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Thread: all tubes light up but rectifier- Drz Z-28

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    all tubes light up but rectifier- Drz Z-28

    Hey my Z-28 started popping while I was playing and then died, after changing the fuse, all tubes light up but the rectifier. Changed it and same, all tubes but rectifier. I dont see any obvious resistors open, Im thinking its the power transformer.....what say ye?????

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    Lifetime Member Enzo's Avatar
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    The rectifier doesn;t light up? SO is ther 5VAC across the heater pins?

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    Education is what you're left with after you have forgotten what you have learned.

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    Could be a burnt wire/connection at the tube socket or a bad socket. Other than that it could probably only be a partially bad PT.

    This is it, right? Dr z z28 layout image by jaydawg76 on Photobucket

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    All power supply debug processes start off with two questions:
    1. Is the right voltage being generated?
    2. Is that voltage actually getting to where it has to go?

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    Supporting Member tubeswell's Avatar
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    Hiya mort - that layout is a home-brewed customised amp and shows a 5U4G (which is directly heated and therefore not the 'light up' type)

    Here's a Z28 schematic with a 5AR4, which will light up if everything is working properly
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Building a better world (one tube amp at a time)

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    Hi Tubes,

    I'm still pretty new to the game, and I'm aware of SS tube substitutes but I wasn't aware that some tubes don't use filaments and 'light up'. I'll look it up and I may touch on that topic again sometime

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    Supporting Member tubeswell's Avatar
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    You're doin' good mort - I only realised that stuff about directly and indirectly heated rectifiers a few days ago myself (after it was pointed out to me by someone else)

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    Building a better world (one tube amp at a time)

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    Quote Originally Posted by tubeswell View Post
    Hiya mort - that layout is a home-brewed customised amp and shows a 5U4G (which is directly heated and therefore not the 'light up' type)
    I'm not sure I understand what you're saying here. 5U4 filaments glow/light up if the tube is good. If the filament doesn't light up, it's either open or not getting current--it doesn't have anything to do with whether it's directly or indirectly heated. With a 5U4, you should be able to find continuity with an ohmmeter between pins 2 and 8 (with the tube out of the socket). Then, switch your meter to AC voltage and check for 5V on socket pins 2 & 8.

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    Quote Originally Posted by Rhodesplyr View Post
    I'm not sure I understand what you're saying here. 5U4 filaments glow/light up if the tube is good.
    I just checked one of my 5U4G amps, and so they do. What am I on about? (or rather what am I on?) (Its funny, because I've seen them with their filaments on a zillion times, but somehow when one gets a new piece of information, one can re-write history even in one's mind, in an attempt to make the problem fit the solution). Since 'discovering' they were directly heated (a couple of days ago), I was thinking that to be directly heated, they must somehow heat the cathode without a filament. But the filament must be the cathode. I think I am beginning to understand. Sorry mort - I put you wayyy wrong. (Wouldn't be the first time I've shot my mouth off badly in the middle of the night.)

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    Last edited by tubeswell; 09-19-2010 at 12:55 AM. Reason: my mind is radioactive. I need a holiday
    Building a better world (one tube amp at a time)

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