept the axis beam from blasting a divot out of the viewport. The latest videos of Dougs fusor display some great imagery of the SQ in action but there’s no evidence of any beam hitting the viewport. Quite possible there’s a sacrificial lens there but knowing the high power levels he ran I can’t imagine it lasting long. I also can’t imagine him cracking open his chamber all the time to replace it either. It’ll be interesting to find out exactly what he did.

The diameter of your new copper electrode appears to take up a bit of real estate within the chamber. I’m curious if you’ve noticed any problematic interaction with the chamber wall. One of the BoT targets I used which incorporated fixed magnet electron suppression was of similar size. Just big enough to cause a Paschens Law issue with the nearby chamber wall. I know BoT dynamics differ greatly from the fusor but I’ve had similar issues a couple years ago when experimenting with larger fusor grids.

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Mark, Jim

Regarding the photos, I am stunned. It is not an autofocus thing, I set the focus manually, by shining a flashlight on the grid, so I can see the focus well, camera on a tripod, lens is the famous 200mm Nikon Micro, sharpest lens available. But still there is that blue ionizing thing. I saw it in the big triodes on my single ended tube amplifier too, but not to this extent. I am considering to afd a grounded mesh in front of the sacrifical glass in the viewport.
Regarding the grid diameter, no problems as I see it, no flashovers to ground or anything like that. The first couple of minutes, there was a sort of sprinkling on the surface, as if small specks of dust provoked breakout, but were extinguished in the proces, that is all.
But mind you, I have no idea whatsoever, which diameter is the right one, or more suitable, I use the rule of TLAR ( That Looks About Right) and with my limited experience, that does not say much.
But I did go to the junkyard to get short pieces of stainless tubing in 15 - 22 mm range, and I am quick on the lathe, so many grids will be tested, as soon as I get a suitable ballast resistor. Those power mox resistors look tempting, to end all experimenting on that part.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Frank Sanns »

Great work on your setup Finn. Top rate.

As for the photos, it is not the camera or radiation. It is a dirty chamber.

Any fusor that is open to the air will have a fog within the chamber. It is outgassing.

If deuterium is added soon after the pump down, the color will look a bit ruddy. This color will clear up rather quickly but the haze can remain for the better part of an hour of operation or even for hours if the fusor was just assembled. Run longer and glow cleaning will clear things up and you will get tack sharp pictures.

The camera is more sensitive than the eye to the haze because of the longer exposure. You may no longer see it but with more light making it into the camera image, it will show up. A good indicator of how clean your chamber is. A necessity before you start getting good neutron numbers.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Jim Kovalchick
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Re: Finn Hammer, fusor update.

Post by Jim Kovalchick »

In addition to the chamber conditioning that Frank and I spoke of, the blue haze could also be your viewport glass fluorescing. Especially with that tube grid, as you noticed, there is a secondary electron beam hitting your glass. Borosilicate fluoresces blue.
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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

All good points. Jim, you me minded me of the UV fluorescence on my ion source. Finn, could this be what you’re seeing?

C4C6E860-7356-4A9C-AF04-F5E1038286FE.jpeg
C4C6E860-7356-4A9C-AF04-F5E1038286FE.jpeg (36.34 KiB) Viewed 12041 times

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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Great work Finn. I like the photos. Once you get a stable system with a good ballast, you can start smoothing out your operational experience that will become a natural function of your hands at the controls. once you are in the groove, you will become extremely sensitive to any sudden changes in operational characteristics. Smooth stability in startup and running is the goal. Early on, a fusor can be all over the place. Every time you open the system or change a grid, it is a whole new ball game, starting from scratch and having to get use to new characteristics.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Frank,

Thanks, good news if a dirty chamber is the reason, dince there is s remedy for that.
I had gotten sloppy with the chamber cleanliness, time to take it apart for a vigorous rubdown.

Mark,
UV flourescence sounds about right.

