ASSEMBLY:
The
tube's internal electrode system is assembled in a clean-room
enviroment. The components are made from pure materials and manufactured
with high precision (+/- 0,02 mm). Before assembly all parts are cleaned
in an ultrasonic bath and de-gassed in a reducing atmosphere. The
control grid is gold plated, the screen grid is plated with copper and
graphite. Specially designed fixtures are used during assembly to
prevent electrode deformation. Spot welding is used to electrically
connent the internal subassembly to the contacts of the tube base. A
complete mechanical and electrical inspection is performed on every
system.
SEALING:
The
tube's internal systems are thoroughly cleaned again and inserted into a
clean glass envelope. The envelope is then hermetically sealed to the
base. The seal between the envelope and the base is thermally stress
relieved (tempered).
EVACUATION:
Assembled
tubes are evacuated on an automated pumping machine with mechanical and
diffusion pumps. During this process, the cathode is electrically heated
and its emission substance is activated. All internal parts are heated
by high frequency coils, the getter rings are ignited absorbing the
residual gas inside the tube. The final vacuum reaches 10-6 Torr - the
level required for proper tube operation.
STABILIZATION BURN-IN
The
evacuated tubes are equipped with sockets. The cathodes are activated
and the electrode's potentials stabilized in a special burn-in unit.
Here, the tubes are exposed to electrical conditions reaching up to 300%
of the nominal operating levels.
TESTING:
Every
tube is electically tested for parameters such as isolation
characteristics, the electrode's current levels covering the entire
operating curve, the condition of vacuum, cathode emission capability,
filament voltage and current levels. A microphonic test is performed on
every tube. All tubes are then further burned-in for a period of 24
hours at the nominal specified operating voltage and current levels.
Every month, a random sample is taken from the production to perform a
life test of 5000 hours at nominal operating conditions or 1000 hours at
maximum specified levels.
