>> So now I see a lot of big bang warnings about the SB-230 posted. ......
...snip...
>1.) It has no grid protection circuit, making it possible to easily
>overdrive and damage the grid.
>
Over-drive is most likely to strip the oxide coating from the cathode.
[see photo in "Parasitics Revisited" (9/90 - 10/90 QST) All of the
8873/4/5 grid damage that I have looked at under the microscope has been
due to the gold plating on the grid boiling away. Gold boils at 2966
degrees C. The idea of being able to raise the grid to such an extreme
temperature with over-drive is amusing. ........ Maybe, just maybe,
something else is causing the gold to boil.
>Add a FAST electronic grid overload protection circuit.
>
The majority of gold-boiling episodes I am familiar with reportedly
occurred when the grid current was normal - prior to a Big Bang. .
>2.) It has too low an ESR in the supply line, allowing momentary
>internal arcs to damage the tube.
>
>Add a twenty five ohm 25 watt energy absorbing resistor in the B
>plus lead.
>
good idea. This would limit VHF grid current during an oscillation
condition.
Rich---
R. L. Measures, 805-386-3734, AG6K
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