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  • Tube Help for a Neophyte

    Hey guys,

    I am not a tube guy, but, I do have a couple of tube pieces. One of them is a Redboy-Nate piece (phono stage), and the other is an old HK Prelude PC200 10w mono tube amps, with a 6V6 design (i can say it, but I don't know what it means).
    The HK amp has had a bunch of capacitors replaced, by me, over a year ago. I can't properly describe what a PITA this was.

    The problem,... The HK amp while it sounds alright, has output surges that raise and lower the volume on its own. The swings are not drastic, but, they are apparent. I didn't really notice it until I was trying to record some 78's, and the .wav forms would go large, then small, then large again.

    The only thing this amp is used for is its phono stage, and, output to a single corner speaker.
    The tubes,... a mismatched mashup of makers. I have not done anything towards replacing them.

    I guess this leads to my question,....
    Will old tubes cause this power surging?
    If not, what should I be looking for in fixing this issue?

    Anyone have some tube stock that they'd like to part with, reasonably?
    I've got to run to Orange County this morning, and won't be able to respond until this afternoon. I'll also list the tubes that the amp has at that point.
    Last edited by mfrench; 09-12-2017, 10:32 AM.
    Mike -- A SongCatcher in the Wild

  • #2
    Not familiar with your amp and will have to do some research.

    Does it raise and lower the volume in both channels?
    Turntables, Tonearms, MC & MM Phono Cartridges, SUTs, Tubes All the Way (SET, SEP and PP), Some Digital Stuff, Big Horns, Electrostats and Stand Mount Monitors, Assorted Cable and Wire. System listed here: http://www.hifihaven.org/forum/-8-mi...dated-9-3-2017

    "To thine own ears be true....."

    "Audiophiles Just Want to Have Fun....."

    Comment


    • #3
      Its a mono integrated amp, from the mid-50's.
      After I replaced the caps, it worked fine. So, that why I'm wondering about old tubes.
      Oh yeah,... Just got back in from the OC. That place sucks.

      The tubes are from left to right (from the three in a row):
      left: 5Y3GT (rectifier?)
      middle: 6V6
      right: 6V6
      There are two tubes below them in the image; both are 12AX7 phono preamp.
      I've replaced the capacitors (orange), and the group of electrolytic caps that were a multi-layer cap can; right next to the transformer.

      Click image for larger version

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      Last edited by mfrench; 09-12-2017, 02:46 PM.
      Mike -- A SongCatcher in the Wild

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      • #4
        mfrench - Cool looking amp, Mike.

        Have you examined the two 6V6 and the two 12AX7 tubes to see if one of them is gassy? The other thing to do is examine the tube sockets (and the tube pins) for corosion.
        Turntables, Tonearms, MC & MM Phono Cartridges, SUTs, Tubes All the Way (SET, SEP and PP), Some Digital Stuff, Big Horns, Electrostats and Stand Mount Monitors, Assorted Cable and Wire. System listed here: http://www.hifihaven.org/forum/-8-mi...dated-9-3-2017

        "To thine own ears be true....."

        "Audiophiles Just Want to Have Fun....."

        Comment


        • #5
          I wouldn't know what to look for.
          One of the two 6v6 tubes feels a bit loose in its base; i.o.w., the glass isn't snug, nor motion-free, within the plastic/bakelite base. It wiggles around a bit.

          I'll pull the amp, and have a look at it outside of the cabinet. I'll look into the sockets for corrosion; thanks for that.

          I was looking at tubes on eBay, but am hesitant to buy anything.
          It seems that the rectifier tube is cheap enough. The 6V6 tubes are readily available, and affordable. The 12AX7 tubes seem to run a bit more.

          Is there an order that should be followed in buying/replacing tubes?
          Suppliers that you guys use?
          Mike -- A SongCatcher in the Wild

          Comment


          • #6
            Do you have anyone close that could test the tubes? I have a good pair of 6V6 that I'll never use. No extra 12AX7 or 5U4.

            Comment


            • mfrench
              mfrench commented
              Editing a comment
              I found a local tube amp repair shop. They seem to be more oriented towards guitar amps, but, they do offer tube testings and replacements. They seem to be well liked as a service provider (in online reviews). I'm going to contact them today, and, see what they offer.

          • #7
            Originally posted by opa1 View Post
            Do you have anyone close that could test the tubes? I have a good pair of 6V6 that I'll never use. No extra 12AX7 or 5U4.
            Good thought, Mark.

            I'll see if I have any spare 5U4s around here. I know I have spare 12AX7s.

            I get my tubes from Mike Sanders at Quicksilver Audio. If Mike doesn't have a particular tube I need, I've clicked on the banner ad for The Tube Store. Got my 5751s from them.
            Turntables, Tonearms, MC & MM Phono Cartridges, SUTs, Tubes All the Way (SET, SEP and PP), Some Digital Stuff, Big Horns, Electrostats and Stand Mount Monitors, Assorted Cable and Wire. System listed here: http://www.hifihaven.org/forum/-8-mi...dated-9-3-2017

            "To thine own ears be true....."

            "Audiophiles Just Want to Have Fun....."

            Comment


            • #8
              Hi guys,

              Dealing with planting a 2:1 slope with ground cover, and I'm a wee bit off plumb right now.

              After holding mysef up on that slope,.. I took the amp out, and cleaned the contacts with some contact cleaner that I have. I also ran some dentaured alcohol into this tiny port on the on/off-volume pot. I then ran it up and down a billion times. In doing that, it seems that maybe the issue was in the pot. The tube contacts looked totally clean on the tubes, and my flashlight inspection didn;t raise any conerns in looking into the onboard tube mounts.

              Audrey is spinning my Ella Fitzgerald 78 collection right now, and its sounding mighty fine. I haven't heard these for quite a while. So its a nice to spin with Audrey again.
              Thanks!

              I have some more questions, but need to remember them first.
              Last edited by mfrench; 09-13-2017, 07:12 PM.
              Mike -- A SongCatcher in the Wild

              Comment


              • #9
                I remember now...
                In the tube name sequence, as example, 6V6, I see various extensions to the model numbering, such as, 6V6GT
                How crucial is this in buying correct tubes?
                Is a 6V6 just a base model, and the 6V6GT the hot-rodded version, updated version? Are they cross-compatible?

                I use 6V6 as the example, but I see this same thing across a number of different tubes; 5Y3, 5Y3GT
                Mike -- A SongCatcher in the Wild

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