Here is a quick test of a russian СГ2С (SG2S) 75V voltage valve regulator:

The CCS is a classic cascoded DN2540 MOSFET. A russian PIO capacitor is bypassing the regulator and the input impedance is the Pete Millet’s interface impedance. HT is a well regulated variable power supply.

When near maximum bias current is achieved (circa 30mA), the noise floor is surprisingly low: -85.5dB / 53uV.

Need to capture input of power supply at the CCS input 🙂

Edit: after measuring the power supply noise level and finding that is near -90dB, came up to the conclusion that the above noise level is the VR noise. Quite good for a simple (but effective) voltage regulator. Gary Pimms used this configuration many times on his designs…

Update

Upon request from Vyacheslav, here is the noise analysis for different current points:

As you can see it’s very linear. There is a 4dB difference between 5mA and 40mA.

Also tested ripple attenuation using a poor-regulated HT power supply. Here are the interesting results:

• 62dB @50Hz
• 80dB @100Hz