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Sunn Coliseum PA head circuit discrepancies

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  • #1

    Sunn Coliseum PA head circuit discrepancies

    I'm doing a recap of a 60's vintage Sunn Coliseum PA head. I should have documented how the power supply was wired but assumed the schematic I have was correct. The plate resistor on pin 6 of V3 is 100k not 220k, the plate resistor on pin 1 is 47K. Pin 6 of V4 is 330k not 270k. Where they all meet at supply c I have 2 68K 1 watt resistors that I'm not sure where to place because they aren't on the schematic. Also the 18k 2 watts between A, B, and C aren't there. I have one 24k that I don't know where to place. Does anyone have a schematic that reflects these different values? I've looked all over the web and haven't seen anything. I'll attach the schematic I have
    PaulClick image for larger version Name: Sunn Coliseum PA.gif Views: 1 Size: 75.0 KB ID: 868637
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  • #2
    The amp works and you are simply recapping it? Why not leave the circuit as it is then? This could be a factory revision, it could be some sort of modification done by a previous owner, hard to say. But from your description it is just some changed resistor values and a little reconfiguration in the B+ supply.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      The only schematics I can find for the "Coliseum PA" match the one you have. I'm also reading that there was possibly a hybrid tube/SS model as well as an all SS model but found no factual evidence for this. Does your amp match the schematic in all other ways? All tube circuit, dual rectifier tubes, tube count, controls, etc.?
      "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

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        Enzo I had already gutted it before I got the new caps so I didn't realize it was different until I started recapping it. I'll just take the tubes out and wire it like I suspect it was and check the voltages. Thanks for the reply

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        • #5
          It's an old tube only head with tube rectifiers. I just thought I'd put it out there to see if anyone had a similar experience or different schematics than I had. I'll get it working one way or another

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          • #6
            Mistakes in Sunn schematics are common. Did you notice the screen resistor on V8 is 47K?
            WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
            REMEMBER: Everybody knows that smokin' ain't allowed in school !

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            • #7
              How did you make out?

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              • #8
                Made out good. As far as I know the guy is still using it 5 years later.

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                • #9
                  Originally posted by cablercdd1 View Post
                  Made out good. As far as I know the guy is still using it 5 years later.
                  Well done!

                  I am trying to buy a SUNN Studio PA head. People say there is no schematic and I should use a SUNN Coliseum PA schematic. I always wanted to own a SUNN PA head after listening to Leslie West back in the early 1970's.

                  You are very talented.

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