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Rickenbacker M-14-A Mysteries

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  • Rickenbacker M-14-A Mysteries

    Hey guys

    Working on a Rickenbacker M-14-A combo which i can find next to no information on. It's a 12" tube combo. 3 x 12AX7s, 2 x 6V6, and a 5Y3. It's got some very low voltages that have me wondering if it's where it should be. The 6V6 tubes are getting 370vdc at the plates, and a whopping 107vdc at the grids. The tubes are cathode biased with a 200 ohm 10 watt resistor that's showing 5vdc at pin 8. The phase inverter is showing 93vdc on pin 1, with 13vdc on the cathode pin 3. The other half has 52vdc on pin 6, and 0vdc on the cathode, which is a 2.2k resistor going to ground. Does anyone have any experience with these?

  • #2
    Which grid is showing 107VDC, the screen grid? If the control grid was at 107V I don't think you would see a low 5V at the cathode.
    Unless you have lost the ground reference for the tube, then your meter is just measuring a floating voltage.
    What is the voltage with one probe at cathode and the other probe at control grid?
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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    • #3
      It was the screen grid showing 107vdc. I combed over the wiring a bit and found that someone had the screen grid wire coming off of the last 40uF cap in the chain (There are four in the circuit). I moved it to where i assume it should be, second in line after the first 40uF which supplies the B+ to the OT. Now i'm seeing 343vdc at the plate and 190vdc at the grid. My cathode is at 10vdc. The amp sounds much better.

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