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?

Doug N4IJ

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

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?

Doug N4IJ


I built a linear using two 4-400's. I used the Johnson ceramic
sockets (square type) that did have some holes which lined up
with the ones in the bottom of the tubes. I mounted the sockets
under the chassis FLUSH with the bottom of the chassis. I pressurized
the chassis with a 4" boxer type fan mounted under the tube sockets.
This fan was one of the high speed types that could move lots of air.
I also mounted a pair of the same type of fans next to the
bottles on the top of the chassis, blowing air from outside
into the chassis past the tubes. The air flow went through the base holes
and around the glass bottle. This is similar to the way the
SB220 linear was build, as with many HB amps. The tubes did not
suffer any heat effects, while the pair ran near the legal limit.

BTW, 4-400's work ok in GG, but they like more HV than their triode
counterparts. While a pair of 3-500's work well with 2500v, the 4-400
likes more like 3300-3500v to get the same output and IM figures.
So your tank circuit will have more "L" and less "C".

On Sun, 5 Mar 2006, 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?

My recollection from Eimac tube spec sheets is that there must be
forced-air directed upwards from the non-tube side of the tube socket and
there are specifications for flow rate and pressure. Both the 3-500 and
4-400 (100 watts less plate dissipation) call for 5 v at 15 amps (IIRC) on
the filament and that is a lot of heat. I don't know if the 3-500 is
pushed closer to the limits on this but Eimac made a special socket (and
chimney) for the 4-400 but many ARRL handbook amplifiers went for a much
simpler socket. And, the Johnson Thunderbolt (I had two of them at one
time) used a simple ceramic socket plus an under-chassis phonograph motor
type of fan to blow air up from the bottom as well as an above chassis fan
motor to blow more air around the pair of 4-400s for a 1 KW DC plate input
level (with dull red cherry glow on cw carrier and a little less glow on
SSB voice).

Beyond that, if you are thinking of running 4-400s instead of the 3-500z,
you also need to worry about bias voltage a little and you would have to
resolder the socket pins because the 3-500 is a triode and the 4-400 is a
tetrode (need to ground the screen, as well as control grid). But I have
run 4-400s in GG in a homebrew amp in the past.

Doug N4IJ

ORIGINAL MESSAGE:

Straydog wrote:

there must be forced-air directed upwards from the non-tube side of
the tube socket and there are specifications for flow rate and
pressure.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Flow rate and pressure" are nice, but the *only* important thing is
the temperature of the tube at various points as specified by the tube
manufacturer. If you are serious about proper tube cooling, use either
a non-contact thermometer of some kind or thermally-sensitive paint to
ensure your tube is within temp specs. Flow rate and pressure are a
means to an end, not an end in themselves.

Bill, W6WRT

Why is the dissipation rating of the 4-400A lower when used in grounded grid
service than it is when used in the traditional configuration?

73,
Bob AD3K

"Bill Turner" wrote in message
...
ORIGINAL MESSAGE:

Straydog wrote:

there must be forced-air directed upwards from the non-tube side of
the tube socket and there are specifications for flow rate and
pressure.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Flow rate and pressure" are nice, but the *only* important thing is
the temperature of the tube at various points as specified by the tube
manufacturer. If you are serious about proper tube cooling, use either
a non-contact thermometer of some kind or thermally-sensitive paint to
ensure your tube is within temp specs. Flow rate and pressure are a
means to an end, not an end in themselves.

Bill, W6WRT