Problem with Marshall Valvestate

[msk011]

Hi Folks,

My brother has an older (probably early 90s??) Marshall valvestate 100 watt 1x12 amp. I was over there watching the Lions get waxed by the Cardinals yesterday and saw it collecting dust in a corner. It has this problem where you can play it for a few minutes normally and then something happens and the volume just goes away. I don't think it goes completly, just gets really quiet. I know he tried replacing the tube a couple times with no luck. I decided I want to get it fixed if it won't be too much money. Can anyone comment on possible causes or if these amps are know for this before I take it to the repair man? Just wana make sure it's not somthing simple before I pay.

Thanks,

Mike.

[jjasilli]

This may not be very helpful, but I had a friend with the same problem with that amp. We replaced the tube and the problem went away, but then returned again. (The problem was resolved, for me only, when my friend moved away.)

[John Phillips]

It's very likely that one of the high-power resistors on the back circuit board has desoldered itself and is making intermittent contact. This - and filter caps coming loose, which causes loud hum and/or farty 'blown speaker' noises when it isn't - are the most common faults on Valvestates by far. It's easy to fix - remove the resistor, clean up the solder joints and the component legs, re-insert the resistor, bend the tip of the leg down firmly onto the board to lock it into place (which was never done originally), and resolder. It may be worth doing all the resistors (there are about five of them, depending on the model) and the two large filter caps at the same time even if not all of them are showing signs of problems... it will save you ever needing to do it again.

I would say that at least three-quarters of the faults I've ever had to fix on first and second series Valvestates are this.

[msk011]

Originally Posted by John Phillips

It's very likely that one of the high-power resistors on the back circuit board has desoldered itself and is making intermittent contact. This - and filter caps coming loose, which causes loud hum and/or farty 'blown speaker' noises when it isn't - are the most common faults on Valvestates by far. It's easy to fix - remove the resistor, clean up the solder joints and the component legs, re-insert the resistor, bend the tip of the leg down firmly onto the board to lock it into place (which was never done originally), and resolder. It may be worth doing all the resistors (there are about five of them, depending on the model) and the two large filter caps at the same time even if not all of them are showing signs of problems... it will save you ever needing to do it again.

I would say that at least three-quarters of the faults I've ever had to fix on first and second series Valvestates are this.

Thanks John, I'm handy with a soldering iron so I may take a crack at this problem. I'm assuming it will be fairly obvious if the resistor is the problem?

Mike.

[msk011]

Originally Posted by jjasilli

This may not be very helpful, but I had a friend with the same problem with that amp. We replaced the tube and the problem went away, but then returned again. (The problem was resolved, for me only, when my friend moved away.)

Maybe I can get my bro to move away

[John Phillips]

You'll probably find that if you run the amp with the chassis open, you can make the problem come and go by poking one of the resistors - it may even clearly move about. They're the large white block components on the rear board, but if you're handy with an iron you probably didn't need me to tell you that .

FWIW, these aren't bad amps really, and once simple problems like this are taken care of they're quite reliable and IMO sound OK... though not to everyone's taste.

The ones with the Celestion speakers sound better than the ones with the Eminences ('Marshall Gold'), and in both cases you should consider cutting the nasty little push-connectors off and soldering the wires to the speaker. (If it's an Eminence, it may be worth soldering the crimps where the cone braids are held to the tag, too - they sometimes fail there.) You can still get the chassis out without undoing the speaker if you lay the amp face down and rest the chassis across the back of it at an angle.

You may realise that I have worked on 'quite' a few of these amps .

[msk011]

Originally Posted by John Phillips

You'll probably find that if you run the amp with the chassis open, you can make the problem come and go by poking one of the resistors - it may even clearly move about. They're the large white block components on the rear board, but if you're handy with an iron you probably didn't need me to tell you that .

FWIW, these aren't bad amps really, and once simple problems like this are taken care of they're quite reliable and IMO sound OK... though not to everyone's taste.

The ones with the Celestion speakers sound better than the ones with the Eminences ('Marshall Gold'), and in both cases you should consider cutting the nasty little push-connectors off and soldering the wires to the speaker. (If it's an Eminence, it may be worth soldering the crimps where the cone braids are held to the tag, too - they sometimes fail there.) You can still get the chassis out without undoing the speaker if you lay the amp face down and rest the chassis across the back of it at an angle.

