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Our Vacuum-tube coil

Preliminary planning for two small vacuum-tube coils

• Tubes: I now have an 811A, a VT127, a 4-400A, and a 6LR6. I dunno what will get used first.
  The specs the 811A are:
• Plate-1500V, 65 watts dissipation, 175 ma;
• Grid-50 ma;
• Filament-6.3V, 4 amps.
  the specs of the 6LR6:
• Plate.......
• I did have access to a pair of 5514 triodes, each capable of 65 watts, but chose top not use them for they are rare.
• Transformers: I want to remove some windings from the secondary of one of my MOT's, and for my purposes they should provide more than enough current.

  

  I could have had perfectly matched plate and filament transformers to power a pair of 5514's.... : (

• Circuit:

• Well...something like this... but I'm really not so sure about any of the values yet. This may interest you. It is a simple way to foolproof your setup, so that the plate current is never applied before the filaments are energized.
• Secondary: I have an idea to try to use this conical (~10^o off the vertical) form, though it presents some interesting engineering problems.
  
  As I used the wire I currently have, 24 gauge, I estimate the resonant frequency to be somewhere between 1.2mhz and 1.8mhz... ...and that's pretty high for a tesla coil.
  Probably, I will use a 3" X 15" secondary of thin wall PVC.
• Primary: For the more conventional style, I'll use a section of 5" or 6" PVC, and wrap the plate and grid coils on the same form.
  Because of the high frequency at which the conical coil will operate, this will need to be as small as possible... ...which means really tight coupling to the secondary. If I find a readily available suitable adhesive (i.e., oil-resistant), I plan on making the coupling just so tight that I'll need to submerse at least the bottom end of the secondary/primary assembly in oil. As the secondary will be slanted, I plan on cementing several vertical plastic pieces directly onto the bottom fourth or so of the secondary, and wind the primary directly onto that.
• Terminal: A steel point? A small sphere? A small toroid?

Audio Modulation! I will be trying this with the 811A, or may be the VT-127b or 4-400A driven coil.

The idea is simple enough, modulate the grid by putting the secondary of an "audio transformer" in series betweeen the grid and grid-leak bias. The only trouble is finding a suitable transformer with a primary impedance that matches the audio amp giving you your signal. Otherwise, you will hurt the amp. But, it's really not that hard! A little experiemntation and some trial-and-error, and I should end up with some singing, talking, (ahhh, Pink Floyd AND plasma, I'm in heaven!) streamers!

The most important feature of the circuit is that it must be running on smooth, filtered DC, rather than the AC most often used. This affords continuous operation, rather than the 60Hz pulsed operation from using "raw" AC (only one half the AC signal is shown since the tubes used will act as rectifiers, conducting in one direction only), or even the 120Hz pulsed operation from unfiltered, full-wave rectified DC.

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email: electrophile@juno.com