>Hi, All!
>
>My homebrew amplifier has a 3-500Z with a clearer color spot in the
>middle of the plate visible through the fins that seems to be brighter
>than the rest of the plate surface when loaded.
It may be that this tube has a slight bend in its filament helix. My
guess is the that if this is so, the bend aligns with the brighter spot
on the anode cooler. If you have a high-pot. tester, it might be
interesting to limit the current to 1mA or less and measure the
grid/filament breakdown potential. In a darkened room you might be able
to spot the bend in the filament by looking up through the bottom of the
fins. This is the method we use to determine how to position a tube in
our centrifuge before attempting to straighten the filament helix.
>The tube seems to work
>fine, delivering full power but the plate goes slowly all the way to
>orange after a rather long (two or three minutes), transmission on CW or
>SSB. It is more evident in higher bands. However It does not
>"de-tunes".
... ... ...
>What is the "proper" color for the plate under the mentioned load
>circumstances ?
Orange to orange-yellow colour is normal for a 3-500Z.
>Is the filament voltage "just in the threshold" ?
>Could a drop of another couple of tenths of a volt be damaging for the
>filament ?
>Am I worrying for nothing ?
A thoriated tungsten filament can not be damaged by operation below the
recommended filament voltage.
cheers, Hugo
Rich...
R. L. Measures, 805-386-3734, AG6K
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