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  • New Supro 1610rt No reverb

    First of all, are schematics available for these yet?

    The reverb tank is a 8EF... type. There’s an AT7 for the drive and half (?)of a the next 12ax7 for the return. Tanks is good, cable checks out ok. There’s lots of high voltage on the AT7 pin 1 376v
    pin2 245
    pin3 250
    pin6 376
    pin7 245
    pin8 249
    changed both tubes
    Do these voltages look good?

    thanks

  • #2
    Voltages don't look good. Might be a missing ground connection. What resistance do you measure between pins 3,8 and ground?
    Do you know the input resistance of your DMM?
    - Own Opinions Only -

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    • #3
      With 245volts on the grids no and 250 on the cathodes is severe.
      Schematic?
      Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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      • #4
        There doesn’t seem to be a connection to ground on pins 3and 8.
        I don’t know the input resistance of my meter. It’s a fluke 175

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        • #5
          Trying to upload a photo.

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          • #6
            Click image for larger version

Name:	image.jpg
Views:	45
Size:	2.86 MB
ID:	910723
            here

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            • #7
              Originally posted by pontiacpete View Post
              There doesn’t seem to be a connection to ground on pins 3and 8.
              I don’t know the input resistance of my meter. It’s a fluke 175
              The tube needs to see a resistance in the k range between cathodes and ground. Find the cathode resistor, check it and verify that one end connects to ground and the other to the cathodes.
              I also suspect that the grid leak resistor has lost its ground connection while still being connected to the lower end of the cathode resistor.
              Especially check for broken copper tracks near the eyelets.

              Does the picture show the cathode resistor? What does it measure? Use your continuity tester to find all components it connects to.

              Input resistance/impedance of the Fluke 175 is 10M for DCV and ACV. Always good to know.
              Last edited by Helmholtz; 08-06-2020, 03:29 PM.
              - Own Opinions Only -

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              • #8
                The open resistor is connected to pi’s 3 and 8.
                I thought it might be 4.7k but that caused one of the dropping resistors I n the power supply to smoke. So I looked up the color codes(should have don’t that first damn metal film resistors) and now I’m using a 47k resistor on those cathodes and the reverb is working. This brought the voltages down about 20-30v on all the pins I gave measurements before.
                Does this sound correct or expected?

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                • #9
                  The resistor in the photo is a 4.7k, I would fit a 4.7k resistor. The type is immaterial as long as it is half watt in power or more.
                  Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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                  • #10
                    Originally posted by Jon Snell View Post
                    The resistor in the photo is a 4.7k, I would fit a 4.7k resistor. The type is immaterial as long as it is half watt in power or more.
                    It's 47k (5-ring code). But its value is unusually large for a rev. driver cathode resistor
                    - Own Opinions Only -

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                    • #11
                      Originally posted by pontiacpete View Post
                      The open resistor is connected to pi’s 3 and 8.
                      I thought it might be 4.7k but that caused one of the dropping resistors I n the power supply to smoke. So I looked up the color codes(should have don’t that first damn metal film resistors) and now I’m using a 47k resistor on those cathodes and the reverb is working. This brought the voltages down about 20-30v on all the pins I gave measurements before.
                      Does this sound correct or expected?
                      Please post all tube pins' voltages.
                      Is the 47k the only cathode resistor, i.e. does it go directly between cathodes and ground?
                      Still wondering what made the grid voltage go so high.
                      - Own Opinions Only -

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                      • #12
                        The 47K is. the cathode resistor to ground for pin 3 and 8.
                        The voltages are
                        Pin 1. 338
                        pin 2. 225
                        pin 3. 225
                        pin 6. 338
                        pin 7. 222
                        pin 8. 222

                        reverb works really well.

                        thanks

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                        • #13
                          Originally posted by pontiacpete View Post
                          The 47K is. the cathode resistor to ground for pin 3 and 8.
                          The voltages are
                          Pin 1. 338
                          pin 2. 225
                          pin 3. 225
                          pin 6. 338
                          pin 7. 222
                          pin 8. 222

                          reverb works really well.

                          thanks
                          Voltage values are still confusing (without a schematic). Incredibly high grid and cathode voltages. As the grid voltage didn't change much, it must be fixed biased.

                          Pin 2 and 7 voltages should be identical and one or two volts lower than pin 3,8 voltages.

                          Does the circuit have a reverb transformer (or do the plates (pins 1,6) connect directly to a supply node)? If not, where does the reverb tank input connect to? Is there a coupling cap that connects to the cathodes?
                          Last edited by Helmholtz; 08-06-2020, 04:32 PM.
                          - Own Opinions Only -

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                          • #14
                            Here’s a picture of the drive it connects to that 200 ohm resistor

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                            • #15
                              Originally posted by pontiacpete View Post
                              Here’s a picture of the drive it connects to that 200 ohm resistor
                              Sorry, I can't work like that. Please answer all of my questions. I can't identify resistor code colors in the picture nor can I read the circuit from a single side only. You have the amp and your meter.

                              I suppose that the amp uses a very uncommon cathode follower circuit to drive the reverb input via a coupling capacitor.
                              - Own Opinions Only -

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