This months tube is one of the very last developments of the vacuum tube era. A tube which was made for the regulation of the high voltage in color TVs. The 6HV5A.
The 6HV5A is a beam triode. It is very similar to the 6HS5 which was already presented in the tube of the month series almost two years ago. Pinout and most of the technical parameters are the same between these two tubes. So I won't repeat all the technical details.
The 6HV5A has a slightly higher max. plate dissipation which brings the drawback of also higher heater current. It is physically a bit larger to allow the 5W extra dissipation. A comparison between Sylvania 6HS5 and 6HV5A:
Since also the usage of this type of tubes was extensively covered in the 6HS5 article, I will not repeat that but rather allow a closer look to the construction of the tube.
During the manufacturing process the tube got evacuated through the little glass stem at the bottom:
Removing the glass to get a better view of the construction details:
The three rings held the getter material which was flashed after evacuation of the glass bulb. The electrodes held in place by the two mica discs at either side. The beam forming plate is visible through the rectangular holes:
The heater wire entering the cathode sleeve:
The heater wire ends are welded to the pins:
The heater wire partly removed from the cathode:
A close up of the heater :
Heater completely removed:
The plate, removed from the rest:
The beam plate, grid and cathode assembly:
This photo gives already a hint of the remarkable grid structure. A close up:
Zooming further in:
Removing the beam forming plate:
Beam plate, grid and cathode separated:
The beam forming plate:
A close up of grid and cathode ends:
This photo shows the scale of the structures:
The grid pitch:
Let's have another look at the magnificent grid:
Here we see how the grid wire is soldered (or welded?) to the grid rod:
View from the top side:
This tube is a fine example to show how far the vacuum tube technology was evolved before it got abandoned.