Bare Knuckle Pickups Forum
Forum Ringside => Guitars, Amps and Effects => Topic started by: indysmith on November 06, 2006, 01:04:16 PM
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okay - i got new valves for the jcm800 - whacked em in to give them a test - switched amp on on standby, left for 5 mins, turned off standby, played for about 10 seconds, sounded great, and then all sound just cut out completely.
I hadn't rebaised for these valves (i don't have a clue how, and i don't know anyone who does), but i thought it'd be the valves that would be damaged if i didn't rebias it properly and it was running hot. I've changed back to the old valves and still no sound at all. have i buggered the transformers or something? this sucks so hard. it's gonna cost me a bomb to fix isn't it?
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All the transformers and valves and everything look the same - there's nothing visibly blown up or anything. ARGH why do i break everything!?
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deep breath, calm down
have you checked fuses?
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deep breath, calm down
have you checked fuses?
Thanks man; so how do i check fuses - where are they and why would they break?
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Should be two fuse holders on the back - one for the mains input and one for the power valve circuit. They'll be in glass tubes so you can see if they've broken or not.
A faulty valve would blow the power valve circuit fuse, which I suspect is your problem. A fault elsewhere is more likely to blow the mains fuse.
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okay the fuse that isn't the mains fuse (i think) has blown (i think) it's got some black burnt looking marks on the inside of the glass (which is intact) that the other fuse doesn't. I'll post some pics ina second - but they'll be shitee quality as i can't find the real camera
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(http://img294.imageshack.us/my.php?image=blownfuseyn9.jpg)
I really apolagize for the rubbish quality of the pictures.
Does this mean that i just need to send the valves back and replace the fuse?
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well the fuse def. looks blown.
Maybe replace fuse and put orig. tubes back in and test.
Probably a tube blew it but why is another matter.
Bit hard to diagnose on pc :)
Are they diff. tubes that could have been needing a bias?
Try replacing fuse and putting orig. tubes back I would say.
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well the fuse def. looks blown.
Maybe replace fuse and put orig. tubes back in and test.
Probably a tube blew it but why is another matter.
Bit hard to diagnose on pc :)
Are they diff. tubes that could have been needing a bias?
Try replacing fuse and putting orig. tubes back I would say.
yeah they would probably be needing a bias - i'm off to town to get another 500mA fuse - thanks for your quick and useful help guys. Be prepared for a thread asking how to bias a jcm800 4104 :P
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For ANYONE buying a valve amp, you can save yourself a lot of trouble by adding the following to your library:
http://www.amazon.com/Tube-Amp-Book-Aspen-Pittman/dp/0879307676/sr=1-1/qid=1162822065/ref=sr_1_1/102-0602884-5084945?ie=UTF8&s=books
http://www.amazon.com/How-Service-Your-Tube-Amp/dp/0962817007/sr=1-2/qid=1162822065/ref=sr_1_2/102-0602884-5084945?ie=UTF8&s=books
http://www.amazon.com/History-Marshall-Guitar-Amplifiers-1962-1992/dp/0793525098/sr=1-1/qid=1162822552/ref=pd_bbs_sr_1/102-0602884-5084945?ie=UTF8&s=books
This will solve a lot of panicked posting!!
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For ANYONE buying a valve amp, you can save yourself a lot of trouble by adding the following to your library:
http://www.amazon.com/Tube-Amp-Book-Aspen-Pittman/dp/0879307676/sr=1-1/qid=1162822065/ref=sr_1_1/102-0602884-5084945?ie=UTF8&s=books
http://www.amazon.com/How-Service-Your-Tube-Amp/dp/0962817007/sr=1-2/qid=1162822065/ref=sr_1_2/102-0602884-5084945?ie=UTF8&s=books
http://www.amazon.com/History-Marshall-Guitar-Amplifiers-1962-1992/dp/0793525098/sr=1-1/qid=1162822552/ref=pd_bbs_sr_1/102-0602884-5084945?ie=UTF8&s=books
This will solve a lot of panicked posting!!
haha thanks Ben - i might just have to look into those.
I went to the hardware store and apparently 500mA fuses are quite hard to come buy - i'm going to have to order one off the internet. Do you guys think the fuse blew because i didn't rebias?
EDIT: bugger, that wasn't as easy as i thought it'd be - i can't find one of the right values and the right size on the internet. I've emailed marshall - i guess i'll have to take it to MK to be sorted.
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Surely a fuse can be sourced here?
http://www.maplin.co.uk/searchtemplate.asp?criteria=500MA%20FUSE
Also, maybe best to let a shop bias your pride and joy. NO disrespect intended but some experience with electronics and some electronic test equiptment is a very good idea to enable bias'ing. This may turn out more costly initially for you, esp. if not used a whole lot thereafter.
Here is a article on bias'ing a JCM 800 (not only way to do it, but will give ya an idea).
http://tone-lizard.com/Biasing.htm
http://tone-lizard.com/Marshall_bias.htm
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Have you checked the valve sockets (where the valves plug in)? That's what caused a similar problem in my old Laney as they're a known weakspot. However, mine smelled of burning really badly when it went and it went black. I think you would have noticed that if it had gone on your Marshall...
