SImple Valve (Tube) Tester

A valve tester is nothing more than a set of adjustable calibrated power supplies, a meter to measure to current and a set of sockets into which the valve under test can be inserted.  However when I started to look for a second valve tester I found them incredibly expensive, I therefore decided to make one.

The valve tester shown here has an adjustable HT supply (upto 300V), an adjustable negative supply for grid bias (upto -50V) and a  heater supply.

The HT supply is just a simple cathode follower, based on a circuit from Radio Constructor by G A French.  Initially I was going to have a switch on the voltmeter to monitor grid voltage as well as anode voltage but in practice it was easier to use my DVM.

I used valve data for an AVO valve tester when testing valves, any valves that required a heater voltage other than 6.3V I used a seperate power supply.  The EL81 is also overrun with some valves, this has not caused a problem.  In use I manged to damage the milliammeter due to faulty valve, I plan to put a diode across the movement in future to help prevent this.  I also found that the odd valve would oscillate at high frequency.