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I am now looking for an audio transformer with 2:1 ratio. Checking my junkbox right now.
Here is the proposed circuit. The capacitve coupling seemed to work okay with anticpated waveform. And the circuit almost achieves the convergence required with insufficient at 350v p-p. I suspect if I can get 450v to 500 v p-p that will do it. I like the capacitive coupling with the resistive division. Focus is good across the screen. And the capacitive coupling means the transformer does not have to stand up to the brutal 3 to 4 kV. And is the mosfet needed at all? Maybe the transformer only? Last edited by Penthode; 01-27-2024 at 02:21 PM. |
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“Is the mosfet needed at all? Maybe the transformer only?”
Almost back to the original design but with the transformer isolated from the hv with a capacitor and a resistor divider.... why not? What was the ratio of the original transformer? jr |
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The original transformer was 10:1
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Can't you find a 10:1 transformer of the same physical size no matter what it's original purpose was, and stick it in there.... (Insulation should be compatible with the voltage in the circuit of course...) Maybe you have to add a cap across pri.or sec. to raise, or lower output as needed by tuning it with the cap..... Might even be a good idea to get a 11:1, or 12:1 that way you can attenuate output down as needed, easier to do than ending up with a signal too small from a poor match with 10:1. For that matter an LC circuit in your mosfet circuit output might just get it to "ring' a little higher p-p and do the job..... It's a nice circuit you made, I was wondering what you were going to do about the phase shift in your circuit when you first posted it.... Anyway - Interesting poop..... .
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Yes you can call me "Squirrel boy" Last edited by Username1; 01-27-2024 at 11:56 PM. |
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After a couple of months hiatus busy with other projects. I am returning to the CT100.
If you recall. my circuit worked well but there was insufficient amplitude. I gave up looking for a suitable audio transformer to step up the signal. Looking for a more efficient and less expensive approach, I have decided to increase the B plus to the FET in order to get a greater voltage swing on the drain. There was more than enough gain as the convergence controls would drive the FET output to clip the convergence waveform parabola. Looking at Digikey and Newark, there is a large array of 1000v plus power FETs which exhibit the linearity and provide the signal gain. To boost the drain supply I will experiment with using a standard 300mA filament transformer in reverse. I will tap into the 6.3 vac filament line to step up to 230vac and use a simple bridge rectifier. The current demand is very low which means only very simple filtering is required. A bridge rectifier will yield about 320volts DC which I will stack on top of the +400v supply. The new diagram with the stepped up drain supply is attached. Last edited by Penthode; 04-22-2024 at 10:12 PM. |
Audiokarma |
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Cool idea with the xfmr. As a young kid, i used to use two 6V doorbell xfmrs back-to-back for isolation to make B+ for projects.
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Hmm. I am boosting the B+ and I see the boost B+ on the CT100 is 680v. I am going to investigate using it for the FET. Would only require at most a resistor and capacitor....
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Here is my latest further simplified itteration. I will grab the B+ boost from the flyback transformer. The FET will be picking off about 3mA which should be relatively inconsequential. The 650VDC available as a supply to the FET drain should allow a nearly 600v p-p swing which should be adequate to provide the vertical convergence.
See the attached drawings for the modified circuit and the B+ boost source. |
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