Maverick with microphonic tube

[John Platko]

It sounds like my Maverick has developed a microphonic tube in the lead channel.
An E3 note played anywhere seems to cause the trouble. Other notes seem fine.
The rhythm channel, which is what I usually use, sounds just fine.

Which tubes should I check first?

John

 

[MrMarkIII]

I copied this from somewhere, probably a Maverick Guy post:
(with apologies)
"V1A - clean channel 1st gain stage
V1B - clean channel cathode follower tone stack driver (only in Fat mode)
V2A - lead channel 1st gain stage
V2B - lead channel 2nd gain stage
V3A - lead channel 3rd gain stage
V3B - common 4th gain stage post FX loop
V4A - clean channel 3rd gain stage
V4B - clean channel 2nd gain stage
V5A - reverb drive
V5B - reverb recovery
V6 - phase inverter
V7,8,9,10 - power tubes
V11 - rectifier

This is a useful amp to experiment with preamp tubes in, because the two channels are almost completely independent - V1 and V4 are only used on the clean channel and V2 only on the lead channel. (The lead channel is very sensitive to V2, so if you want to start tweaking go for this one first.) V3 has a greater effect on the lead channel than the clean."

 

[John Platko]

Thanks!

It sounds like V2 is the place to start. I have a 12AX7A that I took out of an old
Hafler preamp that I could try for starters.

Are there instructions on the web for how to go about doing this?

How does one remove the preamp cover? It looks like it's being held on
by some plastic snaps. Which way do I snap them? I imagine they would
be easy to break after all these years.

John

 

[John Platko]

I thought I'd give Mesa Boogie a call and see if they can help me get the
preamp tube cover off. Turns out they only work Mon. through Thrusday - that
can't be good.

Still looking for tips on how it comes off.

John

 

[MrMarkIII]

The tips protrude from the bottom of the rectangular clamping device.
Gently push the tips horizontally toward the rear (or toward the front, if rear doesn't work) of the clamping device. Unhook the two on the long side closest to the rear of the amp, not the two on one end. The clamp will swing down, pivoting on the other two hooks. The white plastic hooks are flexible, at least to a point, so don't force them or bend them past 45 degrees. They will break, which is why many of these amps no longer have these in place.
Sorry if this is imprecise, but it's been a while since I've owned a Maverick.
Studio 22s, DCs, and many older Mesas use the same pre-amp tube clamp, so maybe those owners will chime in.
Actually removing and installing the pre-amp tubes is another topic...

 

[John Platko]

The tips protrude from the bottom of the rectangular clamping device.
Gently push the tips horizontally toward the rear (or toward the front, if rear doesn't work) of the clamping device. Unhook the two on the long side closest to the rear of the amp, not the two on one end. The clamp will swing down, pivoting on the other two hooks. The white plastic hooks are flexible, at least to a point, so don't force them or bend them past 45 degrees. They will break, which is why many of these amps no longer have these in place.
Sorry if this is imprecise, but it's been a while since I've owned a Maverick.
Studio 22s, DCs, and many older Mesas use the same pre-amp tube clamp, so maybe those owners will chime in.
Actually removing and installing the pre-amp tubes is another topic...

Hmmm. So it's the actual tips that I should be pressing on, not the plastic piece that looks like it snaps onto to the side of the metal. Thanks, that should help some.

Actually removing and installing the pre-amp tubes is another topic

Is it hard to get the tubes out once I can get a hold of them?

And while I'm learning about this. How do I remove the metal holders that are clamping the power tubes in. Do they just slide over the tubes and out of the way?

 

[John Platko]

I tried pushing the tips but that didn't do anything. Maybe I need to push harder
but I don't understand how this is supposed to work. It looks like I'll have to
call Mesa Boogie on Monday, hopefully they can walk me through it.

 

[GD_NC]

John,

Don't give up you are almost there. Not sure if you have a head or a combo but I pull the back off my combo for this. The short heads are really tight. You might want to take the front panel off if it's one of those.

