Tube DIY Asylum: RE: Ops! I did it again! by Gary P

Hi,

R3 is used to increase the output current before the current limit circuit kicks in.

How much current is your phono preamp going to draw? I suspect that with a phono preamp you do not need to install R3.

Without R3 installed the circuit will be good for ~150ma without the current limit activating. With the values shown in the circuit and the output voltage set for 100V the circuit will source ~400ma before the current limit activates.

To set the current limit to ~400ma at different voltages you adjust the value of R3 so there is ~.42ma current flowing at the desired output voltage.

Keep in mind that as this voltage regulator does not use a large output capacitor, the current that the current limit circuit sees will be the bias current + the peak signal current.