FiliphSlim

Hello, I'm new to this forum and this is my first post.

The reason I'm posting is this;

I bought a Marshall Valvestate S80, 40 watts (model 8240), from a friend today. I got it pretty cheap because we knew that it wasn't in it's best condition.

Anyways, directly when I turn the amp on, I get a pretty loud buzz/hum or whatever you could call it. It's there even when all the knobs are turned off and I tried all the buttons but it won't go away.

Well, that's not really the big problem. This is really wierd and I don't know really how to explain it. The thing is, when I start to play, I get this really wierd sound, almost as an effect was still on, like flanger/chorus or maybe a reverb, even though all the effects are turned off. I get this on both channels, but I believe it's worst on the gain one. I can turn it up pretty loud and still play as usual but it sounds like crap, not like a speaker has been blown, but just that freaking wierd, bad sounding effect.

My friend telled me about how it first got there. I wasn't there when it happend so I'm not entirely sure but this is what he said happened;

He just got it, but I think it was from the 90's or something, turned it on and it played really good, then he put on some reverb. But he was rehearsing with his band so I guess he took the volume all the way up. Then he took his (dist?)pedal between the amp and the guitar but when he turned it on he heard some kind of sound/pop/boom, I don't know. And after that, it sounded really wierd, kind of like it does now, I guess. But then when he switched to the clean channel it was all good.

The next day when he turned it on though, it sounded just like it did when the accident had happened the day before!

I'm sorry for this wall of text, but does anyone of you have an idea what could have happend and if there's any way to make it work good again?

Thank you, hoping to get some kind of replys, hehe.

Peace

stryker59

well firstly...welcome to the forum!
as for your amp, pops and booms are never good things! it seems like something has fried on the circuit board, i would take it to a tech to have it looked at....

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coldsteal2

if its that old i think it probably needs a new
preamp tube for starters

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FiliphSlim

It's from the early 90's.. -93 i believe....

bossboy2

Ditto...check the preamp tube first. They do all kinds of wierd stuff when they go bad.

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FiliphSlim

Is there any easy way to "test" the preamp tube by myself or will a tech have to do it?

amplifier

Sounds like it's gone microphonic. Unless you've got the gear to test valves the only way to really test it is to buy a new one and see if it fixes the problem. Don't waste your money on a tech it's easy. There should be 4 screws on the top holding the chasis up. Hold your hand on the bottom when you unscrew them so the chasis doesn't drop and get damaged. The tube should be near the input jack. I'm not sure if the older ones have a retainer holding the tube in but if it does move it to the side and cafefully and firmly start making small circular motions till the tube comes out. Use the same technique to put the new one in and put your chasis back on. Good luck!

Stretchy

Hey there Amplifier... I love to learn new things and you seem to know way more than me. So here it goes... what does it means when I tube goes "microphonoc" ?

Thanks!

amplifier

Sure thing buddy ol' pal. When a tube goes microphonic you can get bad feedback (edit even with your guitar turned down)or certain frequencies will continue to ring out, like when FiliphSlim mentioned it sounds like it has a reverb effect on. You can also see if it's going microphonic by tapping the tube w/the eraser end of the pencil slightly. You'll hear it through the speakers but if it continues to ring it's going bad.

FiliphSlim

Ok, sure, it could try that. Maybe I forgot to mention that this is an solid state amp, but you got that right?

Did the same thing on my Fender 65 Deluxe Reverb...

Stretchy

Thanks pal! Know something new today!

Great forum, great members!

amplifier

Your Marshall is a hybrid, it's got a 12ax7 in the preamp.

FiliphSlim

But what should I remove? When I look into it from the back, there is one big metal box right where the panel is on the other side, and there is on the the right "wall"/side of the amp....

amplifier

I'll just have to quote myself here:

Stretchy

Also, on the Valvestate 40 watts (I have a 8040... very similar to the 8240), you'll see a small metal retainer, push it to the right (facing the back on the amp) then gently twist left and right while pulling to get the tube out.

I've replace my original Marshall amp with a JJ.... sound very nice!

FiliphSlim

Well, now the tube is out, just have to replace it. I found one tube in my room, new & sealed of course, but I don't know if it would fit.

It's a "groove series, electron tube" On the tube it says GT12AX7C.....

It also says "ECC 83" on both this one, and the old tube which I took out of the amp

Would it work to just put that one where the old one was or would I blow it up?


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EDIT: I tried and it worked, I believe that the sound is improved but with that buzz it's hard to even hear it.

I also noticed that the buzz is in the key of G (?!) so when I play in G it sounds okay, hehe...

But what could be the cause of this buzz? Broken/burnt ground, bad transistor or some cooked component?

I don't know..

Thank you for your help this far, it's been awesome, but now I need help to solve this buzz problem....

stock_hippie

wow

FiliphSlim

?

sorry for being a noob, but this is the first time I've tried to fix an amp, I'm usually a player...

FiliphSlim

I also believe there's also a huge loss of volume. I haven't heard a new, fully working one, but with this amp, I can sit right in front of it without being bothered because it's loud when everything is on 10...

FiliphSlim

I heard someone say that it probably was a failed power supply capacitor.

If so, is that anything that I can fix by myself, if so what would it cost? Or should I just take it to a tech?

coldsteal2

you can buy a tube tester, im thinking about getting one
myself

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FiliphSlim

What would I need a tube tester for? I've got a new, fully working tube...

amplifier

I think what he meant to say is, your screwed! HA! j/k I think it's time for a tech sir FiliphSlim. Good day.