6g15 build powers up with no reverb

Discussion in 'Amp Tech Center' started by Dsav54, Apr 8, 2020.

  1. Dsav54

    Dsav54 TDPRI Member

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    Hey y'all,

    I finished wiring up my 6g15 reverb unit tonight, went through and tested the b+ which was around 336v. I threw my tubes in and to my surprise, It worked! Well... kind of.. it was hum free and my guitar signal came through clear, except for one issue. The reverb didnt work. Not even a sound when hitting the tank.

    I swapped the rca cables back and forth, and I took my time perfecting my solder joints. Nothing visibly seems out of whack. Now this is my first build, and though I've done a boatload of research I haven't found much on this particular issue.

    Any thoughts?

    -Dave
     
  2. D'tar

    D'tar Friend of Leo's

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    How about some pictures and some voltages for each tube every pin. Good you are passing signal!lets get some verb in there!!!

    Is your pedal plugged in?
     
  3. Dsav54

    Dsav54 TDPRI Member

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    Here's a shot of the inside. I'll post voltages when I get home tonight. Anyone have any info regarding acceptable ranges on these pins?

    Thank you!
     

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  4. sudogeek

    sudogeek Tele-Meister

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    Sounds like only the clean side is working. Try:
    Detach the pedal - may be shorted or not working.
    Check the wiring at the pedal jack.
    Check that the reverb side of V3 (the 12AX7/7025) is wired correctly.
    Check your wiring of the ‘Mix’ and ‘Tone’ pots.
    Switch V3 for a known good one.
    Could be other things like the output transducer in the tank (pretty small fragile wires), bad reverb tank cables, etc. The fact that you get no ‘crash’ when you tap the tank could mean the tank is dead (output transducer broken) or there’s a problem downstream from that point.

    Good luck. Sounds fun.
     
    Last edited: Apr 9, 2020
  5. Dsav54

    Dsav54 TDPRI Member

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    Awesome, I'll definitely check those! Thank you. I'm realizing now after taking a break, that it appears I've got the foot switch and out Jack wires swapped around.. I really hope that's all it is. Updates coming this after noon!
     
  6. Mr Ridesglide

    Mr Ridesglide Friend of Leo's Silver Supporter

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    Some tanks come with a foam damper on the springs so they can't vibrate while shipping.... Don't ask how I know this please :)
     
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  7. Wally

    Wally Telefied Ad Free Member

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  8. Dsav54

    Dsav54 TDPRI Member

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    Okay, so I double checked my connections, swapped both v1 and v2, and re soldered all the pot conn.. and several other checks. I now can hear the tank crash, but still no verb on the guitar. Leads me to believe it an issue prior to the tank. I also tried a different tank and its the same. Not really sure what to try at this point.
     
  9. sudogeek

    sudogeek Tele-Meister

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    Keep working backwards.

    Is the tank connected properly? The tanks commonly used in Fender tube reverbs and clones are 4AB3C1B (for more than you want to know on that, see below*). The first ‘C’ denotes that the input jack of the tank is insulated and the output jack is grounded. You can tell which is correct just by looking at the jack and seeing which one has an insulating washer. This is generally on the left (with the open side on the tank facing away from you). That one should be connected to the (reverb send) cable coming off the reverb ‘input’ or send jack connected to the reverb transformer secondary leads. If you have the tank input and output cables switched, you’ll still hear the crash when you hit the tank but your reverb will be faint or absent.

    Also, see the above comment about the foam pad. In addition, do you have one installed as a spring damper for transport? Are the springs moving freely?

