Phil,
If you do anything with cooling on the Centurion, in my opinion, the
best way to go is to change the internal fan. I am in the process of
making several changes to my Centurion to equip it for AM at 300 watts
so I have been down this path.
The stock fan is a Bi-Sonic AC fan that runs off one side of the plate
transformer primary and a center tap. It has a metal impeller and is
spec'd at 80 CFM. It is indeed quiet and the cooling is probably okay
for SSB and CW.
If you have had the cover off you know the tubes are elevated on a
socket platform that also holds the HV plate choke. The fan sits just
to the left (when looking from the front panel) drawing air in across
the B+ transformer and blowing it out across the RF deck. Part of the
lower arc of the fan extends below the tube platform to blow air to
the pins. What many may not know unless they have had the RF deck
out is that the cathode choke sits down there right in front of the
fan almost entirely blocking the air to the pins. I did not like
that and wanted to move it out of the way but I asked Ten Tec about it
first and was told that lengthening the wires to the pins from the
choke would put on too much v drop to the cathodes. This sounded
plausible so I left it because the space is really tight and there
isn't anywhere else to put it under there. (Side note: I sure wish
amp manufacturers would get over this crazy mania for jamming
everything into as small a box as possible. Those old Alphas and
Henrys got it right.) But this means more fan action certainly can't
hurt as there is some air movement, just not as much as there would be
if the choke weren't right in front of the fan.
Fortunately the fan is a standard size so there are plenty of
replacement fans out there that have higher air flow. For AC, they go
up to 120 CFM as I recall. Beyond that and due to the size limit of
the fan, you have to go with DC. I did that and put in a 180 CFM 12
v. 2 A fan powered from an external supply. For you, that might be
way too much but a DC fan can always be stepped down. Noise? Oh
yeah, it sounds like a vacuum cleaner but that's a trade off I'll
accept. I also opened up the cabinet more. You might find a 120 CFM
AC fan adequate.
You have to take off the cover, remove the tubes, loosen and lift up
the RF deck and remove the bottom panel trap door to get at all four
hex screws on the fan. You need a 9/64 long shaft allen driver. a
telescoping magnet tool helps handle the screws on the bottom holes.
You'll also have to remove the strap to the tank circuit tune cap and
the cathode supply leads. It sounds harder than it is, but I'd do
this if I were to do anything to the cooling at all. If it weren't
for the cathode choke location you might be okay with a fan on the
outside of the RF deck pulling air out since the cabinet is not
pressurized.
73
rob / k5uj
>I have a Ten Tec Centurion that is under a shelf with 3 inches of head room.
>Would I be well served to put a Rotron fan on the tube vents and pull the
>air out for better circulation? Please!
>Phil
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