Emperor-TK
Well-known member
Jakob, I'm using the G9 power supply for another project and ran across a couple things I didn't understand. When I built my G9's, I was more-or-less following a "recipie", but now I am getting a little deeper into the design aspect.
1) You suggest using 35VA transformers for both values. Is there any reason that the second step up transformer needs to be this large, since the HT plate currents wil be relatively small?
2) How did you choose the resistor values for the TL783 regulator? I see from the TL783 data sheet that the ratio of the parallel and shunt resistors determines the Vout. R1=517 and R2=100K (2W). How did you choose these values and not a different multiple of the same ratio? How can you determine the current draw in advance in order to specify the resistor wattage?
The reason that I am asking is because I am changing the design slighlty. I want HT=220V, so I plan on changing the paralleled resistor pair on the TL783 to 570 ohms from 517. I am also replacing the 12V regulator with an LM317 for 6.3V heaters. I plan on doing 330 ohms and ~1330 ohms (with a 1.25W trimmer), but these values are chosen nearly arbitrarily. Does this sound OK? The data sheet shows and example using R1=240 ohms, R2=5K trimmer, which is where based my starting point.
Any design guidance would be appreciated.
-Chris
1) You suggest using 35VA transformers for both values. Is there any reason that the second step up transformer needs to be this large, since the HT plate currents wil be relatively small?
2) How did you choose the resistor values for the TL783 regulator? I see from the TL783 data sheet that the ratio of the parallel and shunt resistors determines the Vout. R1=517 and R2=100K (2W). How did you choose these values and not a different multiple of the same ratio? How can you determine the current draw in advance in order to specify the resistor wattage?
The reason that I am asking is because I am changing the design slighlty. I want HT=220V, so I plan on changing the paralleled resistor pair on the TL783 to 570 ohms from 517. I am also replacing the 12V regulator with an LM317 for 6.3V heaters. I plan on doing 330 ohms and ~1330 ohms (with a 1.25W trimmer), but these values are chosen nearly arbitrarily. Does this sound OK? The data sheet shows and example using R1=240 ohms, R2=5K trimmer, which is where based my starting point.
Any design guidance would be appreciated.
-Chris