Jim,
The sacrifical glass is quartz, I forget whar the Lesker viewport has.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

The ballast resistor.
There are some chinese wirewounds that claim to stay within spec. both voltage- and powerwise, but given the urgency (which is, of course, more imaginary than real) and a bit of scepticism, combined with previous excellent experience with Ohmite's products, led me to the conclusion that there is really only one possible candidate for a ballast resistor, as aquired across the counter, and it is one out of the Power-mox series, from Ohmite.
Mouser has them, and the item shipped free from the US to Denmark, but then it is not exactly cheap either.
I have no doubt that it is worth every penny, now that it has been in my hands for a couple of days. This is what quality looks like:

Quality!
Quality!

Now, it does not come in the funky non-inductive style that "they" parade on their product page, because it is what we all would want if it was available,

Funky but non-stock!
Funky but non-stock!
Power_Mox_DSL.jpg (14.42 KiB) Viewed 10390 times

but apart from that, it is everything desirable, ceramic former, thick film resistive spiral and the coolest clear lacquer finish. And the 11 turns work out to 0.3µH, so what.....

Only complaint is the radial attachment lugs, I don't like them. Lots of sharp pointy edges, lots of places for corona to form. Corona, the dreaded mother of all arc discharges, the culprit of every surface track. Something had to be done, and what.. isn't that why I made that radius attachment to my lathe? so that I could whip up a nice couple of toroids in short order?
After another day in the workshop, this is what I had available:

IMG_20210606_101348.jpg

The toroids are mounted to the resistors collet style, not unlike some potentiometer buttons attach to the shaft (the good ones that don't mar the spindle with set screw marks) and some phenolic and FR4 trimmings to suspend the assembly.

The finished article looks like this:

DSC_4845.JPG
The rated power dissipation as I^2 x R losses is 50W, so it can support a continious current of 31mA to flow
The ballast resistor only sees the full voltage across the element for a brief flash in time, just when the arc strikes, otherwise the voltage drop is a maximum of 5000 x 0.031 = 158V,
(Edit: woops, should have read 50000, not 5000, for 1580V)
but the whole structure will be floating at whatever voltage I dare to throw at it, and since I don't want to use oil, and neither want it to arc to surrounding grounded parts, that is the reason for this litle exersize in field control.
The fact that it is also pleasing to the aestetic senses is only an added bonus.(Us seasoned tesla coil builders have an incurable, weak spot for toroids).

Cheers, Finn Hammer
Last edited by Finn Hammer on Sun Jun 06, 2021 1:53 pm, edited 1 time in total.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Even in a dangerous pulse of current the voltage across the resistor will not reach a level to arc running end to end on the resistor, the voltage is near zip. At a run current of 20ma you are looking at 1kv across the resistor. (50,000 X.02 = 1000volts) The resistor would internally arc band to band, (assuming zero supply impedance), long before it would arc toroid to toroid in a pulse condition.

Unfortunately, there is the real impedance of the supply thrown in, buckling the output voltage and the plasma arc impedance within the arcing fusor. This limits arcing possibility within in the ballast resistor.

Still, you have closed all possible doors with this overkill. Slick, polished insulation on flat surfaces accumulate dust to create paths not expected. Those toroids are awful close to that surface.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Richard,

You see it all.
The dust is one aspect that I had not given any consideration, and although the assembly is being mounted upside down, with the resistor hanging, there is no telling what electrostatic forces can do to throw dust upwards.
I may have to redesign the FR4 standoffs for more clearance.

Cheers, Finn hammer
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Re: Finn Hammer, fusor update.

Post by Dennis P Brown »

I submerged my ballast resistor under oil; fully synthetic auto oil since that is actually superior to many transformer oils. It not only electrically insulates it but dissipates heat significantly better than air.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

When checking out my x-ray transformer back in 2004 before installing it in the fusor IV rack system, I put my 63kohm, 100W ballast resistor in the tank with new HV silly cone diodes all in the oil. There it has resided for the last 17 years along with the diodes. Once pulling out the vacuum rectifiers and filament xfrmr back then, there was a lot of room for the new diodes and ballast.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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