So last night we were playing a gig and my friend wanted to borrow my head (6505+). He plugged it into his Marshall cab and started playing... 2 songs in the sound cuts out. Upon inspection, I noticed he plugged the head into the 4 ohm input in the Marshall (1960BV) but the head was still on 16 ohm. The standby switch doesn't light up anymore and I replaced the fuse with a 5V fast-action one (the guy from Quest Musique told me this would work)... but it still doesn't work. I'm afraid that something else may be burnt out, any suggestions?
I don't know what to suggest, but make sir your friend PAYS FOR IT!
HA... Will do, but before it gets to that point... I'm hoping there is an easier fix.
Tube amps do not like mismatch ohms on cabs. SS stuff is alot more tolerant. Hope your friends got some cash.
Thats why i always check my speaker connection like 15 times before i even turn on my amp after readjusting and moving it. All it takes is something to bump a switch and poof its done for.
So there's no simple fix like a fuse replacement or anything? What are the possibilities... Like which component is most likely to be fried? After the fuse cuts out, isn't that supposed to 'save' everything else? Are there multiple fuses? Before I (or my friend) drop a couple hundred to fix this... I'm just hoping anyone knows for sure if anything can be done before I take it in.
That is why I don't let anyone borrow my stuff. My friend asked if he could borrow my squier, and I was like no.
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there are multiple fuses in that head, not only the mains, but there are fuses on the board itself too. Hopefully it's not your OT, but that's a pretty large impedance mismatch. Probably best to bring it to a tech.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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Argg... Actually, I recall differently now, the head itself was on 8 ohm, not 16 ohm. I guess that still doesn't make a difference... maybe less damage..?
hopefully, that's not a huge mismatch. Getting pushed to stage volume though, I dunno. Does the head have an HT fuse and mains, or only mains fuse?
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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I'm not sure, I just bought the thing a couple weeks ago so I'm not entirely familiar with it. I'll see if I can dig up some schematics on it... it's a Peavey 6505+ if you were feeling extra helpful. Another thing, the power LED comes on but regardless of where the standby switch is set, it's off. And at the time he was using it, the volume on the lead channel was set to 3, it was being mic'd.
I looked at your manual, but I didn't see any HT fuse labeled. You know what, you may want to post over on the forum, or contact Jerry directly at FJA Mods. He does great work on 5150's, I know of a lot of people that have his mods on their amps, and all love them. He's very friendly, and knows just about everything dealing with the 5150's, he's helped me quite a few times when I had questions. He might be able to tell you straight off what the light not coming on could mean, judging from the circumstances when it died.

"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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Could it be a tube? I believe impedance mismatches put extra strain on the tubes.

Could also be the second fuse, but then again I don't know much. I suggest you try what Erock said, he seems to know his stuff.
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Alright, I'll send him an email, thanks for the help by the way, I really appreciate it. I don't wanna take it in and have some tech screw me big time when I just need to replace a couple $3 fuses or something.

I'll let you guys know what the deal is so if anyone else happens to be in this situation... they'll know what to do.
1st off, you don't want a fast action fuse in your amp. Check your owners manual and find out what fuse it's supposed to have. Get a whole box of them and put one of those in.

Lots of Marshall amps blow fuses when a tube starts to go. Chances are it's only 1 tube that is going but it's a good idea to replace all of them. If it's still blowing fuses then it's either a transformer or the filter caps.
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This is what Jerry from FJA Mods had to say about it:

"Your amp has 5 more fuses inside. My guess is you blew the 2 amp fuse inside. You said a 5V fuse, you meant 5A right? The fuse on the back of your amp should be 5A slow blow. A shorted power tube caused the fuse to blow. You’ll need new power tubes and a new fuse. There could be other damage, but most times it’s just a blown fuse. I doubt his having the amp set wrong really caused the problem, but it is possible that it contributed to the failure. Hard to say and nothing anyone can answer for sure. You should always run the impedance of the amp and the speaker matched correctly. Many folks online will say a mismatch one way or the other is OK, but that is absolutely not true.

Jerry Pinnelli"

So I guess I'm gonna need some power tubes and fuses...