In a message dated 7/20/2005 3:13:43 A.M. Central Standard Time,
craxd@engineer.com writes:
Dick,
I'm not saying it's a bad tube, and dont want none to think that. I just
dont want anyone to undercool the tube so it will last. Who knows, the 4CX1500
may have an over-sized radiator too! About the only way to tell about the temp
would be to use a thermocouple connected to the anode. Then the temp read
under contesting conditions both under SSB and AM using the air flow they
recommend. AM/CW creates a good bit more load on one as does SSB
transmissions.
Then if the temp stays down where it should, one would know it would be ok.
I'm
like Rich, and what George mentioned, use the largest blower possible.
Another thing too is maybe mount and external blower and duct it to the amp.
You
can set one of these in another room to help kill the sound down if it's a
concern. On yours, you may have the right combination by using enough fans
both
pushing and pulling. Have you measured what the air flow and pressure is on
your amp? If so, let us know so we all have a starting point.
Best,
Will
GU84B data at the ND2X website shows 57 cu ft per minute air flow at 1.2"
back pressure. There are Dayton blowers readily available from Grainger Supply
that will do this.
Running the tube at 3000v, 1.7A , class AB1, locked key, would generate a
heat load of about 1900 watts.
Using the heat rise equation from the ARRL Microwave/UHF Experiments manual,
room temperature into the tube would exit at about 190 degrees F (88 degrees
C).
This sounds like a reasonable scenario doesn't it? AM linear operation will
back the dissipation way down as would cw or ssb.
Doesn't seem even that multiple blowers would be neeeded.
73,
Gerald K5GW
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