<color><param>0100,0100,0100</param>Hi Scott,
<italic><color><param>0000,0000,0000</param>> These tubes have white ceramic
bottoms with no external markings
> on them except for a "P" on the glass. There is some handwritten
> marking on the inside of the tube, but just numbers. Do these
> sound like the Svetlana 811a or some Chinese clone?
</italic></color>They are "Russian" tubes, for whatever that is worth.
<italic><color><param>0000,0000,0000</param>> Without having the extended
experience with 811a tubes as many
> of you do (it's only my 3rd amp), what would cause the plates to
> curl like this-just excessive heat, improper loading, improper
> cooling?
</italic></color>Too much anode dissipation. It has nothing to do with airflow,
since
that is an INTERNAL anode tube and the air never hits the anode.
The continuous anode dissipation is 65 watts, although the tubes
will take higher amounts for short periods. The 65 watt rating is for
natural convection without forced air, or with 1000 CFM of air,
whatever you like to use. The only thing air does is prevent the
OUTSIDE of the tube from melting.
<italic><color><param>0000,0000,0000</param>> One of the things that I looked
at on the 811h amp when I saw this
> was that it only has one area for air outflow, and it looks to favor the
> capacitors in the power supply. The tubes really don't see all that much
> air around them. On my sb200 (2) I had always put a muffin fan on top of
> the amp to pull the hot air out and keep the internal temperature down in
> contests. What's the general consensus on installing a screened vent over
> the rf section to vent air there?
</italic></color>Leave it alone. If you do a air flow test or temperature test,
you'll
find every runs within ratings as long as you follow the manual.
Unlike poor designs that blow air on the hot tubes and then
circulate that hot air all over the components that can't take heat,
this design blows air across the coolest parts that can't stand any
heat first and hottest parts last just before the air leaves the
cabinet.
If you blow air across the tubes first, and then let that air hit the
electrolytics you'll have to greatly increase airflow or you will ruin
the electrolytics.
<nofill>
73, Tom W8JI
w8ji@contesting.com
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