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  • Ampeg reverbojet J12R

    Hello, everyone,
    I'm back after several months, this time, dealing with an Ampeg reverbojet J12R guitar amp. Among several other problems, the panel meter is burned out. It reads open circuit. I just spent way too much time searching for a replacement. No surprise that the search failed. So, now I am confronted with trying to retrofit some other meter. I will guess is it's a VU meter, thus, likely a 200 microamp meter. Just wondering what my options are. For example, can I pick up an analog panel voltmeter, and remove any resistors, etc attached to it, turning it into a meter that will work on this Ampeg? Any other ideas? I tried dismantling the meter in hopes that I could repair it...no way!

  • #2
    Click image for larger version

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    Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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    • #3
      I don't remember seeing panel meters on them either. But sure enough"
      https://reverb.com/item/27737901-amp...2-guitar-combo

      But if you need to replace a panel meter, look in small print down at the bottom edge of the dial plate. Often it will say "50ua movement" or some such. Sometimes written "20,000 ohms/volt". Or even just 1ma.

      Click image for larger version

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      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Enzo,
        I had to chuckle looking at your photo....mine isn't that bad, but it's control panel is also quite "weathered" as well. Yes, that's the level meter that I am talking about allright! I went to ebay, and found a 200 microamp meter for a very fair price. Not sure it will work, but if not, it was cheap. This panel meter is driven through a series 33k resistor, so I can always modify this resistor...hopefully. So, I'm guessing we want the meter to just enter the red zone at the onset of clipping?

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        • #5
          Why assume the meter accurately represents anything at all? This is just a guitar amp, and the meter is just eye candy.

          Onset of clipping where? Power tubes? Phase inverter? Preamp tube?
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Originally posted by johnhoef View Post
            So, I'm guessing we want the meter to just enter the red zone at the onset of clipping?
            That is what they say in the owners manual, see attached. (page 1, #7)


            Attached Files
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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            • #7
              I probably have something similar here out of a tape recorder, i've got half dozen or so, give me a day to look. Besides full scale current there is also series resistance but you should be able to rig it up.

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              • #8
                Mozz,
                Here are a few photos of the meter. The critical dimensions are the size of the protruding window, as shown by the ruler. 1 3/8 inch wide, and 5/8 in the other direction. Thanks for checking your stock.

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                • #9
                  Old tape players, or look for some old test equipment that might have a similar meter.

                  We had a little old guy at a place I worked in the 80's who was a wiz at fixing those

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                  • #10
                    If you found a flat faced meter that works, I doubt anyone would notice that the plastic didn't stick out into the panel hole.
                    Education is what you're left with after you have forgotten what you have learned.

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                    • #11
                      https://www.ebay.co.uk/itm/1x-Analog...MAAOSwI9le-fqe

                      I have bought stuff from this guy before and it is quality.
                      Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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                      • #12
                        A lot of times (older american made movements) you could unscrew the original faceplate and move it to the new movement. These japanese appear plastic and sealed. These are the ones i found, 2 on the right may work for you but one is stuck full scale.
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                        • #13
                          I've had some success prying open glued-up meters to use my own scale, but make sure your printout is light-fast otherwise it will quickly fade. I found that out the hard way. I did wonder if I could rewind a coil, but I never came across a meter where it would justify the time and patience involved.

                          It's quite amusing that they fitted a meter in the first place - maybe a sales gimmick? It's perhaps as accurate as a fairground grip strength tester.

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                          • #14
                            I agree with others about the meter. It's just a gimmicky thing and you could probably find any meter that fits and then modify the circuit to read something (clipping point?). As to the reverb tank,.. It's been an ongoing battle for Ampeg owners to repair busted reverbs. A brief search turned up this:

                            https://www.amplifiedparts.com/produ...decay-2-spring

                            Don't know for sure if it's a good option. But it's cool that someone stepped up to fill the gap and I've found the MOD tanks to be as good an option as any.
                            "Take two placebos, works twice as well." Enzo

                            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                            "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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                            • #15
                              Originally posted by Mick Bailey View Post
                              It's quite amusing that they fitted a meter in the first place - maybe a sales gimmick? It's perhaps as accurate as a fairground grip strength tester.
                              Ampeg's meter was just a sales gimmick obviously. Japanese top-of-the-line Elk Custom 150 amp had two, wowsers! I have one of those in the rebuild queue right now. And Ashdown must attribute part of their success to mounting a buck-&-a-quarter m.i.c. meter on their amps in more recent years. Back to Ampeg - those copper-plate chassis amps are rare as rocking horse turds. That's not to say they were fantastic amps, hardly, just rare. A short run towards oblivion before Ampeg brought that trend to a halt & returned to making decent amps, without meters or other gimmicks.

                              Enjoy. Every. Sandwich.

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