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Post by jazzguy on Feb 24, 2024 16:04:41 GMT -5
the fuse in my '66 Vibrolux Reverb bit the dust last night
I don't have any 2 amp fuses, but have a few 1 1/2 ampers, are they ok?
not sure if just the fuse went bad or maybe a bad tube rectifier or power tube took it out
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Post by Leftee on Feb 24, 2024 20:09:13 GMT -5
You could do that, but the amp probably has an issue if it blew the 2A.
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Post by jazzguy on Feb 24, 2024 20:29:41 GMT -5
Yeah, I'm hoping it's no worse than a bad tube, my tech is great but an hour away and very expensive.
I'm guessing a 1.5 fuse will fry a little sooner than a 2 but as you said if it's a component it'll fry it regardless.
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Post by Leftee on Feb 24, 2024 20:34:06 GMT -5
Just be aware that what cooked the original fuse could possibly damage the amp in addition to blowing the next fuse.
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Post by jazzguy on Feb 24, 2024 21:27:26 GMT -5
I'm no expert but if it's a transformer wouldn't the damage already be done?
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Post by LTB on Feb 25, 2024 8:11:29 GMT -5
Yes, but you are banking on it being a transformer. It could be something else.
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Post by jazzguy on Feb 25, 2024 8:55:44 GMT -5
I know it could be a number of things, they can be addressed at minimal cost, but I believe a fried transformer would be worst case.
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Post by jazzguy on Feb 25, 2024 16:50:53 GMT -5
Well I put a new fuse and rectifier in and it powers up. But then I put the old rectifier in and it powers up but the tube glows pretty brightly, not sure if it's going bad or not.
Our last gig was in an old church basement, many of the outlets were old ungrounded, maybe a power surge fried the fuse.
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Feb 27, 2024 6:37:31 GMT -5
All valve amp users face this scenario now and again, so I suggest it's a really good idea to get fixed up with a light bulb limiter and a selection of bulb wattages.
Incandescent or halgen bulbs, most useful wattage will be about twice the amp's rated power output.
So in this case, maybe 100W incandescent or 80W halogen.
It'll save on fuses but most importantly massively reduces stress on the amp, especially those vintage transformers.
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Post by jazzguy on Feb 28, 2024 2:43:07 GMT -5
All valve amp users face this scenario now and again, so I suggest it's a really good idea to get fixed up with a light bulb limiter and a selection of bulb wattages. Incandescent or halgen bulbs, most useful wattage will be about twice the amp's rated power output. So in this case, maybe 100W incandescent or 80W halogen. It'll save on fuses but most importantly massively reduces stress on the amp, especially those vintage transformers. Was hoping you'd chime in pdf64.I may get around to building a limiter but in the meantime since I replaced the fuse and it seems to be working ok do I need to worry or can I save my concerns if it happens again in the near future? just a note, the flashing on the old Mullard GZ34 looks like it's dissipated somewhat and it seems to be glowing relatively brightly, is that a sign it's on it's way out which might have caused the fuse to blow? Any comments welcome, thank you |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Feb 28, 2024 6:51:17 GMT -5
In the short term you seem to be ok, but restocking with some 2A fuses would be a good idea. 1.5A might pop anyway when you're pushing the amp at a gig, regardless of an actual fault. Some back-up / protection silicon diodes for the valve rectifier would be very beneficial, see immortal amp mod link below. They stop all that shorting out and fuse blowing nonsense that can plague old valve rectifiers, and keeps them working until they just wear out. Kinda like run flat tyres  By that, they take the stress of such fault current incidents off the transformers and HT caps. Be aware that the blown fuse may be due to an intermittent fault in a 6L6 output valve, that again might not manifest until the amp gets pushed a bit or a lot. I wouldn't be concerned by the old Mullard's flashing being less than perfect or the heater element appearing bright. But if you want to play it safe (understandably), put it safe to one side until the silicon back up diodes are fitted. www.premierguitar.com/the-immortal-amplifier-mod |
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Post by LTB on Mar 4, 2024 4:39:16 GMT -5
All valve amp users face this scenario now and again, so I suggest it's a really good idea to get fixed up with a light bulb limiter and a selection of bulb wattages. Incandescent or halgen bulbs, most useful wattage will be about twice the amp's rated power output. So in this case, maybe 100W incandescent or 80W halogen. It'll save on fuses but most importantly massively reduces stress on the amp, especially those vintage transformers. Was hoping you'd chime in pdf64.I may get around to building a limiter but in the meantime since I replaced the fuse and it seems to be working ok do I need to worry or can I save my concerns if it happens again in the near future? just a note, the flashing on the old Mullard GZ34 looks like it's dissipated somewhat and it seems to be glowing relatively brightly, is that a sign it's on it's way out which might have caused the fuse to blow? Any comments welcome, thank you I built one with a cylindrical Halogen bulb. I put a piece of 1/4” dark smoked glass in front to prevent it from blinding me in a short circuit situation. In retrospect I probably could have just used a piece of thin aluminum plate to block blinding light. I used to aluminum L brackets from hardware store to hold it in place. It allows about 3-4 amps (if memory is correct as that was 20 years ago) before it starts to drop enough voltage across the bulb to start illuminating and at 5 or 6 amps glowing brightly. |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 4, 2024 6:32:40 GMT -5
I built one with a cylindrical Halogen bulb. ... It allows about 3-4 amps (if memory is correct as that was 20 years ago) before it starts to drop enough voltage across the bulb to start illuminating and at 5 or 6 amps glowing brightly. Whatever works for you, anything is better than nothing, but I fear that may be rather too beefy to provide much actual current limiting for most valve guitar amps. Maybe perfect for SVT type monsters though |
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Post by LTB on Mar 4, 2024 15:52:15 GMT -5
So what do you suggest?
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 4, 2024 16:47:53 GMT -5
Bulb wattage about twice the rated power ofthe amp it's feeding is a good compromise. About a 100W bulb generally works out well. |
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Post by LTB on Mar 4, 2024 23:43:59 GMT -5
Thank you for your input, Been a few years since I used it. I was going on memory of something I made in 2004-2005. It seemed to work fine when I used it troubleshooting a 1965 Super Reverb that was blowing fuses. It lit brightly but didn’t blow the fuse while using it.
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 5, 2024 6:19:48 GMT -5
I think it's a good idea to use a light bulb limiter at initial power up whenever there's new, unknown or suspect output or rectifier valves in the amp.
Consider that a vendor can test and burn in valves until he's confident to have weeded out the early failures. But then they get shipped, and the delicate structures inside the valve can become dislodged / loose, and problems can then manifest when high voltage is applied.
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Post by LTB on Mar 5, 2024 22:51:24 GMT -5
Yeah, also used it after a complete cap job and brought the voltage up slowly. |
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