[TCML] Re: VTTC Sound Generation

["" <dr.hankenstein@xxxxxxxxxxxxx>]

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 enough 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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