Tom.
TT Centurion has two 3-500Z. The red LED in that amp is for power > 1250W.
The flashover was a few minutes after turned on when idle.
Ignacy
On 10/1/07, Tom Rauch <w8ji@contesting.com> wrote:
> Ignacio,
>
> One problem with the TT amp is they have no positive
> protection for excessive grid current.
>
> A set of 3CX800's can be ruined in just seconds of operation
> with excessive grid dissipation. Worse yet, the damage can
> slowly accumulate over years of minor or very short
> overloads. The overload LED warning light is really too
> little much too late.
>
> The failure mechanism is the gold from the grids migrates to
> other areas of the tube. This happens from the kenitic
> energy of the electrons hitting the grid, it is an
> evaporation process without the necessity of the entire grid
> overheating.
>
> At this moment I have three TT amps here all with bad
> 3CX800's, and the failure in all three is the tubes arc. The
> tubes only HV test to 2-3kV average and have very low
> emission, and that is a clear sign of severe gold migration.
>
> If it was my amp, I'd put some type of very fast electronic
> overload cutout in it. That would be number one mod.
>
> 73 Tom
>
>
>
>
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