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Ampeg Gemini II G-15 quirks

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  • #16
    just posting to be included on future posts

    Cool stuff guys! I have been working on three different Ampegs (Jet, Reverbrocket, B-12XT) lately and like to stay up on what other guys are doing with their amps...

    keep going on this, and I do hope you post more pictures

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    • #17
      An update on the G-15

      Just a little update about the Gemini II:

      -- Cord replaced, death-cap removed.
      -- Removed the modified channel-routing.
      -- Most of the filter caps replaced, the can cap is on order. The amp is, and always has been, very quiet. But it's just routine maintenance for an older amp..
      -- Replaced the 7591's.
      -- Found a vintage Heppner 15" Alnico speaker. I know opinions vary on these, but, wow, what an improvement... (well, that and the power tubes.)

      There are still quirks to case down. There is still some reverb on the second channel. Maybe 1/4 of the amount on the first chan. Maybe that's normal, I don't know. The channels don't sound identical, even with the reverb an trem off...

      But the amp has been transformed from sounding "dead thud" to bright and very much alive. With the treble past 3 oclock and the volume above 2/3rds, it odrives nicely. Sure, it's not a Bassman, but anyone who says the G-15 is "clean only" needs to change the 7591s...
      Attached Files

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      • #18
        One more update...

        Finally chased down one remaining issue with the Gemini II today--one of my own making.

        I'd done some mods of the incoming mains wiring, including the usual three-prong plug, ditching the death-cap, etc. In the process I added four 5W 12V zeners on the PT secondary centertap to drop the voltage a bit closer to 1965-66 levels...

        Being too clever for my own good, I modified the standby/polarity switch to for a choice of either the low or the full voltage (no zeners.) The mod words well, but the lower voltage is always noiser...especially on channel one, which also needs to be zeroed when using channel two.

        However, the Gemini has an unusual (to me) way of wiring the power lamp that works in conjunction with the standby. I just discovered that the lamp, etc., was wired such that in the low voltage setting it was on the PT side of the zeners, and therefore elevated at that setting... sigh.

        Sorted it out by using the unused side (formally death-cap) of the standby/polarity switch for the pilot lamp. It's now super quiet--I can even jumper the two channels together without noise for the first time...

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