Marshall amp random bursts of static

ido1957

ido1957

9K Gold Member
So I was playing tonight for 2 1/2 hours and I got 3 random 3-7 second bursts of static spread out over that time. Fairly loud static. I looked at the power tubes once as it was happening and they all looked ok - just a yellow/orange glow on the bottom. Couldn't see the preamp tubes from the top. My first impression was tubes (this has happened the past three or four times I used the amp) but I wonder if it could be radio interference. The reason I say that is that I moved it a while back and was getting radio through the amp occasionally. I don't get radio voices anymore but maybe it's some kind of interference. Maybe it's tubes but it doesn't seem to be getting worse as in dying completely or even more often. I'm not gigging so I'm waiting for it to die but it's not. Thoughts anyone?
 
could be tubes ..... could be static ..... could also be bad solder joints ...... I've seen that cause bursts of static.
Which Marshall is it?
 
Greg_L said:
And wouldn't a tube amp picking up radio mean something has gone horribly wrong?
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I hope not! I used to get radio reception faintly coming through my old tube amp from time to time. Of course that was before it stopped working entirely....maybe I should have seen that as a sign?
 
heatmiser said:
I hope not! I used to get radio reception faintly coming through my old tube amp from time to time. Of course that was before it stopped working entirely....maybe I should have seen that as a sign?
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Lol. I don't know, I just seem to notice radio pickup more on SS amps, and have never noticed it on quality tube amps.
 
JCM900. I ruled out the cables and guitar so it's probably some solder joint or tube. Guess I need to get it to the shop. Just had it there a couple years ago for static but much less. They replaced two power tubes and broke/replaced a preamp socket... I could always trade it in on a JVM210 that's sitting in Long and McQuade's. I could probably get a couple hundred on trade. I've got a bonus coming but was going to spend it on my truck payments...decisions decisions...
 
Greg_L said:
And wouldn't a tube amp picking up radio mean something has gone horribly wrong?
Click to expand...
meh .... depends on the signal strength and quality of the radio broadcast.
If a station is close by or has lousy freq control any amp might pick it up.
CBs used to be bad about that 'cause they were cheap crap that spewed noise all over the adjoining bands and the transmitter might drive right by you.
Now no one uses CBs much so you don't hear it as much.
 
Lt. Bob said:
meh .... depends on the signal strength and quality of the radio broadcast.
If a station is close by or has lousy freq control any amp might pick it up.
CBs used to be bad about that 'cause they were cheap crap that spewed noise all over the adjoining bands and the transmitter might drive right by you.
Now no one uses CBs much so you don't hear it as much.
Click to expand...

I have an old Acoustic (the brand, not the style) SS amp that only seems to pick up Spanish radio stations.
 
Quiet at work so I snuck out for a couple of hours and brought my amp to Long and McQuade for servicing. They usually only do warranty work because work piles up so fast, but they said they would do it as I bought it there/had it repaired there before and it was probably a quick tube replacement (let's hope). I saw the JVM210 there but my conscience told me it was a better idea to make a couple of truck payments and get that paid off faster. My wife needs a new vehicle soon anyway. I bought this JCM900 probably 1988 and never needed tubes for years. This amp seems to chew through tubes pretty fast - every couple years - since about 2000. It's been to two different shops with different bias settings - the last shop lowered it to prevent tube burnout when I took it there 6 years back...
 
I've read stories about those early 900s coming with the wrong power tubes from the factory. Then, out of simple habit people tend to keep replacing them with the same kind when in reality they should have a different type altogether. For example, they come with EL34s when they're actually set up for 5881's, or something like that. Maybe it was vice versa. But whatever, I've read that a lot of about 900's. It all got sorted out finally by 1994 or something like that. Check into it.
 
Wow - ready same day with 3 new pre amp tubes for $85. Gave it a quick workout and it sounds okay - actually a little more bottom end if anything. I have to really give it some playing time tomorrow...(kid is studying).
 
I thought the sound always in your fingers...Not really the equipment... maybe wash your hands and trim your fingernails?
 
So I fired up the amp tonight for a longer workout and after half an hour....still have the static. It's even worse than it was before. Static and hum combined. So it wasn't the preamp tubes causing it. It happened with the cord disconnected, so it's definitely the amp somewhere. The only thing that stops it is turning on standby (or completely off). So I'm going to take it back to the shop and get them to look at it a little closer/longer. I think it happens after it warms up a bit. #$%^&
 
ido1957 said:
So I fired up the amp tonight for a longer workout and after half an hour....still have the static. It's even worse than it was before. Static and hum combined. So it wasn't the preamp tubes causing it. It happened with the cord disconnected, so it's definitely the amp somewhere. The only thing that stops it is turning on standby (or completely off). So I'm going to take it back to the shop and get them to look at it a little closer/longer. I think it happens after it warms up a bit. #$%^&
Click to expand...
yeah ..... maybe a different shop although you'll prolly want them to put your old tubes back and get some of that money back.
Bursts of static are NOT gonna be 3 preamp tubes. IF it's a tube it's gonna be a single tube. 3 tubes can't suddenly decide to glitch at the same time to cause static and then quit.
I lean towards a bad solder joint somewhere but ya' know ..... you might try hitting those pots with some DeOxit ..... I have seen dirty pots do that ..... if it's set right at a dirty spot it can go from conducting to not conducting acnd back again.
 
A couple of things to try before I take it in:
- disconnect the Roland GP8 and plug direct into the amp input. The Roland goes into the input not the effects loop.
- move the amp into another part of the room to see if it could be radio interference.
- Turn it on and don't plug anything in to see if it happens.
Might take an hour to test this all out as it's intermittent doesn't happen right away.

Planning on working from home tomorrow to avoid the impending snowstorm. Maybe I can try a few things out then....
 
Ok - a bit of good news.... I played for 2 hours straight without the GP8 effects rack. No buzz, no static, no hum, no volume drop. I sure missed the delay, chourus, compression and overdrive though.

The GP8 mono output normally goes straight into the guitar input on the Marshall. There is an effect loop but I prefer the sound in the front.

Ever heard of an input overload? Faulty amp input? Maybe it's a bad chip/IC/battery in the GP8 - it is pretty darn old maybe 1988 so 25 years old.

I still have a few things I need to test:
- send the GP8 through a different (SS amp) to see if it does it.
- it may be a fluke, I need to play the Marshall a few more hours before I'm convinced it works.
- find a different pedal to test through the front input. Mike's compressor pedal is probably sufficient for this test.

I would like to try a boss gt-100 if a new pedal is what I need.
 
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