Rivera hundred duo twelve dead V1 tube

Discussion in 'Amp Tech Center' started by Jaymann, Jun 25, 2019.

  1. Jaymann

    Jaymann TDPRI Member

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    I have a Rivera Hundred Duo Twelve and it is having an issue and I was hoping for some help.
    It got really weak sounding and low on volume. I noticed V1 is not lighting up at all. I swapped it with a known good tube and it didn't help.
    I plugged into the effects return from the send of another amp and it's nice and loud.
    Any advice on where to look next?
     
  2. Wally

    Wally Telefied Ad Free Member

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    Your experiment with the effects loop indicates that the problem is in the preamp, so that is a clue. I have to think that V1 is being heated or there would be no signal at all. Have you subbed a known good tube into V2 and V3? If you get no cure with that, it is tech time. That is not the simplest of amps but is well worth getting it up and running whatever it takes.
     
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  3. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

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    I have a Rivera S120-210 which is similar. If Wally's suggestions don't help, get it to a tech and a good one who understands Rivera amps. They are not simple circuits with lots of switches and pull pots and all. But when it's working right, it's a thing of beauty.

    Paul Rivera said that he was building one of those 100 Duo 12's for Jerry Garcia when he died. It was going to have two JBL E-120's in it. Can you imagine what that would have weighed?
     
  4. Jaymann

    Jaymann TDPRI Member

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    I looked closed in a dark room and v1 is dead and v2 is only half lit up.
    I swapped several good tubes in and nothing.
    I started chasing down the problem by following the schematic. There's power all the way to the +18v IC but nothing coming out of it. I'm guessing that's the issue. The -18v IC has power out of it.
    Also while testing one of the filter caps blew. I guess I'll replace them all. The amp is from 1993 so that's long enough for those caps.
     
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  5. Jaymann

    Jaymann TDPRI Member

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    Well, I replaced the ic voltage regulator and the tubes all lit up...for a little while. Now they're dark again and the ic is only putting out about 8VDC instead of 18VDC
    I checked voltage going in and it's around 28VDC. According to the schematic it should be 24VDC coming from a bridge rectifier feeding the voltage regulator. The -18VDC side of the heaters are also getting 28VDC from the bridge rectifier but it is putting out the correct -18VDC
    This thing is driving me nuts!
     
  6. Wally

    Wally Telefied Ad Free Member

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    Paul Rivera has always been helpful if you don’t find the problem. FWIW, he is usually the one who answers the phone.
    It would be good to have a more readable schematic than the one I find in two places online. It would seem to me that one would have to suspect another component in that particular circuit that is taking out that IC. Are the tubes that are being heated with this DC circuit known to be good? Diodes? Caps?
     
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  7. Jaymann

    Jaymann TDPRI Member

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    I found a really good schematic that you can actually read. Took a lot of googling!
    Tubes are good. All electrolytics have been replaced.
     

    Attached Files:

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  8. Wally

    Wally Telefied Ad Free Member

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    JayMann, I would be on new ground here, too. I would start by carefully and systematically testing voltages at all of those test points in that circuit. I would be making a voltage chart so as to assure that I did not get confused. Ymmv...but in your posts you have given us all of this info in a manner that I for one can grasp.
    Something in that circuit...from the rectifier diodes to the tubes...is causing a problem. It is possible that a certain test point will give a clue as to where things are breaking down. I don’t know if a current limiter would help with this type of diagnosis, but I would have mine hooked up to see if it would maintain the circuit long enough to find a problem.
    Did the IC go down again? what IC failed and was replaced?
     
  9. Jaymann

    Jaymann TDPRI Member

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    The original ic was putting out only a couple volts. 28V was going into it. The schematic says it should be getting 24V and putting out 18V.
    It was ic1 on the schematic. A 7818CT
    I replaced it and the test point on the schematic that says 18VDC was right on. The out of the ic also read 18VDC. The tubes lit up and I was happy. I shut it off and came back to it later. When I powered it up the next time, the tubes were dead again and the test point and ic out were only reading about 8v
    IC2 is reading the correct -18VDC
     
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  10. Wally

    Wally Telefied Ad Free Member

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    Are the two test points tp43 and TP45 reading the same?
     
  11. Jaymann

    Jaymann TDPRI Member

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    TP43 8.2 VDC
    TP45 18.1VDC
     
  12. Wally

    Wally Telefied Ad Free Member

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    In that case, I would be looking very hard at D7, D8, and C13. One could assume that Ic1 is blown again. When you replaced that IC, you replaced a component that was taken out by a failure somewhere else in this circuit. If you don’t find a bad cap and/or diode in that immediate area, then you might think that there is a problem on down the line that this voltage source supplies. If you find a bad cap and or diode, replace that and IC1. Before firing the amp up again, disconnect that connection that feeds the circuit through G6/GG6. See if the +/-18vdc circuit holds up when that connection is disconnected. If so, one might think that somewhere in the circuit where that voltage is put to use there is a problem that is taking that IC out. It could be as simple as a shorted heater filament in one of those preamp tubes.
    If the circuit fails even when disconnected from the ‘voltage use’ points, then one starts suspecting any cap and any diode fro: the transformer leads on.
     
  13. Jaymann

    Jaymann TDPRI Member

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    Great advice. thank you Wally. I'll try that once I get back from my gigs the next few days.
     
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  14. Jaymann

    Jaymann TDPRI Member

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    Looks like it was the Bridge rectifier that comes before IC1. I replaced that and the IC and I'm getting a steady 18v now.
    Thanks for the help Wally.
    Just need to bias this and it's good to go.
     
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  15. Wally

    Wally Telefied Ad Free Member

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    Just so I understand it....you are talking about the four diode rectifier on that winding prior to the electrolytics that feed that particular circuit?
     
  16. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

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    Glad to hear that you got it figured out.

    I had my Rivera out this weekend with a stereo rack effects box in the loop and got lost for hours. When I'm not playing it's dead quiet. I'm still finding new settings and sounds in that amp and I've had it for over a decade.
     
  17. Jaymann

    Jaymann TDPRI Member

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    Yes , marked as RB1 on the schematic. The + and Ac were showing continuity in both directions. It's the only thing that tested bad in that circuit. I did replace the electrolytics and diodes in that circuit as well for the few extra dollars in parts, but they all test good.
     
  18. Wally

    Wally Telefied Ad Free Member

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    JayMann, are you saying that all of the diodes test good when out of the circuit? A good diode does not show the same test results when the probes are switched around in the other direction..... confused by your explanation, I am.
     
  19. Jaymann

    Jaymann TDPRI Member

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    Sorry, I meant the diodes D7 & D8 and Capacitor C13 that come after IC1 tested good but I replaced them anyway. The 4 diode rectifier was the only thing that tested bad as the + and AC showed same results when probes were reversed.
     
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