I recently purchased a 600A. I have the manual, parts list and schematic. I am having problems getting good DC voltages and AC voltages for the plate supply circuit using Daniel Schoo's Calibration recommendations that are posted on the Hickok site.

I have replaced the 83 mercury vapor tube and the 5Y3 tube from Antique Electronic Supply. I notice that a 25z5 tube will test good, while a known good 75 and 78 will test bad. I have tested the resistors and they appear within spec.'s I have noticed that tubes that use a grip cap connection, seem to test bad. The grid cap cable itself test o.k.

I need suggestions of points to check to help troubleshoot the problem. Any help would be greatly appreciated. We have a great group here, thanks everyone.

Kevin

Can you generalize that rectifiers test good, but tubes with control grids don't? How about triodes vs. pentodes? Or do the problem tubes always use the same switch number settings? The grid cap has its own switch position, doesn't it? Maybe the switch needs cleaning: that position may never have been used by the former owner.