DOUGLAS SNOWDEN wrote:
I have seen 3-500Z tubes mounted in the johnson ceramic sockets. The Heath
SB-220 uses them.
Will the 4-400 tube handle the airflow the same way? Usually you see the air
system sockets used so that the air will flow up through the bottom. Will
the filament connections remain solid in a 275 ceramic socket with a muffin
fan blowing across the tube?
? I have seen the sockets raised a bit so that the filaments get cooling.
Just wondering if the 4-400 would work that way as well? Any experience
with this?
=========================================
During the late 1970s ,the old 405 lines TV system in the UK operating
in Band 1 (approx 45 -65 MHz) was decommissioned and some equipment
landed at junk sales held at radio clubs . I managed to obtain two 1 kW
amplifier racks (out of 7 released from a local 7 kW TV repeater )

The rack had 2 QY4-400 (tetrode)valves with the (flat,ceramic) sockets
fitted approx 12 mm below the chassis on stand-offs . The space under
the chassis was fully enclosed (almost air -tight) and was fitted with a
pressure switch (with a large diaphragm to sense and switch a low pressure).
A centrigugal fan blew air under the chassis which escaped via the valve
socket openings thus cooling the valves. There were no valve 'chimneys'

Upon fan failure the pressure switch would initiate the rack's shutdown.

A simple but effective way of cooling the valves.

Frank GM0CSZ / KN6WH