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    What would ruin a GZ34 tube and can it be protected?

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    heyraz

    Posts : 58
    Join date : 2011-10-26

    What would ruin a GZ34 tube and can it be protected?

    Post by heyraz on Mon Nov 07, 2011 2:37 pm

    I'm rebuilding a ST-70 using the original transformers and NOS/used Mullard EL34's (everything else will be new) and became concerned when I read that other users have had their rectifier tubes destroyed most likely by a faulty quad cap. As my GZ34 (Mullard f31 fat base) is arguably one of the most valuable tubes I own, I'd like to know what situations can take it out and if it can be protected. Thanks. Rich

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by tubes4hifi on Mon Nov 07, 2011 4:40 pm

    there are SEVERAL posts on this forum about this topic, just do a search, there is a simple diode mod that will protect the tube
    OK, not so easy to find, although it's been posted 3 or 4 times, here it is again . . . .



    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by heyraz on Mon Nov 07, 2011 7:03 pm

    Thanks, I should have searched first. Rich

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by j4570 on Mon Nov 07, 2011 9:58 pm

    After rebuilding, I would NOT start it up using a Mullard. Buy a cheap Ruby rectifier or something else just in case......

    And make the mod. I need to open mine and do it. I didn't have any diodes when I was building mine.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by heyraz on Mon Nov 07, 2011 10:27 pm

    Thanks. I planned on using cheap tubes everywhere until the amp has proven itself. I saw that diode mod on another amp's schematic and it got me wondering. When I read about a rectifier getting taken out in this forum, all I could think about was what if it happened to me. I think I've also seen resistors used to reduce the rapid inrush of current but I'm not sure about that. I need to do some more research. Thanks again.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by heyraz on Mon Nov 07, 2011 10:39 pm

    Just a thought...since I'll be using a brand new Quad cap (as well as all other caps), is there any value in using a Variac to bring this thing to life?

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by Luddite on Mon Nov 07, 2011 10:54 pm

    heyraz wrote:Just a thought...since I'll be using a brand new Quad cap (as well as all other caps), is there any value in using a Variac to bring this thing to life?

    Absolutely, using a Variac to slowly power-up a newly built project is always a good idea. Go slowly and watch for smoking, swelling capacitors, glowing plates, etc. If any appear shut it down, otherwise continue bringing it slowly up to operating voltage, allow it to stabilize for about 10 minutes and then set the output tube bias. After about 15 minutes check the bias again and adjust as necessary. You should then be ready for some music!

    Best Regards,
    Charlie

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: What would ruin a GZ34 tube and can it be protected?

    Post by heyraz on Mon Nov 07, 2011 11:21 pm

    Charlie, Thanks. Now I wish I had a variac. I read somewhere about making a "poor mans" variac using light bulbs in series with the device. I'll have to read more closely but I think the idea was to start out with a 15 watt bulb, wait for it to go out, then replace it with 30 watts, etc.. Do you have any thoughts about this method or should I bite the bullet and pick up a used variac?
    Rich

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