[Heathkit] SB-220

[pacho]

Hi all: I need help with my SB-220. The problem is as follow:When the
amp is turned on the plate voltage is 2570 V, and the standing current
is 200MA (it seems high).
After tunningn, output in CW is 500 watts, with 500MA and the grid 175
MA. Opertion seems to be good, but after 5, 10 minutes  or longer of
operation the current in plata increases above 600 Ma and the output of
the amplifier drops to 20 watt or les.
The tubes were replaced about a year ago and have not operated for
manyhours.    they were replaced because one of the tubes was not on .
Upon removing, one was found to have the filamente open.Made o hole to
make a lamp. Latter found in the net that most of the times the solder
wouldflow out indicating  an open filament. IGNORANCE OF ME! Could the
problem be in one of the sockets of one of the tubes?help and comments
will be greatly appreciated.
Thanking in advance,
Frank/WB4EHB .