Some Russian data sheets show the GS-35b’s anode cooling requirement
to be 2500 liters/minute. Other specification sources include information on the cooling
requirements of the tube’s cathode and grid. By definition, one cubic foot equals 28.327
liters. Converting to cubic feet per minute (CFM), the anode cooling requirements are, then,
about 88.3 CFM.
Refer to the airflow diagram to the right. In
this amplifier, the under chassis area is pressurized. A number of screened airflow holes are
placed in the grid compartment and main chassis mounting area. An inspection of the photograph
for the grid compartment will show some of the eight one inch diameter screened inlet air
paths. Two 2.5 inch diameter holes in the top chassis plate provides an air path towards
the bottom of the tube radiator. Providing a large airflow surface as possible will reduce
the back pressure requirements of the external air blower fan. Passing all of the airflow
directly through the under-chassis shielded grid compartment will easily satisfy the cathode
and grid cooling needs. Some light duty requirements will allow a smaller blower to be used.
The only certain way to know the tube is being adequately cooled is to measure the tube seal
temperature to insure compliance with the manufacturers maximum specification.
It is very important to not ignore the
smaller cathode and grid airflow cooling requirements. The table below shows GS-35b element
cooling requirements in various units of measure:
