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Kay 705 tube help!!

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  • Kay 705 tube help!!

    Hey guys,

    I posted this at Ampage, but maybe everyone is using this site now, so I'll try here:

    I've got a Kay 705 that I'm trying to get working. One of the tubes shattered at some point. It says Sylvania 913 MJF on the base.

    I was told this amp used a 6l6 and that a 5u4 would be the rectifier. I tried a 5u4 and it blew the tube. :-/ Here is what I know about the tubes from left to right looking at the back of the amp:

    There is not a 12at7 like I originally thought. It is a smaller tube. Made by Sylvania and the only marking on it is 909 and APD. I have no idea what this means.

    The next tube is a 50L6GT. Not sure if this is related to a 6L6 or not.

    There is something that looks like a covered tube, but I can't get the cover off and don't want to break it. Anyone know what it might be?

    The final socket is the one I'm trying to find a tube for that fried a 5U4 in a heartbeat (and left my Dual Rectifier lifeless).

    Any help is really appreciated. I'm pretty handy around convential amps, but I don't know what these tubes are or where to get them.

    Thanks!

    Mike

  • #2
    The rectifier is probably a 35Z5.That's what's commonly used with a 50L6 power tube, and it has a 35 volt filament. All of the tube filaments are series connected in a design of that type; adding them all together comes out somewhere close to the line voltage, so the expense of a filament tranformer can be eliminated. Most such amps have no power transformer at all, though a few have a small one for the B+ only. The 50L6 is an older and lesser tube than the 6L6, with a 50 volt filament. Guessing isn't a good idea with that kind of an amp, Mike; you really need to get the right tubes.
    Last edited by tboy; 05-28-2006, 03:16 AM.
    -tb

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    • #3
      Originally posted by tboy
      The rectifier is probably a 35Z5.That's what's commonly used with a 50L6 power tube, and it has a 35 volt filament. All of the tube filaments are series connected in a design of that type; adding them all together comes out somewhere close to the line voltage, so the expense of a filament tranformer can be eliminated. Most such amps have no power transformer at all, though a few have a small one for the B+ only. The 50L6 is an older and lesser tube than the 6L6, with a 50 volt filament. Guessing isn't a good idea with that kind of an amp, Mike; you really need to get the right tubes.
      Thanks for the info. I got a response on ampage as well with the same diagnosis. I had tried the 5u4 based on someone elses suggestion. They thought it ran a 6l6, which obviously it doesn't. I hadn't discerned the 50L6 marking, but it it is all making sense.

      If I put an incorrect or damaged rectifier into an amp, what kind of damage can be done to the amp?

      Thanks for your help!

      Mike

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