    [*By the way, which reverb tank are you using? The proper tank for the 6G15 should be a 4AB3C1C (the final C demotes vertical mount, jacks up). In fact, many (all?) vintage Fender tube reverbs I have opened up actually shipped with a 4AB3C1B (B denotes horizontal mount). This is the same tank Fender used in their reverb combo amps, mounted horizontally in those amps as is correct for the B tank - just another example of Fender’s cost-cutting I guess. If you look at kits being sold today, Mojo, Triode, and others also go with the ‘vintage correct’ 4AB3C1B even though it’s not exactly the proper tank for mounting vertically on the front of the cabinet. I’ve played around with this and the 4AB3C1B works fine but, imo, the 4AB3C1C tank has a bit longer decay as compared to a 4AB3C1B even tough both are nominally long decay. /pedantic]

    If the tank is connected correctly, next, check your wiring of the reverb transformer and the reverb out jack. Then check your wiring on the 6V6/6K6. The picture isn’t too clear. Are the blue and red wires soldered to the same pin? Some other views may be helpful. Keep at it; you’ll find the problem.
     
    Last edited: Apr 9, 2020
  10. Dsav54

    Dsav54 TDPRI Member

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    I've got the mod 4ab3c1b. The foam was removed apon installation. I'm redoing more connections including those from the transformer. The connections all seem great, I cant imagine where this problem is coming from. I appreciate the help! :)
     
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  11. Mr Ridesglide

    Mr Ridesglide Friend of Leo's Silver Supporter

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    You are close now
     
  12. Dsav54

    Dsav54 TDPRI Member

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    I'm wondering if it has anything to do with the transformer/s
     
  13. StevenPituch

    StevenPituch TDPRI Member

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    This might help. If the tank is a 4AB3C1C, then it’s input is 8 ohms. In that case you could plug your speaker to the reverb input jack on the amp and you should hear a clear guitar tone through the first reverb tube.
     
  14. D'tar

    D'tar Friend of Leo's

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    Voltages sure would be nice. They may hint to what the issue is or what it is not!
     
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  15. Dsav54

    Dsav54 TDPRI Member

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    Ok! I've got voltages for y'all.

    6k6
    Pin 1/8. 23v
    Pin 3. 277v
    Pin 4. 286v
    Pin 5 276v

    V2
    1 64v
    2 0v
    3. 2v
    6 224v
    7. 101v
    8 117v


    V1
    1. 62v
    2. 0v
    3. 1v
    6 66v
    7 0v
    8 0v.

    Filaments were at 5.9v AC

    So it sure does seem like v1 has something going on. But what would cause that?

    Also, this is the exact layout I used for this.
    https://el34world.com/Hoffman/files/Hoffman_6G15.pdf
     
    Last edited: Apr 9, 2020
  16. Snfoilhat

    Snfoilhat Tele-Afflicted

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    V3 6K6 pin 5 is the control grid. It should read 0 VDC.

    V1 12AT7 pin 8. A reading of 0 VDC indicates the cathode is shorted to ground (or no current is passing through that triode--which is also possible but doesn't fit with the power supply being sagged down). Recheck that 1.5 k resistor.
     
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  17. Dsav54

    Dsav54 TDPRI Member

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    Resistor reads 1.5k and has continuity on the side opposite of the tubes to chassis. I just double checked pin 8 and it is at 2v now.
     
  18. sudogeek

    sudogeek Tele-Meister

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    The voltages on V2B are too low. This is 1/2 of the 12AX7/7025 which acts as the recovery stage for the reverb channel. The plate voltage (pin 7) should be similar to V2A and, for a 12AX7, in the 120-180V range. The plate voltages on both sides of V1 (the 12AT7) are also too low.

    What are the voltages at the + poles of the 40uF filter caps (points A, B, and C on the Hoffman schematic)?
     
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  19. Dsav54

    Dsav54 TDPRI Member

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    A is 296v
    B is 290v
    C is 230v

    I also noticed the filter caps drain completely within 3 seconds of powering off, not sure if this has something to do with a short to ground or a built in feature.
     
  20. D'tar

    D'tar Friend of Leo's

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    Your voltages reflect some issues. I Would recommend going over the circuit with a fresh copy of your layout, your meter and a highlighter. Verify each component, every wire, every connection. Pay close attention to the areas on the board where components cross over ground and power bus. Some component leads look awful close to making unwanted contact with other components.

    A few more detailed pictures with shots of the tube sockets back of the pots and the board will help spot issues.
     
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