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GMC Forum _ GEAR & PRODUCTION _ Amp Screeching Problem, New Tubes
Posted by: JVM May 7 2010, 11:30 PM
Hey GMC,
Recently my amp, a Mesa f-30 began having problems for the first time since I've owned it. Luckily I have a backup and I've been okay without it. I ordered a new set of tubes from Eurotubes (excited to try the JJs!) after a fair amount of reading which suggested it was probably a tube problem. I got an ECC81 for V1 by their suggestion, as I said I wanted a little more headroom on the clean channel and wouldn't mind having a little less gain on the second channel. Otherwise the standard kit they have.
Anyway, the point of this post is twofold: to share the news of my new tubes, which I have never changed before (maybe get a little assistance in the changing) and to describe the problem so that if the tubes are not the solution, we can figure it out.
The amp likes to make a really loud screeching sound at random times after turning the amp on, nothing seems to change it. Reverb off or on, volume high or low, FX send/return levels adjusted, whatever. Also the other day at band practice the amp didn't screech but instead just sounded farty and dead. Earlier today I took the tubes out, put them back in and played for a few minutes and then the screeching again. It sounded as normal for those few minutes though. Also one tube seems to be glowing a bit brighter than the others. Sounds like a tube problem eh?
One other thing. I really like the F-30, but I have plans to buy a matching probably 2x12 cab from mesa, take the speaker (V30) out of the combo and use the combo as a "head" on top of the cab. I'm pretty sure this will work, right? I hope to get a little more air moving, maybe mismatched speakers for a fuller tone (again, I don't know much about this stuff) and plus the whole rig will look bigger without me having to buy a new head. How's that sound?
Thanks.
Posted by: jstcrsn May 7 2010, 11:48 PM
Recently my amp, a Mesa f-30 began having problems for the first time since I've owned it. Luckily I have a backup and I've been okay without it. I ordered a new set of tubes from Eurotubes (excited to try the JJs!) after a fair amount of reading which suggested it was probably a tube problem. I got an ECC81 for V1 by their suggestion, as I said I wanted a little more headroom on the clean channel and wouldn't mind having a little less gain on the second channel. Otherwise the standard kit they have.
Anyway, the point of this post is twofold: to share the news of my new tubes, which I have never changed before (maybe get a little assistance in the changing) and to describe the problem so that if the tubes are not the solution, we can figure it out.
The amp likes to make a really loud screeching sound at random times after turning the amp on, nothing seems to change it. Reverb off or on, volume high or low, FX send/return levels adjusted, whatever. Also the other day at band practice the amp didn't screech but instead just sounded farty and dead. Earlier today I took the tubes out, put them back in and played for a few minutes and then the screeching again. It sounded as normal for those few minutes though. Also one tube seems to be glowing a bit brighter than the others. Sounds like a tube problem eh?
One other thing. I really like the F-30, but I have plans to buy a matching probably 2x12 cab from mesa, take the speaker (V30) out of the combo and use the combo as a "head" on top of the cab. I'm pretty sure this will work, right? I hope to get a little more air moving, maybe mismatched speakers for a fuller tone (again, I don't know much about this stuff) and plus the whole rig will look bigger without me having to buy a new head. How's that sound?
Thanks.
fisrt, turn the amp on-then unpluge it,this alows the stored voltage in the tubes to disapate-Take the amp ouy of the head- carefully -plug it back in - wiggle the tubes on at a time to see if you have a loose connection, i. If you find a particular problem- Start from the top and switch tubes ,to find if it is a defective tube prong or not.Even new tubes can have defective prongs ,if this does not work -the rest is out of my league
hope this helps
Posted by: JVM May 8 2010, 12:22 AM
I was tapping the tubes with a chopstick earlier, one of them made a popping noise when tapped, the other didn't. Pretty sure these are the El84s, I don't see any other tubes. I assume they're behind all the metal housing I see back there. Which is about the only thing making me nervous about the retube, taking parts out of the amp 
Is this easy?
