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Salvaging valuable tubes - (see "dead" tube post also)

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  • Salvaging valuable tubes - (see "dead" tube post also)

    Howdy folks,

    Well winter is always tight for me and since I don't play bass I decided to sell the 1969 Ampeg B-15N that I restored a couple of years ago. I used great quality Sylvania 6L6GC - 387STR outputs that I "pulled" from a Peavey Deuce - the owner wanted new tubes despite my protests, partially because two of them had the locating key broken off.

    But when I fired the amp up recently the output tubes were dead (see companion post). Hmmm, well I did have the other two STRs so I pried the metal locking tabs off the bases of a couple of rusty metal OZ4s that I'll never use (these are really interesting inside but you have to unsolder pin 1 which is connected to the shell to get the base off easily). After unsoldering the other "guts" I used a drill to chew off the tops of the pins and after "thinning" the base a little I slipped it over the STRs with the broken keys. Now just to make sure that I had good pin contact I both retensioned the socket contacts on the tight side and slightly thickened the STR pins with a thin coat of solder. At first I was afraid that I might need to add some sort of retainer as the tubes are upside when the top is "flipped" but the STRs were gripped more tightly than the 6SL7 preamps tubes.

    Just a little tip for restoring those Type I Mullard EL34s with the broken key that you're afraid to plug in.

    Rob

  • #2
    Rob,

    The only time I've seen this type of thing is with two STR387 6L6GC's I accidentally left on standby for 3 days - shiny getters, normal voltages, zero cathode current. You've tried the dead tubes in another amp to be sure?

    I just used those broken-pin restorers Antique sells on two KT77's (their bases are made from some super-brittle brown plastic), and they worked great once I removed every last trace of the original center post so they sat flat against the tube base.

    I've never tried reviving tubes with a higher-than-normal heater voltage, but I've seen half-heater-voltage operation gradually reduce emission, which then pretty much returned to normal when full heater voltage was restored. Hey, there's nothing to lose - and any successful tube-restoration technique's gotta be great news for somebody out there!

    The Tomer book recommends two techniques:

    1) Permanently increase heater voltage 10%, or

    2) Raise heater voltage 50% for a few minutes, while drawing twice rated cathode current. This is basically a "kill or cure", but he says successful results are usually stable for quite some time.

    Ray

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    • #3
      Hey Ray,

      I'm going to attempt the "kill or cure" method when I can get to it - if not I'll add the internals to my collection of tube guts - maybe I'll start a "valve intestinal" museum some day.

      Rob

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