#1
Blew one, replaced it, blew another....Now, lookin around on the web I've seen different advice. The first stop is to replace the power tubes, since it has a solid state rectifier but a quick question. Should I have heard any audio evidence before the power tubes caused a fuse failure? Both times I was happily jamming along, followed by a few seconds of the amp fizzling out. I haven't had any other issues with the amp whatsoever and it's very possible the amp is due for a tube swap.

Another thought I had.....I had a guitar cable that's a little squirrelly running from the footswitch to the amp. It works once it's set in place, but a little wiggling shuts it down. Since the push button channel selectors on the face of the amp are almost always different than what the footswitch is sayin it could cause rapid channel/reverb/master volume switching. Is this something that could cause a fuse to blow?
#2
Usually tubes start to sound weak and thin before they blow, sometimes the pop and fart, sometimes they just die without warning. There is no universal symptom, sometimes they will just blow fuses. Try your spares. If you don't have spares, why not?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#3
Quote by Cathbard
If you don't have spares, why not?

Quote by Cathbard
Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#4
Quote by Cathbard
Usually tubes start to sound weak and thin before they blow, sometimes the pop and fart, sometimes they just die without warning. There is no universal symptom, sometimes they will just blow fuses. Try your spares. If you don't have spares, why not?


I have 2 amps and I go back and forth between them and I don't gig out regularly.

I have all new power tubes for both amps on their way here along with a handful of 12ax7s.

I'm just double checking to make sure my reasoning is sound. Hate to send it off unnecesarily.
#5
Even if it's not the tubes you should have spares so you've wasted nothing.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#6
what Marshall is this? If it continues to blow fuses then something is wrong. Did the fuse blow after putting new tubes in or did you put new tubes in because the fuse blew (never mind - looks like the latter)? I'd take it to a tech for a once over. Which fuse is blowing? I can't imagine a footswitch cable/jack causing a fuse to blow but Cath is the amp expert here not me.
#7
Just FYI, if a fuse blows something is wrong. You shouldn't just replace it and try again. Fuses safeguard your amp from danger. Continously replacing and blowing them is saying 'come on amp, let a little danger through.' Bad idea.
Quote by Cathbard
Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#8
Quote by 311ZOSOVHJH
what Marshall is this? If it continues to blow fuses then something is wrong. Did the fuse blow after putting new tubes in or did you put new tubes in because the fuse blew (never mind - looks like the latter)? I'd take it to a tech for a once over. Which fuse is blowing? I can't imagine a footswitch cable/jack causing a fuse to blow but Cath is the amp expert here not me.


It's a JVM 50w combo.

I blew a fuse, tried a replacement, it blew after a couple 1 or 2 hour playing sessions, and I haven't tried it since going by the best advice I could find. Finally gotten around to ordering replacement tubes and am trying to reassure myself that it's the problem.

The footswitch thing was just a theory. I would think rapidly changing the channels could cause some harm, but I don't really know much about amps, obviously.
#9
Quote by tubetime86
Just FYI, if a fuse blows something is wrong. You shouldn't just replace it and try again. Fuses safeguard your amp from danger. Continously replacing and blowing them is saying 'come on amp, let a little danger through.' Bad idea.


I blew one, and tried another to make sure it wasn't just the fuse failing. I'm not feeding the amp fuses.
#10
Like Cath said, a tube dying probably wouldn't blow the fuse (but it is possible) as the other tube would take the load (although still not good). Is it the mains fuse or an HT fuse? Maybe get a bias probe - but I'd take it to a tech.
#11
if its something your not experience with, i suggest u take it to a tech and have em scope it out. most tech's will credit the charge for the diagnostic toward the repair.
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#12
If you had spare tubes you'd already know if they were causing the problem. You gotta have spares, man.

And of course they will bill you for diagnostics time - that's the most time consuming part usually. You don't expect him to work for free do you?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Dec 1, 2011,
#13
Quote by 311ZOSOVHJH
Like Cath said, a tube dying probably wouldn't blow the fuse (but it is possible) as the other tube would take the load (although still not good). Is it the mains fuse or an HT fuse? Maybe get a bias probe - but I'd take it to a tech.


He said sometimes they will blow fuses?


Hope I don't have to take it to a tech. Where's I'll take they'll have to send it off.
#14
It could be a few things. Tell me, does it hum before it fails?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#15
Quote by Cathbard
It could be a few things. Tell me, does it hum before it fails?


Not really. Both times the fuse(one where the power cord plugs into the amp) blew I was playing along and it kinda fluctuated up and down slightly and boom went the fuse.


When I did an online search for the problem, most people pointed at a bad rectifier tube, which my amp doesn't have to my understanding, or a bad power tube. It's definitely possible that the tubes have reached the end of their life, so that seemed like the best place to start troubleshooting.


Also, is my footswitch theory completely ridiculous? I would think very rapid channel changing could **** something up. Think about a guitar cord on the fritz and how a little wiggle here or there will turn it off and then back on. That's
Last edited by MAYNARD at Dec 1, 2011,
#16
Quote by MAYNARD
I blew one, and tried another to make sure it wasn't just the fuse failing. I'm not feeding the amp fuses.

Oh ok, that's not a big deal then... I just got the impression you were continuously doing that.
Quote by Cathbard
Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#17
If it was a footswitch it would only really be affecting preamp tubes and even then I doubt it will do what you are describing.
If it's not the power tubes I'd be replacing the filter caps in the power supply next. They can sometimes go short circuit dragging the power supply to ground. That will blow fuses and may only happen after they get hot. That's why I asked if it hummed. If their dc resistance drops gradually with heat you'll often hear an increase in hum just before they die.

Edit: Filth inside the chassis can do it too. Crap that gets less resistive with heat. A good clean will fix a lot of things. You'd be surprised how many.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Dec 1, 2011,
#18
Alright cool....Thanks for all the help guys. Tube guy(Fedex) is supposed to be here any time with all my tubes. Got some replacements for the Marshall and both kinds for my Egnater. I'll definitely be stockin up on some backups asap, I've just never absolutely had to have them.


I just pulled the tubes and was looking them over and one seems to have some tiny white flakes that look almost like ashes. The other tube has one black spec, but it looks almost like its stuck to the glass. Is that some sorta residual thing from manufacturing, or could that be a sign of trouble?


Good idea on the cleaning. I've never had the amp opened up, but I've used the canned air to blow the places I could reach.
Last edited by MAYNARD at Dec 1, 2011,
#19
The one with the white flakes is worrying. 10:1 it's the problem.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#20
It also depends on where the fuses are in the circuit. It's entirely possible that there's something wrong with your power supply. And yeah, the white stuff doesn't sound right either.

EDIT: and I doubt it's your footswitch.
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