Monte McGuire
Well-known member
- Joined
- Jul 26, 2013
- Messages
- 384
I'll second the Zener over voltage recommendation. The regulator can handle only 125V volts from input to output, so you need to clamp that. Related to this, a simple way to prevent similar problems at startup is to make sure that the caps ahead of the regulator are larger than the capacitance after. This way, the output won't take too long to 'come up', possibly generating a lethal drop across the regulator.
As was mentioned, when using the regulator at such high gain, the ripple and regulation gets worse just because of the finite loop gain in the regulator. One way to solve this issue is to replace your 100KΩ variable adjustment resistor with a string of a few zener diodes and a smaller variable resistor. In this way, your regulator's reference input 'stands on top of' the zeners, so the regulator can run at lower gain, giving you better ripple rejection and lower output Z. Since the zeners are biased by the regulated output, they're fairly stable and quiet. In fact, the adjustment node should have lower impedance with the zeners than without them, so the noise there is lower, and the noise gain of the regulator is lower too.
Finally, a lot of tube circuits have very low PSRR, nearly zero in many cases, so quiet B+ is useful. Sure, RC filters work too, but so do regulators. You can take your tradeoffs… use a cap that may dry out or a regulator that may fail. ;-)
As was mentioned, when using the regulator at such high gain, the ripple and regulation gets worse just because of the finite loop gain in the regulator. One way to solve this issue is to replace your 100KΩ variable adjustment resistor with a string of a few zener diodes and a smaller variable resistor. In this way, your regulator's reference input 'stands on top of' the zeners, so the regulator can run at lower gain, giving you better ripple rejection and lower output Z. Since the zeners are biased by the regulated output, they're fairly stable and quiet. In fact, the adjustment node should have lower impedance with the zeners than without them, so the noise there is lower, and the noise gain of the regulator is lower too.
Finally, a lot of tube circuits have very low PSRR, nearly zero in many cases, so quiet B+ is useful. Sure, RC filters work too, but so do regulators. You can take your tradeoffs… use a cap that may dry out or a regulator that may fail. ;-)
