Hi Jim et all
> I have a weak memory that people used to put another
> tube instead of the 4CX1000 in the 30-S1, can someone
> refresh my memory.
4CX1500B...has same screen dissipation (12W) but LESS
(nominally zero W) grid dissipation. In many ways the 1000A
is a better tube than the 1500B - you get just as much RF out
with the 1000A
> How much power can then a 30S-1 put out, original and/or
> modified.
I don't have a 30S-1, but spent time repairing one belonging to
GM4AFF. The un-modified 30S-1 is good for about 1000 W
O/P but gets very hot at this power level in e.g. contest use.
There are several problems about getting 1500W output from
a 30S-1 :-
1. Poor cooling - the blower has too low a flow rate, and the power
supply has no forced-air cooling. I fitted an extra fan blowing cold air
in at the base of the PSU. It looks very difficult to replace the
existing blower with one with a larger flow rate - one (drastic)
solution would be to mount a large blower on the side of the RF
deck and pressurise the whole plate compartment.
2. The plate voltage is too low - however a higher voltage xfmr
cannot be installed without changing the (paper) HV smoothing
caps. 4CX1000A/1500Bs need about 3200 V on the plate.
3. The plate blocking capacitor looks very small - maybe marginal
at 1500W ?
4. Screen supply mods. as discussed, to give +325V DC regulated
at + and - screen current.
Despite all these comments, the 30S-1 is a great amp - it's got real
'presence' in any shack !
73
Chris GM3WOJ
www.qsl.net/gm3woj/
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