Please HELP!!

Presence76 · 02-14-2009, 06:51 AM

I have a Mesa Boogie F30 combo amp. A few months back, I did a full retube with Eurotubes. It made a world of difference (I had owned it 3 years prior to that point). Then, after four months, when I was playing at a small function, my amp made a loud crackling buzz (like it was farting for lack of a better description). I immediately turned it off, waited, then turned it back on, and it was o.k. for a few minutes, then happened again. I then plugged directly in (bypassed my pedalboard) and still encountered the problem. It seemed to happen whenever it was pushed.

I brought it home, and switched out the V2 preamp tube, and it was fine. But-the next day at church, it happened again. Then I replaced my speaker, assuming I had melted the coils, and got an Eminence Governor 75 watt- figuring the extra 15 watts would be protection if I drove it too hard. It was fine for a worship set, then I was playing the same small function, turned up to around 1:00, and it happened again. I tried replacing the V4 tube last night, and it worked ok. I don't think it's the speaker because I ran into my board at home and muted the speaker, and it happened again.

Maybe it was the preamp tube, but I'm wondering if it's something more. Or maybe something is overheating and I should get a fan. When it happens, I turn it off, and the noise stops and doesn't come back for a little bit. I don't know much, so any advice is appreciated.

Thanks!

RubberChipmunk · 02-14-2009, 09:38 AM

How old is the amp? It could be the electrolytic caps. People use them because they're cheap, but they wear out over time and need to be replaced.

Major Tom · 02-14-2009, 11:38 AM

I would first pull all the tubes and stick them back in - that often fixes pin to socket connection problems which can cause symptoms like you have.
After that I would try the tap test - amp powered up, volume up to normal level, and tap the tubes one at a time to see if any of them will make that sound.
Next, I would try swapping out the tubes, one at a time - including the power tubes ( you did not mention trying new power tubes).
If none of the above work, I would try the fist test. Powered up, normal volume, try banging on the amp a bit to see if it might be a bad connection / bad solder joint type issue. don't hit it so hard that you break it, but like you mean it.

If all the above fails, you might want to take it to a tech... If it isn't the user-replaceable tubes, or connection type issue, it could be any component in the amp, like a capacitor or something - sometimes a component will work ok until it gets hot, or up to a certain threshold of voltage or current, which is below its original rating. Amps and devices use electrolytic caps not because they are cheap (?!), but because those are the only type that are made (that I know of) for higher capacitance values needed for power supply filtering. Like tubes, electrolytics at some point will "wear out", not as much from use, but age; modern ones can last decades. Actually it is better for them to be used occasionally, than to sit in an unused amp for years. Of course, like any other electronic component, they can fail or "partially fail" for no apparent reason at any time.

Presence76 · 02-14-2009, 01:34 PM

Hey, thanks for the replies! I did try tapping on/changing all the tubes. I've done everything except bang on it, which I will try soon. I did pull out the "guts" and noticed there is a brown substance on the electrolytic convertors. After reading the tube amp help here, it is making me think it may be those. Then my question is, if I can solder, is it something I could replace? Also, if it is those, would that be what made the noise? btw-the amp is about 5 or 6 years old...

RubberChipmunk · 02-14-2009, 02:14 PM

Quote:

Originally Posted by Presence76

Hey, thanks for the replies! I did try tapping on/changing all the tubes. I've done everything except bang on it, which I will try soon. I did pull out the "guts" and noticed there is a brown substance on the electrolytic convertors. After reading the tube amp help here, it is making me think it may be those. Then my question is, if I can solder, is it something I could replace? Also, if it is those, would that be what made the noise? btw-the amp is about 5 or 6 years old...

Do you mean the electrolytic capacitors? I'm not familiar with an electrolytic converter. If that is what you mean, yes, you can replace it yourself, but you'll need to be incredibly careful, as the caps carry lethal charges in them which you will need to discharge from ALL of the caps before you do any soldering work on the amp.

Major Tom: I've read in a few places that they are mainly used in guitar amps due to the generally inexpensive price of them compared to other capacitors.

Major Tom · 02-14-2009, 02:17 PM

Quote:

Originally Posted by Presence76

Hey, thanks for the replies! I did try tapping on/changing all the tubes. I've done everything except bang on it, which I will try soon. I did pull out the "guts" and noticed there is a brown substance on the electrolytic convertors. After reading the tube amp help here, it is making me think it may be those. Then my question is, if I can solder, is it something I could replace? Also, if it is those, would that be what made the noise? btw-the amp is about 5 or 6 years old...

Brown substance - Amp mfr's often use an adhesive / caulk type compound on the large components like electrolytic caps to keep them glued down to the pc board, and often if they are in a row, glued to each other, to prevent them from coming loose if the amp gets a little abuse. It would have a similar appearance, and may even be, a form of hot glue. Usually that stuff is clear or milky, but what Mesa used could be brown .If it is on all of them, underneath, and in between, I would say that is what it is. If it looks like something actually leaked out of a single cap (the odds would be against multiple caps going bad), that might be an indication that it needs replaced.

Pic?

Quote:

Major Tom: I've read in a few places that they are mainly used in guitar amps due to the generally inexpensive price of them compared to other capacitors.

Try to find any other type of capacitor that is 22 or 44 uf like what is commonly used in a tube amp, much less, the 1000, 5000, 10000 uf caps used in computer grade power supplies. I've never seen any. Be careful what you read on the net, it is a great source of information and yet an equally great source of disinformation.

Quote:

Originally Posted by Presence76

Hey, thanks for the replies! I did try tapping on/changing all the tubes. I've done everything except bang on it, which I will try soon. I did pull out the "guts" and noticed there is a brown substance on the electrolytic convertors. After reading the tube amp help here, it is making me think it may be those. Then my question is, if I can solder, is it something I could replace? Also, if it is those, would that be what made the noise? btw-the amp is about 5 or 6 years old...

Did you try replacing the power tubes? each and every pre amp tube?

Yes, the electrolytics can be replaced, you'll have to order them; its hard to find them in high voltage ratings needed for amps other than guitar amp parts supply sources. If you do, just don't put them in backwards, as they can explode like a firecracker!

Does it have a SS rectifier or tube?

S.B.Nichols · 02-14-2009, 02:33 PM

You can almost certainly find the needed caps (at the correct voltages) at mouser. It can be hard to navigate that interface though...if you post the mf/uf amount and the voltage ratings on the caps, I'm sure someone here can point you in the right direction.

Presence76 · 02-14-2009, 03:49 PM

Hey, thanks again! Yes, I did mean electrolyltic capacitor

I did replace all tubes (I still had the Mesa Tubes I had replaced). Tomorrow I will try to get time to take and post a picture. The brown substance is probably a glue, it's underneath as well. However, it does look as if one if the caps has shrunk back a little bit (the blue coat thats on it-whatever its called?) It will be more clear when I leave pictures...

Thanks again.

Presence76 · 02-16-2009, 01:47 PM

My original post is a little out of order. After I replaced the V4 preamp tube, it worked ok, but I didn't give it a huge workout. Well, Sunday, I played worship (1 hour practice included), and nothing happened then either. I'm going to hold off on pics, unless it happens again. Maybe it was just the V4 tube..?

Thanks again for all the help!