Theory of operation

As low voltage is applied to the valve heater filaments, they will begin to glow red. After a while the heaters will heat up the valve cathodes, causing thermionic emission of quantum free electrons, which will form an electron cloud around the cathodes. These electrons form a space charge area, and the positive potential applied by the tester to the surrounding anodes will cause the electrons to migrate across the vacuum within the valve envelope. This will be observed as a gentle blue glow, which will gradually intensify until maximum emission rate is reached.

This blue glow is completely harmless, provides an interesting visual demonstration of quantum physics actually happening, and proves that the valve installed in the tester works! (Unfortunately it doesn't tell us too much about the sonic quality of the valve - you will have to put it in an amp and listen to it for that.)

It also makes a really neat desk-top ornament or paper weight!

Please contact us for pricing and availability.