Ive got a marshall 8080 valvestate guitar amp, but everytime i put a fuse in and turn the power on it blows the fuse. all the valves have been changed and this didnt solve the problem. would be great if someone could help me out
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Firstly, do not disconnect the speakers from the amp when it is on. Damage is possible.
You have a bad ground somewhere in the hookup. The first suspect would be your guitar-to-amp cord shielding connections at each plug, then, the wiring in your guitar. Try changing each of these to another as a trial, one at a time.
schematic can be found here http://music-electronics-forum.com/t21559/
and on google are heaps of results.
Unfortunately I don't know what the switches are for. But I would begin to check if the channel switch and the switching part (maybe IC2, did't find the datasheet).
Without having the amp on my desk its hard to see the signal flow
I have fixed so many of these amps over the years... Marshall Valvestate series of amps are notorious for dry solder joints developing on the main PCB. If you have the skills(or an old mate that does)Remove the PCB from the chassis and resolder any suspect dry joints and you will fix the problem. Check particularly about any components there the PB has changed colour. This is an indication of heat in that area, and heating and cooling is a major cause dry joints. I am more than happy to answer
any other questions you may have about it, just give me a hoy :) If you
are still unsure, or have problems, then before you give a rating for this advice, please
get back to me and we can try some more things.
Thanks for using FixYa, If you consider the advice I have given you
as sound, a FixYa rating is a great reward for my efforts to help
When I turn on my marshall amplifier its makes this unusual, anoying sound. it sounds like a small motor or a fan going. the sound of the amp is good but its just makes this motor sound when I switch it on. can you help me find the problem.
Hi chagzuki, you are right, but only when the valves are used as outputs, You amp has transistorised outputs, and a single tube used for distortion/gain. You will get a very long life out of this tube also because its supply voltage that is is used in the valvestate preamps is really quite low. Just enough for it to work really, so the tubes life can be expected to be much longer than normal. It is also a preamp tube, not an output tube, so they rarely need changing. If you ever did want to change it(dont bother), it is located on the PCB inside the unit. You have to slide the sleeve off to get at it. Get yourself a JCM800=the best guitar amp ever built(imho), then yo got pure Marshall tone, and output tubes that need changing every 6 months or so. Now go RIFF OUT and dont worry about your valvestates' "valve"
A lot of Amps come with fuses as a safety mechanism so you don't blow the speaker and/or internal components in the case of a power surge etc. Check for a blown fuse. Sometimes they have a fuse holder in the back of the amp and it is labelled "fuse" which cetainly makes it easier to find. Hope this works and helps.
I would go ahead and take it apart, after you unplug it or course. if there is fuse on the back there will be one just off the ac line inside. These amps have an 12ax7 tube in them I beleive ,and large filter capacitors in them where voltage could be stored for a time after you unplug it ,but this is a fairly modern amp with bleeder resistors so it will be safe . you can wait over night to be safe, anyway you won't go touching the large capacitors anyway you are just changing a fuse. look for something like 2 amp or 5 amp in value. replace it with the same value.