Vacuum Electron Tubes Electronics Triode Part 2

Picture 1. 6J5 RCA Metal Triode

Picture 2. 6FQ7/6CG7 Medium-Mu Twin Triode

The 6J5 Medium-Mu Triode image in Picture 1, is an excellent specimen of the single triode in a single metal envelope. It was made for Class-A amplifier application and it has an amplification factor of 20. By 1968 it was a collectable specimen as the RCA Receiving Manual listed it as a discontinued vacuum tube.

Picture 2 demonstrates it with a 6FQ7/6CG7 Medium-Mu Twin Triode that two power triode can fit just fine into a single, miniature, nine pin, all glass envelope. Each triode has a four Watt power dissipation and an amplification factor of 20.

A seldom noticed or appreciated, but most important ingredient of any vacuum tube is the getter. The getter is responsible to remove residual gases after assembly and during the life of the tube. When the getter is flashed, it further increases the already high vacuum. Getters are in the form of a dark, shiny, mirror like, reflective deposit in the inside of the glass envelope, usually on top of the tube, far away from the electrode assembly.

Usual getter materials are often magnesium, barium, beryllium, zirconium and others may be used alone or in a mixture. A proper getter is inert and actively binding to gases and it is usually is in a powder form inside the washer like getter holder visible on top of Picture 1. Often getters act as "keepers" to be continuously active in binding to gases not only just at the time of firing.

Once the tube is assembled it undergoes many hours on the vacuum pumping until it is sufficiently evacuated. Then it gets heated to a high temperature to force all gases to boil off then the electron tube is sealed. After sealing is done, the getter is fired by electrical induction method.