I've run my 30S-1 at a higher screen voltage for years and highly recommend
it. With the higher screen voltage, the amp easily runs 1500W output (it was
designed for 1000W input, to be consistent with the prevailing US legal
limit at the time). Further, it is much harder to abuse the screen current
rating of the 4cx1000A, when its running at a higher screen voltage. I ran
extensive before-and-after tests when I made the modification, and can
probably find my notes if anybody is interested.
There are two common ways to implement the screen voltage modification. One
is to swap the plate transformer for a Peter Dahl replacement transformer,
which provides about 100V higher screen voltage. (This is what I did with
my 30S1, because the HV leads on the original xfmr were cracked and worn
where they exited the body of the transformer.)
The second, much less expensive route, is to use an ordinary 100W (or more)
isolation transformer that sits on the accessory shelf of the 30S1 power
supply enclosure. The primary of the transformer is wired to 120VAC and the
secondary is in series with the plate transformer screen voltage tap. This
is a ten minute modification.
As I recall, there's also a 350V electrolytic filter capacitor in the screen
power supply that many users swap for a 450V unit. Doing so is optional, but
a good idea, since the original capacitor is probably somewhat iffy after
all these years.
73,
Jim W8ZR
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