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Old 03-13-2013, 11:54 PM   #1
lightningjoe88
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Lightbulb Tube amp problem (picture) I think it's a fuse

Back again,
So I was playing my amp just fine a few days ago and it worked fine, but I go to turn it on the next day and it turns on but the tubes won't even glow. It turns on but won't produce sound. I noticed it got quite hot when I played it a couple days before and thought maybe some sort of fuse went out, so I asked some questions here and took in advice and checked out my amp's innards. From what I saw, there seems to be a blown fuse but I'm not 100% positive. I took extra pictures too in case any of you notice something that I just overlooked, but I their size exceeds the limits so I don't know how to post the rest. Thanks

- Joe
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Old 03-14-2013, 12:03 AM   #2
trashedlostfdup
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NEVER judge a fuse on how it looks. test continuity with a meter. no continuity it is blown. takes 15 seconds. if you don't have a meter buy one and probably some new fuses (a few for all of the different amp types you have IMO)

looks can fool on rare occasion, has happened to me working on drag care as well as popping fuses on the JTM45 i buily. rare, but do check.
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Old 03-14-2013, 12:17 AM   #3
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I don't have a DMM at the moment. I've been needing to buy one for a while now. Is there a way I can look up the schematics and find out what the fuse it for? Could bad tubes cause overheating?
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Old 03-14-2013, 12:18 AM   #4
R45VT
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It looks bad, however visually is never te best way to check. If you don't have a volt meter you can buy one for 20 bucks.

This is your jVM from the other thread right?

You probably need to replace your powertubes if the fuse blows again.

Last edited by R45VT : 03-14-2013 at 12:25 AM.
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Old 03-14-2013, 12:21 AM   #5
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Yeah, the JVM. My bad. I'm going to try and borrow a DMM if I can..... so I can spend more money on gear of course. Haha. I'll get one soon guys, I promise!!!
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Old 03-14-2013, 12:28 AM   #6
R45VT
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I think the JVM410 bias is at 70mv. Do you see the 3 pins for checking the bias? Each side should be set at 70mv... If I remember correctly...

If you are unsure, or uncomfortable you will need to take it to a tech.

High voltages are present on tube amps and could kill...
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Old 03-14-2013, 12:31 AM   #7
lightningjoe88
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Just noticed this too, lookin at R81.
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Old 03-14-2013, 12:37 AM   #8
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Quote:
Originally Posted by lightningjoe88
Just noticed this too, lookin at R81.


time to strip her down. looks like the fuze didn't pop fast enough.

another note is when getting replacement fuses, there are sloblo and fast blow as well. they are not interchangeable.

i have an ampeg lee jackson that burned up something, but now i don't remember where that it was and can't find it.

R45vt will give you some useful tips, he helped me out in a quite few spots in the blue voodoo modding.
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Old 03-14-2013, 12:44 AM   #9
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I'll look at the schematic later. The PCB looks like it got hot around the left fuse clip on 4.

If 81 is in the bias or powertube related you are going to need to take it to a tech. I'll see if I can't find a schematic later and post back up.

Anything else look like it got hot?
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Old 03-14-2013, 12:49 AM   #10
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Old 03-14-2013, 12:51 AM   #11
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Looks connected to overheating from what I can tell.
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Old 03-14-2013, 01:07 AM   #12
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In that schematic its part of the HT to float the heaters by the center tap.

I would take it to a tech for repair.

F4 is one of the fuses for the heaters.
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Old 07-04-2013, 10:27 AM   #13
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Hi everyone, I thought I'd post this in here as people seem to know what they're on about. I switched on my amp the other day and the power lights came off then went off again. So I switched it off by the plug then plugged it into a different plug just to see if it was the mains socket that had tripped. However when I plugged it into another mains plug and switched it on there were no power lights on, but the valve were glowing. Any advice what the problem maybe???
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Old 07-04-2013, 10:47 AM   #14
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Quote:
Originally Posted by Diamondrag
Hi everyone, I thought I'd post this in here as people seem to know what they're on about. I switched on my amp the other day and the power lights came off then went off again. So I switched it off by the plug then plugged it into a different plug just to see if it was the mains socket that had tripped. However when I plugged it into another mains plug and switched it on there were no power lights on, but the valve were glowing. Any advice what the problem maybe???

It still works correct?
Is it the Bugera?

I have a Bugera 333 head and the standby light burnt out, but the amp still works fine.
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