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Dirty-South Blues Harp forum: wail on! >
Amp Trouble-Help?
Amp Trouble-Help?
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NiteCrawler .
100 posts
Jan 23, 2011
7:06 AM
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Good Morning Folks,I was hoping to get some input on an amp that I own which J.Kinder modded for me around 8 or so yrs ago.Its an Ampeg VT 40 4 ten combo which was left on(2 weeks) when I was away on vacation a while back and does,nt power up.(yes I changed the fuse)I have a # of other amps so she,s been on the backburner for quite a while but I want want to get her back up and running.(BTW she,s a screamer when working,just remember the back brace)Actually before S.R.Norcia started playing through S.Juniors he played through one of these,with the Kinder mod to boot.When I spoke to him at one of they,re shows and told him that I played through the same beast he was blown away.Anyway enough of my rambling,would anyone know what possible damage could have been inflicted on the amp because of this f-up?(switch,tubes,p-trannys,etc.)Any advise would be very much appreciated.I figured I,d get some input here possibly before sending it out.(moneys tight,"Its Bad You Know")Thanks,NC
Last Edited by on Jan 23, 2011 7:08 AM
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5F6H
489 posts
Jan 23, 2011
7:34 AM
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So you changed the fuse & the amp powers up, without blowing the fuse, just no sound?
If the fuse keeps blowing, pull out all the power tubes & try again, if it powers up without power tubes & doesn't blow a fuse things look slightly more hopeful (rectifier & power transformer should be OK)
Whichever way you look at it, you need a tech. The only way to know what is specifically wrong is to open it up & take some measurements. To check the Power transformer means disconnecting all the secondaries, isolating them & seeing if the fuse holds (a job for a tech, as you will have live wires exposed).
Most amps should be up to working temperature within a few minutes, beyond that the longer you keep them on, the hotter they get, any amp should last a set/gig/even an afternoon of jamming without suffering heat related issues, but leaving it on for 2 weeks is pushing it. Instrument amps don't have power transformers designed for continuous operation.
The hotter your amp is biased the hotter it will get, cathode biased amps (the VT40 is fixed bias) could do with being switched off during breaks to let them cool down, as cathode bias usually means hot idle currents.
Maybe your tubes died & took the fuse with them, maybe they just killed the fuse & the rectifier diodes, maybe the B+ winding on the PT burned out & the tubes survived, maybe the the tubes, rectifier, & PT are all shot...? All these are possible, plus other diagnosis. I wouldn't keep trying to power up with the old power tubes until other causes of failure are eliminated/identified. If you keep powering up with shorted power tubes you could be risking damage to the power transformer if it is not damaged already.
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chromaticblues
513 posts
Jan 23, 2011
7:44 AM
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Your right its probably bad. I'm just guessing, but I would say one section of your power transformer couldn't take the heat from being on so long. It really isn't hard to figure out, but someone is going to charge you an arm and a leg. On the other hand maybe a tube melted. Was the fuse blown? If yes try a new rectifier tube. If that doesn't do it then power tubes. If it keep blowing fuses. Your screwed.
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Greg Heumann
1013 posts
Jan 23, 2011
11:29 AM
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Well?
5F6H's diagnostic progression makes sense.
Don't assume the worst. If you're lucky its just a tube.
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/Greg
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NiteCrawler .
102 posts
Jan 24, 2011
3:11 PM
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Well guys I experimented yesterday after heating up my refridgerater yesterday,10 to 15 degrees here in N.J. anyway,it didn,t power up as said but I moved the standby switch back and forth around 10 times and...........the standby light came on making for a happy moment so I grabbed a cable,thumbed the end a couple of times to hear contact,grabbed my bullet and.........power down again.Booo..I could possibly try to install a new switch but think I may just take it to a tech and get the dirty lowdown.On the bright side my evening ended on a good note when that loud mouth coach got beat by the Steelers.(Not so bad of a day I guess for now,wait until he tells me what its going to cost to fix it)Thanks Again for your input guys,much appreciated.
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