Problem with Marshall Valvestate

[therooster]

Hi everyone, I hope you can help me with this...

I have a Valvestate 8080 that developed a problem yesterday...



It had been sitting in the same room for a year and yesterday I moved it to another room. When I plugged it in and switched it on, this loud background noise/static appeared. I can still hear an instrument being played through it, but the sound is really tinny and faint.

I have the effect knob set to dry. In the clean channel, the noise is present whether the guitar is plugged in or not. It becomes higher-pitched when an instrument is plugged in (but nothing like a whistle, rather like TV static). Turning the treble and middle knobs down change the noise significantly (it alleviates the problem). Turning the bass knob down doesn't do much.

In the boost channel, the noise is present only when an instrument is plugged in. The sound of the guitar sounds even fainter than in the clean channel.

Now, I'm a complete noobie when it comes to these things... I think these amps have an ECC83 pre-amp valve in them for the boost channel, but I thought that even if the valve dies, it shouldn't affect the amp operation like that. Or is this a sign that a new valve may be needed? I never changed it since I bought this amp in the early 90s.

Any help and suggestion would be much appreciated, but please remember that I'm no expert about components etc...

Thanks a lot

[sumgai]

rooster,

Hi, and to the NutzHouse!

First question: what was your amp doing in the other room for a year and a half.... sitting unused? getting played every day?

Next question: was the other room part and parcel of the house.... was it heated? Or was it in a closed off storage area?

Regardless, my money says you have a broken input jack, or at the least, it has come unglued (technical term) from the circuit board. Your description says to me that it's at the very input of the amp, and these jacks are not known for any kind of longevity.

Beyond that, I wouldn't ordinarily suspect the tube, but you don't lose anything by swapping it out for a fresh one, just for test purposes. I doubt this is the culprit, but like I said, it's the quickest and easist thing you can do to eliminate one more possibility.

HTH




sumgai

[therooster]

Thanks for the kind reply and for welcoming me to the forum!

The amp was sitting in a bedroom and getting played maybe once a month or less... so yeah, it wasn't seeing much use at all. The room was heated etc and just upstairs from the current location of the amp.

Is it possible to check if the input jack is broken? Is that something visible to the naked eye?

Thanks again.

[sumgai]

rooster,

Getting to your question in a more logical order....

What happens if you take the amp back upstairs? Sometimes location is all that's causing noise problems like this, and solving that kind of issue is another troubleshooting process entirely.

If that doesn't help, then swap the tube. Still no workie? Then it's time for some good old-fashioned visual inspection.

Plug in a cord and see how it feels. Usually some piece of plastic has broken off, and you'll feel a difference between that, and a good jack. But that's only half the battle. Sometimes the jack has come unsoldered from the circuit board. The jack will "feel" the same when you plug in a cable, of course, but now you get to do the remove-chassis bit.

Additionally, it sometimes happens, though not as often, that the contact on the jack's inside can become loose and/or bent up out of the proper position, thus making good contact with the cord an intermittent thing.

Removing the chassis from the cabinet is straightforward - four screws on the top, and unplug the speaker. (You may need to do something about the power cord - different models handled the cord in different ways, but they're all easy to deal with.) Eyeball the jack carefully, and 8 times out of 10, you'll see the issue. Wiggle the jack a little - if it's even a tiny bit loose, that's a sure sign of one or more bad solder joints.

HTH



sumgai

[therooster]

Hi, no, the problem is not location-specific. The amp just sounds busted wherever I put it.

I can't feel anything odd with the jack... As soon as I have some time (probably next week) I will do as you suggest and check out the input carefully. If in the meantime you have any other ideas, please do let me kow.

Thanks for your help.

[sumgai]

roos,

You didn't say if you've already done so, but the only "other" idea I have is to swap the tube, before you take anything apart. If that doesn't work, then we'll get down to brass tacks.

Just be aware that remote troubleshooting like this is time intensive, and not amenable to my seeing what you're seeing. (Unless photos become involved.) I can only give you benefit of my years of experience in both the technical and engineering side of things, but that all depends on your descriptions. And for all that, there are no guarantees that we'll hit the problem right on target - you may still end up seeking out a valid repair tech (preferably one that is trustworthy).

But let's give it the ol' college try, shall we? ;D




sumgai

[razbo]

Hmm, nothing since that last post date. I'm a little worried 'roo might have fried himself going inside his amp. ;D


...sigh