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Old 12th May 2009, 08:27 PM   #1
newtube is offline newtube  United Kingdom
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Unhappy simple se blowing rectifier and fuse

Guys, i just finished assembling my simple se and on powering up it is fine for about 5 seconds then the rec tube crackles and it blows the fuse, this happens with all tubes fitted or just the rectifier. . . .
Any pointers as to what can cause this?
I'm so fed up as iv'e been looking forward to this all day

p.s, this happens even if i swap the rec tube for another
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Old 12th May 2009, 08:43 PM   #2
rknize is offline rknize  United States
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Can you tell us more about your setup? What power transformers? What B+ voltage do you see? Any pictures of the PCB? Have you tried with the output transformers disconnected? Sounds like a short somewhere or an incorrect resistor value or something along those lines. Check your work, especially the resistors and the polarity of the capacitors in the power supply section.
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Old 13th May 2009, 07:30 AM   #3
DimZ is offline DimZ  Greece
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... wrong post
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Old 13th May 2009, 12:12 PM   #4
newtube is offline newtube  United Kingdom
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The transformer is a hammond 373 bx, im using 6l6gc tubes and a gz34 rectifier tube, no freds, and the output trannies are not yet connected.

I can't measure the b+ at the mo as my meter batteries are flat!

Everything looks fine, the amp powers up fine without the rec tube in, if the rec tube is installed the tubes glow for 5 seconds then the rec tube crackles and blows the fuse
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Old 13th May 2009, 12:36 PM   #5
vuohi is offline vuohi  Finland
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Are you using JJ GZ34s? I had a faulty one, and searching the web I discovered that there have been relatively many of them failing. Apparently a bad batch or something.
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Old 13th May 2009, 12:42 PM   #6
newtube is offline newtube  United Kingdom
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It is indeed a jj gz34, i tried 2 of them.
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Old 13th May 2009, 01:42 PM   #7
vuohi is offline vuohi  Finland
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My faulty JJ had some metal flakes inside the bulb after the failure. You could check the valves for obvious visual faults like those flakes or misaligned parts. And of course, check your solder joints and double check parts values and possible shorts.
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Old 13th May 2009, 01:56 PM   #8
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Default One other possibility causing fuse blowing...

Double check the installation of the high tension rectifier filter capacitors to assure they are installed correctly. If either of these accidentally got installed backwards, this will blow the fuse once the rectifier tube goes into conduction and begins to try and charge them. Thus, be sure the capacitors (+) terminal is oriented to the correct pad on both capacitors.

Doug
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Old 13th May 2009, 05:08 PM   #9
newtube is offline newtube  United Kingdom
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does c3 cap have a polarity?
i notice the lettering on mine is facing the opposite way to the tubelab pics
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Old 13th May 2009, 08:20 PM   #10
n_maher is offline n_maher  United States
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Quote:
Originally posted by newtube
does c3 cap have a polarity?
i notice the lettering on mine is facing the opposite way to the tubelab pics
No, C3 is a small film cap and does not have a polarity.
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