hi all and thanks for reading this. i have 30-s1 which i purchased about 10
years ago. the amp has been a good workhorse and i worked much dx with it.
recently it devloped a problem where i would lose power out for no reason.
transciever output was normal and a check of the input relay showed no
problems. i substituted a spare tube, but same problem again. i finally
traced the problem to a bad input cable between the input relay and the
input circuit of the amp. the cable had been routed close to the 3 100 watt
hv bleeder resistors and over the years the center conductor had migrated
over to the shield of the coax. well that problem is cured but another
developed. the amp works fine on cw. as soon as switch to ssb and key the
transciver, the plate current goes full scale and trips the plate relay.
this is with no drive. the amp will not idle at 200 ma. i have checked the
bias voltage which is normal. it is almost like the tube is going into
self-oscillation when it gets the higher plate voltage. the spare tube i
put in was a 4cx1500b. i know it needs some different screen and bias
voltages, but i dont feel it should have caused any problems for a test.
both tubes perform ok on cw. any ideas what it could be ?
thanks inb advance.
73, ed
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