You may realise that I have worked on 'quite' a few of these amps .

Thanks again John, I PMed a message to you a minute ago asking for some book recomendations.


Thanks again.

Mike.

[Backstage Kent]

Most Valvestates (and indeed, the VS100 is one of them) route the speaker out ground through a switching contact on the headphone jack, which I've seen A. poorly soldered B. oxidized C. both, resulting in exactly the symptom you describe. A good shot of DeOxit into the headphone jack, followed by multiple insertions/removals of a 1/4" plug, may well at least attenuate the problem. If it does, it's worthwhile to replace the jack, as cleaning the contacts tends to be a short term fix in my experience.

[HipKitty]

Originally Posted by John Phillips

It's very likely that one of the high-power resistors on the back circuit board has desoldered itself and is making intermittent contact. This - and filter caps coming loose, which causes loud hum and/or farty 'blown speaker' noises when it isn't - are the most common faults on Valvestates by far. It's easy to fix - remove the resistor, clean up the solder joints and the component legs, re-insert the resistor, bend the tip of the leg down firmly onto the board to lock it into place (which was never done originally), and resolder. It may be worth doing all the resistors (there are about five of them, depending on the model) and the two large filter caps at the same time even if not all of them are showing signs of problems... it will save you ever needing to do it again.

I would say that at least three-quarters of the faults I've ever had to fix on first and second series Valvestates are this.

I have to concur with John....also look for any bad solder points anywhere within the amp... bad solder points can present the same problem of intermittent function ability.

[Backstage Kent]

Interesting--I've worked on tons of Valvestates and seen very few with power resistor solder issues--the jack problem is much more common here. Go figure. Of course, anytime I pull one of these boards I resolder all the large pin components and the multipin cable connectors just to be sure I don't have to see them again.

[John Phillips]

It is funny how repairs seem to go differently in different places! I have seen the bad headphone jack issue too, but only a handful of times. It may depend on the pattern of use - if they've been run hard the resistors are much more likely to overheat and vibrate themselves free, and the headphone jack contacts will even almost spot-weld themselves under heavy current (it's a poor design anyway, there is no more than a single line of contact along the edge of the switch piece) - but if they've been used lightly the jack is more likely to corrode first...

The other weird one is when you get 'the week of blown speakers' and the 'the week of filter cap jobs' and the 'the week of...' when you would expect the type of job to be more evenly distributed.

[Backstage Kent]

Originally Posted by John Phillips

It is funny how repairs seem to go differently in different places! I have seen the bad headphone jack issue too, but only a handful of times. It may depend on the pattern of use - if they've been run hard the resistors are much more likely to overheat and vibrate themselves free, and the headphone jack contacts will even almost spot-weld themselves under heavy current (it's a poor design anyway, there is no more than a single line of contact along the edge of the switch piece) - but if they've been used lightly the jack is more likely to corrode first...

The other weird one is when you get 'the week of blown speakers' and the 'the week of filter cap jobs' and the 'the week of...' when you would expect the type of job to be more evenly distributed.

I think this is to dissuade us from the notion of an orderly universe.

[msk011]

Originally Posted by Backstage Kent

Most Valvestates (and indeed, the VS100 is one of them) route the speaker out ground through a switching contact on the headphone jack, which I've seen A. poorly soldered B. oxidized C. both, resulting in exactly the symptom you describe. A good shot of DeOxit into the headphone jack, followed by multiple insertions/removals of a 1/4" plug, may well at least attenuate the problem. If it does, it's worthwhile to replace the jack, as cleaning the contacts tends to be a short term fix in my experience.

Thanks BK, that's even easier than what John said!

Mike.

[msk011]

Thanks again for the replies folks.:BEER

Mike.

[dbsub9]

Hi, My VS 8040 has a few issues. the most prominent issue is that I can be in either the clean or drive channel with the volume set low and then I'll experience a loud jump in the volume. The pots also seem to be dirty because most of the knobs make a lot of noise when turned. Could this be a transformer issues. I've found that the drive channel when set at a certain level can be played without the volume problem but it sounds a bit "weak". Can anyone help?

Thank you in advance!
Dan

P.S. I lent this amp out and it sat for quite some time without being powered on and collecting dust.