We can adjust the level coming into our first stage with this simple volume control. It works when the input signal goes through the Potentiometer which controls the resistance to ground, when the resistance is high the volume will be at it's maximum depending on the resistance used, and when it is at its lowest next to 0 ohms this is where the signal will be fully down to ground.

You could get away with just the Potentiometer but the added resistor, this is for and dependant on the input impedance of what it is going into since it will be a vacuum amplifier in our case we could try 100k, if it has too much attenuation then you can drop it down to a 47k or even down to a 10k.

As for the Potentiometer we can either use 100k or 500k, 100k would interface better between both solid state and vacuum tube equipment, since we want to add more circuits to our project and we may be adding some solid state circuits we will choose the 100k Potentiometer.

HOW IT WORKS

The input signal simply comes in through input pin 3, if the potentiometer is at its maximum the resistance is high and the volume will be at its maximum minus the resistance of the potentiometer and the resister after,