I bought a used sb200 and I have a problem with very low output. I have good hv shown on the meter both tubes filiments light up. with the amp off rf passes through easily and the built in swr meter works when you turn the amp on the exciter sees swr at infinity, only tried on 40 meters. using the exciters built in automaticd tuner will correct the missmatch. driving with at least 60 watts I get almost no output. tune and load controls do seem to work. plate current is very low and grid current is too low for the meter to read. I have cleaned the tr relay and input band switch that was no help. Can the tubes be so bad that all this happens? I use an external relay to protect the ts2000. I do not have the alc connected. the unit is running on 230vac. there are no known mods to the amp.