> As someone stated, remove that cap and you will find a pinched-off tube which
> was used during creation of a vccuum in the tube. The tube just looks nicer
> with the cap. (the plate cap has nothing to do with the cooling of an 8877).
> Check out the EIMAC Y-503, 8755, 8767, 8847A, ML8538/8933/8538B,Y-540, Y-654
> for examples of the pich-off tube process (thas just a few of the TETRODES).
> If you really want a plate/anode cooling fin look at the 3X600/Y-872.
Just to emphasise a point here - the cap that covers the pinchoff
is thin metal, with barely any contact onto the rest of the anode
metalwork. The heatflow into/through it is negligible. It
certainly does not get hotter than the rest of the anode.
The add on radiator has horizontal grooves - even if there was any
heatflow through the cap these would not do much in a vertical
airflow. The cooler will be less ineffective if it's solid.
Even if such a cooler was used in a horizontal airflow, I doubt
those grooves would do anything useful. They are too narrow. Air
will go round, not through them unless it's very high pressure and
applied from a narrow jet very close by.
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