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RE: [TCML] Re: VTTC Sound Generation
Jim,
I have two plate supplies in my VTTC: http://www.drspark.org/Teslathon2008.htm One has the 1/2 wave AC "level shifter" with four 1uf / 2200volt series capacitors, which I use for the "sword" type sparks (If the primary and secondary looks familiar, I swiped them from Dr. Spark.....yep; that's him looking at it as well!) the level shifter supply uses a huge MOT out of an old oven.
The smooth DC supply uses twin identical MOT's that are full wave rectified. I am able to run up to 3.4kvdc into the plates at about 800ma. (Adjustable overcurrent circuit trips plate circuit off here to protect tubes) I tried using 1/2 wave with clean audio input (also CW mode), but had pretty bad 60~ carrier with the sound. You really seem to need clean DC full wave rectification for good audio, but this comes at the expense of spark length, as this mode is a real power hog. I have the ability to quickly connect a real plate xfmr to the circuit, but have not tried that as yet. I do intend on trying this sometime as I noticed quite a bit of line input current draw with the MOT's. I have saturation tested several MOT's and found the IEEE curve to be consistently around only 38~42 volts! This is terrible as far as a "plate" xfmr is concerned, but I seem to be getting enough output power for my experiments.
In conclusion I would highly recommend full wave rectified DC for the plate supply if you were to use CW AM mode. I also use this mode for connecting the Theremin and keyboard to the VTTC..........kind of sounds like a miniature DRSSTC! In this example, I am using our Audiotesla MKIIc controller to modulate the VTTC as seen in the prototype video: http://www.youtube.com/watch?v=5K41aPR2bKg
I think the plate xfmr would give you less line current draw with the higher plate voltage, particularly at an "idle".
Woo
> [Original Message]
> From: Jim Mora <wavetuner@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Date: 6/1/2008 6:11:28 PM
> Subject: RE: [TCML] Re: VTTC Sound Generation
>
> Hi DocHank,
>
> Have you or others used fullwave rectification on say a 4 or 5KV volt plate
> transformer. I seem to remember someone writing the doubler gives it a
> better shot in performance. I would think a Plate transformer would be
> better for audio modulation for us old timer heavy iron types :-^) I believe
> John Freau has commented on this.
>
> I have (4) RCA 833a's and original Johnson sockets, top caps, and plate and
> grid heatsinks. I also have rat-holed a couple of Big mica Sagamo, white
> transmitter caps and other classic micas.
>
> When I build this one, it will use a nice piece of furniture and be a
> tribute to my Dad who got me interested in electronics at 7 years old by
> building a crystal radio and a board with a light, bell, knife switch and
> completed circuit around the board to a battery - cool thing to do for your
> kids!
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of dr.hankenstein@xxxxxxxxxxxxx
> Sent: Saturday, May 31, 2008 7:47 AM
> To: James Zimmerschied
> Subject: [TCML] Re: VTTC Sound Generation
>
> Jim
>
> First of all, I am assuming you are using a MOT with or without a level
> shifter on your VTTC. (That part doesn't really matter) and you are
> obtaining good sparks in CW mode, but when you connect the Staccato
> controller to the circuit, the sparks are "wimpy"? Maybe you have even
> adjusted the "duty cycle" control to no avail? The duty cycle control also
> seems to act like a "phasing control" and not only tells the tube how long
> to stay on, but when to come on. The tube can only conduct during the
> positive part of the wave, so if you try to turn it on at the wrong time
> (such as during the negative portion of the cycle), it simply won't conduct,
> or if it does, the output will be very wimpy at best. Maybe it's just a
> phasing problem:Try reversing the staccato controller supply transformer's
> leads. This will shift the pulse phasing 180 degrees and the run the duty
> cycle control through it's paces. Also, I have noticed that some of the
> staccato schematics out there do not provide en
> ough duty cycle when built as shown. You may want to play around with
> that. Still others have "bust mode" and other sorts of bling which I find
> totally unnecessary.
>
> Personally, I am using a 40amp / 800volt SCR. I have used a 40amp / 600volt
> Triac with the same output results. However, if using an SCR, you need the
> swamp the gate to kathode with a 390ohm-1/2W resistor in parallel with a
> .01uf ceramic cap and the series-limit the 12V pulses from the Steve Ward
> board with about a 100~150 ohm resistor to the gate. You'll have to
> experiment with this value for consistent results. I did notice, if using a
> triac, you can get away without any resistors or caps at all.
>
>
> ----- Original Message -----
> From: James Zimmerschied
> To: dr.hankenstein@xxxxxxxxxxxxx
> Sent: 5/30/2008 9:19:16 PM
> Subject: Re: VTTC Sound Generation
>
>
> Woo,
> Thanks for the information on the sound source. I am using Steve's circuit
> but I don't get a very strong signal off the triac/scr. I may have a bad
> solder connection somewhere. What SCR type are you using?
>
> Thanks
> Jim
> ----- Original Message -----
> From: dr.hankenstein@xxxxxxxxxxxxx
> To: James Zimmerschied
> Sent: Monday, May 26, 2008 1:33 PM
> Subject: RE: VTTC Sound Generation
>
>
> Jim,
>
> What circuit are you using that is giving you problems with the staccato
> circuit? If you are using the "Steve Ward" design, you shouldn't be having
> any issues as this is a pretty straight forward design. As far as grid
> driving goes, I am using an oscillator/modulator/mixer in the front end and
> feeding the low level signal into a mosfet 100 watt 30~500khz power
> amplifier which drives the grid via a coupling transformer. Of course, the
> grid must be properly biased to prevent the tube from excessive current
> draw. At present I am working on a positive feedback circuit with phasing
> control from the coil's secondary to the oscillator's input to improve
> issues with oscillator drift. Unfortunately, work has gotten in the way of
> my fun, so the project is on hold for now.
>
> Woo
>
>
> ----- Original Message -----
> From: James Zimmerschied
> To: dr.hankenstein@xxxxxxxxxxxxx
> Sent: 5/23/2008 7:01:36 PM
> Subject: VTTC Sound Generation
>
>
> Dr H,
> do you have any circuit information for coupling a sound source to the VTTC
> grid? I have a VTTC and have had trouble getting the staccato circuit to
> work correctly. I am assuming the sound source intermittently grounds the
> grid.
> Thanks in advance.
> Jim Zimmerschied
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