Reading through the DIYaudio threads and a little own experience it looks as if shunt regulators really excel in ripple rejection and ‘subjective’ music quality. There are some proven designs, like Salas SSHV, still these don’t do ‘high power’ demanded by output stages. With the availability of high powered tubes for little money (like 40W GU50 for some USD) I am willing to experiment with ‘high power’ shunt regulators.
For example a PS capable of 300V at 220mA, with 160mA to feed 4 EL84 output tubes and a spare 60mA through the shunt tube, a triode strapped GU50. For CCS I am thinking about Gary Pimm’s CCS. I understand that if there is no load on this PS the GU50 will burn 220mA * 300V = 66W, which is more than max plate dissipation, but seems this tube can take this (even more) for short whiles. As such I know that shunt regulators produce additional heat, but that is nice for the winters when I am back in Europe.
I attach a proposed schematic for this regulator, and this is really the part I need assistance. A differential pair fed from a ‘negative’ regulated negative supply (since I read 4th edition of VA I already know how I will make this one) supplies the differential pair. Reference voltage is taken from a potential divider (R1 and R2) and control voltage is developed over R3. R4, R5 and P1 sample the output voltage, R6 is tail resistor (is a CCS, maybe LM334, also needed if it is about DC?).
If B+ voltage goes up, V on base of T2 increases, T2 conducts more, thereby T1 conducts less, less voltage is developed over R3, grid of shunt element comes closer to zero, shunt element conducts more, reducing B+ voltage.
Questions:
- Do you think it will work?
- What about using some HV bipolar transistors (MPSA 42, if I am not mistaken). How does ‘base current’ impact performance? Or better use a Vref (like TL431) instead of R1?
- Some decoupling needed, for better performance and or stability? Speed-up capacitor from B+ output to gate of T2?
For example a PS capable of 300V at 220mA, with 160mA to feed 4 EL84 output tubes and a spare 60mA through the shunt tube, a triode strapped GU50. For CCS I am thinking about Gary Pimm’s CCS. I understand that if there is no load on this PS the GU50 will burn 220mA * 300V = 66W, which is more than max plate dissipation, but seems this tube can take this (even more) for short whiles. As such I know that shunt regulators produce additional heat, but that is nice for the winters when I am back in Europe.
I attach a proposed schematic for this regulator, and this is really the part I need assistance. A differential pair fed from a ‘negative’ regulated negative supply (since I read 4th edition of VA I already know how I will make this one) supplies the differential pair. Reference voltage is taken from a potential divider (R1 and R2) and control voltage is developed over R3. R4, R5 and P1 sample the output voltage, R6 is tail resistor (is a CCS, maybe LM334, also needed if it is about DC?).
If B+ voltage goes up, V on base of T2 increases, T2 conducts more, thereby T1 conducts less, less voltage is developed over R3, grid of shunt element comes closer to zero, shunt element conducts more, reducing B+ voltage.
Questions:
- Do you think it will work?
- What about using some HV bipolar transistors (MPSA 42, if I am not mistaken). How does ‘base current’ impact performance? Or better use a Vref (like TL431) instead of R1?
- Some decoupling needed, for better performance and or stability? Speed-up capacitor from B+ output to gate of T2?
