Hello, all. I am new to this community, and I hope someone can help me. I have recently purchased a Hickok 605, which turned out to have a few problems. Even though it tests rectifier tubes such as 5y3, 5z4, and 5ar4 correctly, it does not function properly when I attempt to test 6v6s and 12ax7s. Both 6v6s and 12ax7s are tested with the use of the p4 switch, while the aforementioned rectifiers use the p3 switch. It appears that nothing happens (the needle stays still) when tubes that require the pressing of the tester's p4 switch are tried.
Can anyone please instruct me as to what may be the problem with this tester? I am thinking, first, of replacing caps and resistors, but since I do not have the schematic for this particular tester, I cannot be sure of the correct values. If anyone knows where to locate the schematic for the Hickok 605, kindly let me know. In fact, any help/advice would be appreciated.
Thank you so much in advance.