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. 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".
The cabinet is well ventilated with a 4" inches muffin fan blowing air
at 3/4" into the tube and another fan on top of the cabinet (which is
perf aluminum sheet), helping the air out
I use two 10v 50W zeners in series for CW and short one for SSB;
Plate : ~ 3500VDC no load to 2800VDC full load
Ip full load : ~ 300 to 370 mA depending on band
Ip idling : 35mA CW - 70mA SSB
Ig : ~ 80 to 110mA depending on band
Fil, volts : 4.8VAC . Since I use a separated transformer for fil,. and
plate and also a different wall outlet, I assume that it stays around
this value with or without load.
I had some bangs and arcs before but changing the parasitic supressor to
one of Measures designs seems to have solved the problem.
Shall I expect a shorter life from this tube ?
What is the "proper" color for the plate under the mentioned load
circumstances ?
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 ?
Thank You!
73 de
Hugo Catta
CX9AAK/W2
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