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Speaking of amps that run tubes very hard....

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  • #1

    Speaking of amps that run tubes very hard....

    I have a 1974 Alamo Montclair Reverb 2562, cathode biased with no schematic. I did a re-cap and chased out a demon or two. When I measured the two Raytheon 6V6s (one metal, one glass) I was surprised to see them running at 18.5 and 16.5 watts. The 195 ohm cathode resistor is sound, but I don't know if it is the original or intended value.

    I'm at first tempted to "fix it", but I don't have a suitable resistor to play around with, and that was not the customer complaint. The amp sounds really good, so I guess I am going to go with the idea that this is how it has always been, and those American tubes can take it. I did sub a new set of JJs for long enough to measure them, and they drew even a tad more.

    It bothers me, though.
    It's weird, because it WAS working fine.....
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  • #2
    Here is what I have for the Montclair.

    Schematic calls for a 330 / 5 watt cathode resistor.

    alamo-montclair-amplifier-schematic.pdf

    I am not a big fan of the metal can 6V6 tubes.

    Comment

    • #3
      I'm not a fan of ANY tubes I can't see the guts of...

      Justin
      "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
      "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
      "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

      Comment

      • #4
        Originally posted by Justin Thomas View Post
        I'm not a fan of ANY tubes I can't see the guts of...

        Justin
        Ah, you can't discriminate based on looks, what about locktals, 7 pins, acorns, nuvistors, compactrons? Seriously, those metal 6v6's have the same spec as the glass. The metal 6l6's have the original spec of 19W dissipation. They all do get very hot though

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        • #5
          It's not about the specs. It's about the fact that I can't SEE what's going on inside the tube: redplating, blue glow vs. purple glow, arcing, melting screens, lost vacuum, etc.

          Justin
          "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
          "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
          "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

          Comment

          • #6
            That schematic is not even close to what I have here. To start with this is a hybrid amp, only tube PI and outputs. Also it has cathode bypass cap, as well as another wire connecting the cathode to something in the preamp that I can't tell what it is.
            It's weird, because it WAS working fine.....

            Comment

            • #7
              Originally posted by Randall View Post
              as well as another wire connecting the cathode to something in the preamp that I can't tell what it is.
              Some sort of negative feedback loop?
              Or some sort of bias network for something?

              Justin
              "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
              "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
              "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

              Comment

              • #8
                http://music-electronics-forum.com/a...9&d=1526423358

                Comment

                • #9
                  OK, that looks like the right one. Sure is difficult to read, tho. I THINK that is a 195 ohm cathode resistor, in which case the amp is as it was intended.

                  Another thing to note here is the .02 coupling caps from the PI to the 6V6s are big ceramic disks! I guess they didn't buy the orange drop/Mallory/mustard cap thinking.
                  It's weird, because it WAS working fine.....

                  Comment

                  • #10
                    Originally posted by Randall View Post
                    Another thing to note here is the .02 coupling caps from the PI to the 6V6s are big ceramic disks! I guess they didn't buy the orange drop/Mallory/mustard cap thinking.
                    Are they doing their job and keeping DC off the 6V6 grids?
                    Originally posted by Enzo
                    I have a sign in my shop that says, "Never think up reasons not to check something."


                    ​

                    Comment

                    • #11
                      Very good point. Indeed they are.
                      It's weird, because it WAS working fine.....

                      Comment

                      • #12
                        Then it is probably as designed, if that 195 ohm cathode resistor is the stock value. It's impossible to tell from the 2562 schematic.
                        The other Montclair (all tube) schematic shows a 330 ohm there and the voltages given work out to around 12W per 6V6.
                        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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