If you like your VR valve glowing in the dark but you’re concerned about how quiet it will be, then you may be interested in this post.
I like the VR, I used them a lot. They are quieter than most people claim. However, they’re not the quietest if you’re looking for the lowest noise level.
Below is a very simple circuit which you can implement easily and use your lovely VR valves glowing in the dark! The VR (U1) is fed from the HT source via R1 .R1 should be sized to at least provide 10mA to the VR valve. C2 is the maximum allowed cap. R2 and C3 form the cap multiplier section. R2 isolates U1 from C3 to ensures it doesn’t oscillate. C3 to 10uF can provide about 50dB reduction at 100Hz, so great to smash out any remaining noise from the VR. Q1 provides current limitation in conjunction with R4. This will protect M1. The output is about 5V lower than the VR level. Well, that’s what you pay with a follower or cap multiplier.
The PSRR of the cap multiplier below is about 110dB @100Hz. Great performance:
The source follower PCB can be twicked easily to use for this purpose. It can also be used as an electronic choke (aka gyrator) and or a simple cap multiplier.
Q1 can be a BC547 thanks to the protection diodes D1 and D2 (15V) which will prevent from exceeding VCEO levels.
I’d use this circuit in many configurations, not just the screen supply.
