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I am restoring a 37-620 Philco and need advice regarding the cathode circuit of the 6A8 tube in the RF chassis. I purchased a set of service bulletins and schematics from Chuck and in reviewing the schematics, the earlier version bulletin #250 shows the cathode of the 6A8 connected to chassis ground. My 37-620 seems to be a second run with some updates but has the cathode grounded. A later service bulletin #251A has a 100 ohm, #21 and a .05 cap, #19 to ground. Should I install the later version or leave the grounded cathode? Many thanks for your help.