electricwestern.com

A number of successful Phantastrons have been built and even modded. I’m so happy.

We still have tubes and parts in stock for 6 kits, then it’s reorder time…

Thanks to everyone who has ordered so far!

L

Collin Cunningham of MAKE magazine is currently building a Phantastron and making some amazing photos in the process to document.

His Flickr account showing the Phantastron Build is at:

More photos including amazing close ups at:

http://flickr.com/photos/collinmel/sets/72157608315546923/detail/

I’ll gear up to post all my schematics on tube power supplies and such, but I just want to mention one amazing part:

PTC (Positive Temperature Coefficient) 

I use these, AND a traditional fuse on the 104V power supply line of the Phantastron. What’s so cool is that they protect you and your gear, but ALSO protect against stupid mistakes as well. (we all make them). The PTC in the Phantastron shuts the flow of electricity when current exceeds 50 ma. That allows the tubes to have more than enough power, but prevents a dangerous shock from getting through.

Furthermore, to "white-box" test, I hooked up the 104V supply to some tube heaters (usually the best way to hurt a tube and a power supply). The PTC kicked in and the current reduced to nothing in a blink.

Of course, if there is a fast surge I also have a 100mA fuse that completely cuts off the supply on the phantastron. However, in all my fiddling, I have yet to blow a fuse due to the PTC.

The best part: after power is removed, just wait 30 seconds and everything is perfectly normal again – the PTC resets!

Lorin

Electric Western is busy packing Phantastron kits and electric noisemakers of all sorts into our tiny vintage trailer for a trip to the Maker Faire in Austin! So, since we’re leaving on Wednesday the 15th, we’ll be temporarily out of the shop and unable to ship for about a week. If you desperately need a Phantastron kit RIGHT NOW please order by Tuesday, because we won’t be back until Wednesday the 22nd.

And if you’re in the Austin area Oct. 18-19, drop by the Maker Faire and check out our booth… we’ll have dueling Phantastrons, tube theremin demonstrations, a steam-powered synthesizer, and more!

So, indeed, the Phantastron used as a radar circuit and integrator is a not very common, or find-able on the Internet. So, here are some resources if you want to mess with this great old circuit yourself…

Here’s the description from Samuel Seely’s 1950 book, "Electron Tube Circuits"

The Phantastron.

The phantastron combines the Miller
integrator and the trigger properties
of the sanatron in a single tube. The
schematic diagram is given in Fig. 19-30,
and the significant wave forms at
several points in the circuit are given
in Fig. 19-31.

Owing to the mutual effects that exist during the course of its operation, the phantastron in the
form shown is somewhat inferior to the sanatron. It is for this reason
that during the Second World War the British, who devised both circuits, preferred the sanatron.
The American version of the phantastron is designed around the 6SA7 heptode, which, owing to the mutual shielding between significant elements, proved to be entirely satisfactory. One version of the circuit is given in Fig. 19-32. A second variation of the basic circuit is given in Fig. 19-33.

       What makes a radar circuit inferior, might make it superior for a synthesizer or audio circuit. Using a pentagrid converter does create a more linear sweep (or a sawtooth), but it also eliminates some of the unique feedback and leakage effects you get with a pentode. In my opinion, creating a more perfect linear sweep with a vacuum tube is an accomplishment, but may be approaching an area where a silicon opamp would create the same tonal quality — thus eliminating the exaggerated soft clipping and warmth of a vacuum tube circuit. 

    I selected a 6SJ7 pentode for the Electric Western Phantastron to maximize the resonant harmonic qualities (which could be viewed as "inferior" in radar). The 6SJ7 is an excellent pentode, essentially the "inline" version of the 6S7 (which has a grid cap on top). The 6SA7 was used in much touted RCA and ampex pre-amps of the 1940s and 1950s. I know, I’ve worked on those machines as a tech, and yes, they’re metal jacket tubes, and no, that doesn’t make them inferior. In fact, pointing at the early Fender amps of the 1950s, many people believe the metal jacket 6SJ7 was superior in sound to other variations (a 6au6 and 12ax7). Regardless, the 6SJ7 is a lovely vacuum tube, one of my ideal pentodes, as I can get it to do almost anything, it sounds good to me and it has a really nice gain. The 6au6 is comparable miniature based tube, if you are so inclined.

    Looking at figure 19-30, you can see two diodes are used to stabalize the signal. Not a bad idea, but not altogether necessary, unless you want a more linear circuit. So, simply concentrate on biasing the tube properly and tap the output using a metal film capacitor to remove the DC. The reason the diodes are there is to provide some separation of the outputs and hold the waveforms at their potentials as long as possible — which can be good and bad. I did try a 6H6 dual diode to good effect on the Seely circuit, but I prefer the capacitor coupled version as it is hotter, louder, and gets results without the need for another tube.. At some point, I will lift the hood on my test phantastron and try some silicon or germanium diodes to isolate and mix the signals.

    So how do you set up the basic Pentode circuit? Well, you could get a Phantastron Kit! That is how I make my living and support research into these things. So, get a kit and modify modify modify, that’s why I put extra turrets in it and space for more tubes.

    I will explain how you set it up, though, for the seriously DIY oriented or those too poor to support my new business:

    The plate should have reasonable current from the 100 to 150V power supply  — a 100K resistor works. In my case, I pulled up the screen with a 33K resistor, which works. Regardless, the screen Voltage should be near the neigborhood of the plate voltage. Now, the Grid is the trick, you need to control the current here, so the potentiometer should be abot 2M and a series resistor of 470k should be added to prevent the plate voltage from hitting the grid when the 2M pot is open. This setup runs rather hot, and supplying the plate with less current (using a larger resistor) would decrease the leakage, feedback gain, etc. But, again, I’m in it for feedback, leakage and non-linearity.

    Regardless, a 100V,  15 Ma plate supply is enough to breadboard with. Keep trying different voltages and listening to the changes as music, pulses or other signal is fed through. You know it’s not in Phantastron mode when you just get a gritty pulsed distortion — keep tweaking — once the potentials are right, the plate, screen and grid dance in opposing phase and it really sings!

    Next entry maybe I’ll talk about some tube flip-flops and other integrator and differentiator circuits in relationship to the Phantastron. In the meantime I’d really like to see someone try this out in a really new way and send me a link. Perhaps the 6SA7 or another pentagrid converter, but try using the suppressor and not just tying it to the cathode as shown above. Or what about tweaking with the two screens that isolate the control grid. There are many possibilities.

    I will suspend your anticipation on one issue, though. The three waveforms produced by this circuit are out of phase with each other, so don’t try to mix them together – it’s disappointing, even with an active buffer. That’s the price you pay for 3 nice grids in one vacuum.

    Or just buy my kit and mod it. You won’t be disappointed.

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