Plate current is not as great a concern as grid current. Excessive grid
current can damage the tubes quickly. The power supply is probably not
capable of supplying enough plate current to damage the tubes as long as
the "excessive" current only lasts for several seconds. When tuning don't
worry too much about the plate current being too high for a few seconds. Be
more careful with the grid current.
DE N6KB
On Tue, Oct 24, 2023 at 6:33 AM Floyd Sense <floydsense@gmail.com> wrote:
> Hi Ted. I have a Centurion now and have had a couple of others in the
> past. First question: how are you measuring the 600 watts? I suggest
> using a constant carrier mode so there's no confusion about peak reading
> or average reading wattmeters. The 6 pots on the display board that are
> used to calibrate the meters are really poor and almost impossible to
> adjust properly when calibrating the meters. I have replaced all 6 pots
> with multi-turn Bourns pots - those are easy to adjust and unlike the
> original pots they will hold the adjustment.
>
> It's always a good idea to adjust the Centurion meter and bar LED power
> readout using an external wattmeter of known accuracy. I use an
> LP-100. The plate current and grid current meter scales should be
> calibrated using the procedure given years ago on this forum. If you
> can't find that, I can send you info and photos. That calibration is
> done with no power to the Centurion.
>
> You won't get any more power out than what you're seeing if driving
> with 25 watts. To get to a KW out requires 50 watts on 160 meters and
> gradually increases to 75 watts on 10 meters. Some use as much as 100
> watts drive. Guess it depends somewhat on the tubes and of course your
> skill in setting the load and tune controls. When you say "excessive
> plate current", exactly what level do you consider to be excessive?
> And, keep in mind that your plate current meter could be far out of
> calibration. The stock adjustment pots will change settings with
> vibration and shock from shipping over the years.
>
> One other thing, adjusting some of the meter pots requires you to remove
> the cabinet. Whatever you do, don't allow the high voltage safety
> interlock lever to contact the HV terminal when there's still HV
> present, even with the Centurion powered off. Doing so will likely
> damage the bias transistors.
>
> 73, Floyd - K8AC
>
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