If the power tube fuse has blown it usually means a problem with that part of the circuit - could be a bad valve or a blown component of some other description.
I'd replace the fuse (I get mine form Maplins via mail order, or call in if there's a shop near you) and replace the valves like Dakine says. If it blows again, it's likely you've got a non-valve related problem...
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Re: The tone Lizard site.
I like that man's style. I've come up against a few Jedi amp techs in my day, and it's nice to hear someone at least trying to debunk all the surrounding cr@p.
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P.M Bainzy, he is the amp dude in here!
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OY JM
Figured a BKP Fest date/venue yet? ;)
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OY JM
Figured a BKP Fest date/venue yet? ;)
Nah not yet mate. I've been a bit busy sorting out work. I'll have a think once i feel less in limbo and secure!! I did start a new job today and it went well so could be soon. I had a rehearsal yesterday at a studio right on junc 25 of the M25 (easy to find). It's a giant room with P.A and a large old sofa for drinking, plus a drum kit! Does that sound ok? :lol:
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you change damn jobs more than I do gear :lol:
So what ya doing now thats allowing you to abuse the public :wink:
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you change damn jobs more than I do gear :lol:
So what ya doing now thats allowing you to abuse the public :wink:
I'm back doing waste disposal! That dairy job that was promised me by a driving agency turned out to be a non starter. Ffing bullshiteeers, so I blew 'em out and got a job on a roll on roll off, 8 wheel 35 tonne 02 Foden! It's so heavy metal it's sick dude!! I love it and want to go back to work right now! :twisted: :twisted: It's got 8 gears plus another 4 half speeds so 12 in all, a stereo that works too. The people who run the firm are decent and helpful too, unlike the other place. Plus there's a really nice woman in the office with huuuuuuuge tits! :lol:
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Huge engines and big hooters, can' t ask for much more can ya :)
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the HT fuse rarely blows from a misbased output valve - you've more than likely got a bad valve right out the box. get some new fuses, pop the old set back in and take it from there.
I've had bad valves right out the box from all of the main valve dealers in the country - they're all as bad as eachother despite their supposed 'testing' you pay extra for :roll:
:twisted:
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You should take it to a tech and make sure that if there's a reason that fuse blew other than being old that you get it addressed immediately! Fuses seldomly just go for just being old...
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most guitar stores will sell you that fuse, just ask for a "marshall slo-blo fuse" they'll know what you mean.
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most guitar stores will sell you that fuse, just ask for a "marshall slo-blo fuse" they'll know what you mean.
I've ordered a pack of 10 from maplin.
Do you guys reckon i should send the valves back to hotrox then?
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Not yet - I'd wait and see what happens with the new fuse. If your amp is OK with the new fuse and old valves, put the new valves in. If the fuse goes again, then there's a problem with the valves so you should send them back.
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I dont know where in Bucks you are but why not pop into the Marshall factory in Bletchley- they could sort out the bias issues
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I dont know where in Bucks you are but why not pop into the Marshall factory in Bletchley- they could sort out the bias issues
yeah i've already contacted them - i think i may do exactly that :)
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once again guys - just checking; would/could not biasing for new valves blow a fuse?
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Your local music shoppe will sell amp fuses, last time I blew one, it cost me all of 50p to replace!
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ha :P i got 10 for 2.50
Well i've replaced the fuse - and tried with the old valves - worked fine.
Put new valves in, sounds fantastic, works well. maybe it was just an old fuse? :? if it sounds great do i still need to take it alla way to MK for a rebias?i love this amp even more now than ever 8)
EDIT: a quite noticable deep bassy humming noise gets louder as i turn up the master volume - wasn't there before? :? in comparison with the volume of the guitar it barely exists but still. now i'm hearing some short bursts of crackling aswell :? which have just gone away.
I guess it's biased way too hot atm?
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okay, so now the amp has this hum, the crackling is gone, but the sound gets quieter sometimes, and fades in and out. sounds like someone's rolling my guitar's volume back and forth at points. The amp sound AMAZING like actually awesome - MY sound completely. I love nothing more, but the valves are stupidly hot and i'm sure this isn't healthy for them...
For that reason i've switched the old power valves back in, but the hum is still there, and i'm getting a squealing feedback at high volumes, even with my guitar's volume on 0.
I'm sure that this didn't happen before....
bugger
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the feedback is only occuring with the new preamp valves. this whole revalving thing has turned out to be a total disaster- i guess the preamp tubes are at fault...aswell as the power valves?
have i destroyed ALL of my new valves or does it seem likely that they came that way?
i'm actually kind of glad - my amp sounds as it did before all this malarke now with all the old valves back in. phew
i didn't even know that not rebiasing an amp could harm PREAMP valves :?
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to me it sounds like the people who shipped your tubes just didnt take care of them enough.
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Biasing only affects output valves. Preamp valves are self biasing.
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okay well i've emailed hotrox to tell them that the valves arent sounding nice. and they've emailed me back like "what?! that shouldn't happen!", hmmmm.
Well i'm certain that i've played no part in the destruction of the preamp valves, so i'm probably not resposible for the power amp ones either i hope. I'll just have to wait and see how this goes...