Posted by: MickeM May 8 2010, 12:49 AM
Since this is frequet mantenance they didn't make it rocket science. Yes it's easy. I don't know your model though but still, the general idea must be the same.
EL84's, if that's what you have, sit with thin pins and usually a spring or cap on the top to keep them in place. Removing it is like when the nurse taking a blood sample switch tubes. Be careful not to use too much force or you break the tip.
Spray the pins of the new tubes with electric spray, jack em in and out a few times to lubricate and make perfect contact for the new tubes. Especially important for the smaller tubes with thin pins that can point in any direction.
Be careful not to bend the pins when you try to mount them. That's the only cons of EL84, their weak spot.
Use gloves or a cloth to not put grease from your fingers on the tubes.
Change tubes is a thing you can do for sure. Just take it slow and easy if you're unsure. Never use force, that's when pins and such break.
On and check on how to bias, or are all Mesas self biasing?
Posted by: jstcrsn May 8 2010, 12:55 AM
Is this easy?it is -sort of
there are screws all around the out side of the head. top -bottom and sides , then the guts will just slide out of the head through the back, please make sure it is unplug then go through the steps of previuos post , switch the tubes and then you will know if it is the tube or the socket. If it is the tubes -easy replace- if the same socket makes the noise -you will need some proffessional help
Posted by: JVM May 8 2010, 01:02 AM
Thanks guys. Micke, I'm pretty sure all mesa's are self biasing, I know the f-30 is at least. It does have EL84's. Would spraying the old tubes with electronics spray work to clean out the sockets? And then some on the new ones for good measure? I just don't want to risk bending the pins on the new tubes if I could do it with the old ones. But I did remove and put the old ones back in earlier, it's not too hard so I don't think I'll have problems.
By the way, it is a combo, not a head. Should work about the same way though right? As far as getting in there to get at the preamp tubes.
Posted by: jstcrsn May 8 2010, 01:13 AM
By the way, it is a combo, not a head. Should work about the same way though right? As far as getting in there to get at the preamp tubes.
yes , but you might need to remove the wire to the speakers
Posted by: JVM May 8 2010, 01:27 AM
Okay, that would be very easy. It's just a 1/4" jack into the output.
Speaking of speakers, what do you guys think of my cabinet+combo-as-a-head idea? Another plus I can think of is it would give me a nice space to store things where the speaker used to be. I probably won't do this for some time yet, but I wonder what speaker would be best with the V30, if not another V30. And then there's the different back configurations, closed, open, 3/4...
Posted by: jstcrsn May 8 2010, 01:55 AM
Speaking of speakers, what do you guys think of my cabinet+combo-as-a-head idea? Another plus I can think of is it would give me a nice space to store things where the speaker used to be. I probably won't do this for some time yet, but I wonder what speaker would be best with the V30, if not another V30. And then there's the different back configurations, closed, open, 3/4...
always IMHO get a closed back. Open back cabs don't get the low end. See if you can try out both at a music store and i think you will notice the difference.
I think after rereading your post your problem is the combo is problbly open back -if so take your combo to the store and see if you can hook up a closed back for comparrison . sorry for the redudancy
Posted by: Ivan Milenkovic May 10 2010, 03:05 AM
Speaking of speakers, what do you guys think of my cabinet+combo-as-a-head idea? Another plus I can think of is it would give me a nice space to store things where the speaker used to be. I probably won't do this for some time yet, but I wonder what speaker would be best with the V30, if not another V30. And then there's the different back configurations, closed, open, 3/4...
I think it's a very good idea, you'll have a more bigger sound to work with on stage or in studio. For home use, it doesn't have too much sense - one speaker will create enough bass.
What speaker is a bit of a wide topic, there are so many out there, and it is highly subjective. Experimenting is the key (often it is not possible, but it's the ideal way of getting to know them). I think putting two different speakers is a good idea, because you can instantly compare them in the same box.
I like closed back, they have more bass and the sound is focused towards front. You can try some cabs and see what you like.
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