Home Forums Electronics Restoration Finally, tube substitution saved the day!

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    johngillespie
    CVRS Member

    Many years ago, I purchased a Hewlett Packard 606A (Very heavy) signal generator on (the bay) as not working or for parts from a person in Oregon for $40. It had been used by Alaska Airlines. The beast was shipped across the continent to Ontario for $80. It was very poorly boxed in a thin cardboard box with no protection whatever, except a thin piece of Styrofoam to protect the front knobs and meter. It arrived undamaged, probably because of the heavy metal case. Weight may have saved it, it couldn’t be tossed! The box had busted open at the seams and the Styrofoam fell out. So far so good, at least it arrived in one piece.

    I removed the case and powered it up. Sure enough, it was DOA (dead-on-arrival) as advertised. So, there on the bench was my new signal generator for the princely sum of $120. not bad! Simply removing the tubes and testing them broke any oxidation that may have existed in the tube sockets and tube pins and after testing, the beast came alive! It was, and always has been, my go-to signal generator. I have never serviced it, replaced any caps or resistors etc. The beast works like a champ, is dead on frequency every time I need it.

    Then…. one day after maybe 10 years it let out some smoke! Yikes, what happened? I pulled it from the rack, removed the cabinet and started hunting for the problem. Everything seemed like new in there! Every circuit I checked with schematics and manual in hand looked perfect. There were two resistors getting hot, but for the life of me I couldn’t explain why. I checked the tubes, all the circuitry… everything, and nothing appeared out of the ordinary except those two hot resistors. In frustration, I put it back on the shelf and gave up, other things were pending.

    Finally, one day, I needed my generator and had to source the problem once and for all. Again, I rechecked everything and again there was simply no explanation at all! Finally, I sat down with the manual and started reading. I should have done this from the beginning. There in BOLD LETTERS it read…. “if you are experiencing problems, Start with tube substitutions”. That’s not something I usually do. I subbed the tube in the problem circuit with the two extra warm resistors and sure enough, the beast came alive! Wow, it was a bad tube all the time… even though that bad tube tested perfect in my tube tester!

    Tube substitution… who would have thunk it! John

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