The tube cover is really not hard once you understand how it works. It's essentially a U shaped metal plate held on by 4 white plastic arms. There should be two arms on each side of the plate. Each plastic arm has two parts holding the plate. One is straight and pointed going into a hole in the plate. The other part is a clip that slides over the outside edge/lip of the plate parallel to the pointed part. To get it off grab both of the clips on one side at the same time and pull them toward you. Then, while holding the clips, push the plate down below the end of the pointed part. Once you have one side free repeat the process on the other side. (or just undo one side swing and it out of the way for a quick tube change.)

To find a microphonic tube. Go get a wooden stick (chopsticks are good. Pencils are NOT), turn your amp on, remove anything from the input, turn it up fairly loud (at least 50% volume), then tap on the tubes very lightly while you amp is on. Repeat the process on the 2nd channel. Check the power tubes too. The offending tube will usually ring loudly and possibly start to squeal when you tap it.

If it's feeding back before you start tapping. Turn the volume down lower and gently touch the stick to each tube. Usually holding the stick to the bad tube will make it stop or reduce the ringing.

good video on the topic... http://www.youtube.com/watch?v=QM2qWZYbInI

Good luck.

 

[John Platko]

John,

Don't give up you are almost there. Not sure if you have a head or a combo but I pull the back off my combo for this. The short heads are really tight. You might want to take the front panel off if it's one of those.

The tube cover is really not hard once you understand how it works. It's essentially a U shaped metal plate held on by 4 white plastic arms. There should be two arms on each side of the plate. Each plastic arm has two parts holding the plate. One is straight and pointed going into a hole in the plate. The other part is a clip that slides over the outside edge/lip of the plate parallel to the pointed part. To get it off grab both of the clips on one side at the same time and pull them toward you. Then, while holding the clips, push the plate down below the end of the pointed part. Once you have one side free repeat the process on the other side. (or just undo one side swing and it out of the way for a quick tube change.)

To find a microphonic tube. Go get a wooden stick (chopsticks are good. Pencils are NOT), turn your amp on, remove anything from the input, turn it up fairly loud (at least 50% volume), then tap on the tubes very lightly while you amp is on. Repeat the process on the 2nd channel. Check the power tubes too. The offending tube will usually ring loudly and possibly start to squeal when you tap it.

If it's feeding back before you start tapping. Turn the volume down lower and gently touch the stick to each tube. Usually holding the stick to the bad tube will make it stop or reduce the ringing.

good video on the topic... http://www.youtube.com/watch?v=QM2qWZYbInI

Good luck.

Thanks I'll give that a try. It seems that it takes a fair amount of force to get the cover off, is that right?

The amp isn't microphonic all of the time. It seems to be sensitave to the note being played. Around E2 is the problem. Also, it seems to need to warm up a bit before it shows up. It's only in the lead channel. Does that sound
like a microphonic tube?

My Maverick is a 2X12. I posted some pictures a while back, here's the thread.

http://forum.grailtone.com/viewtopic.php?f=4&t=31136&p=228500#p228500

 

[GD_NC]

Thanks I'll give that a try. It seems that it takes a fair amount of force to get the cover off, is that right?

The amp isn't microphonic all of the time. It seems to be sensitave to the note being played. Around E2 is the problem. Also, it seems to need to warm up a bit before it shows up. It's only in the lead channel. Does that sound
like a microphonic tube?

Yes, those little clips are very tight so don't be scared to force them. If they do break you can order new ones from Mesa for a couple of bucks. No big worries. I've had a mav, dc-2, & dc-3 over the past few years. So far, I've never broken a clip.

Most microphonic tubes come and go at first. Being sensitive to specific notes/frequency is not unusual. Don't overlook the power tubes. EL-84s are get really microphonic when they get old. Bad tubes really start to misbehave as they are stressed. So I keep one hand on the volume.

Don't rule out more than one bad tube! That can make it a bit harder to find the problem. Also note the first tube in the preamp chain will always be the most sensitive to noise.

 

[John Platko]

I got the preamp cover off today. It actually worked ok once I had a better idea of what
I was trying to do. Thanks folks.

I tried swapping V2 out but it didn't change the problem. Then I tried
swapping V3 out, it didn't change the problem either. I assume the
tubes are numbered in order starting with 1 being the closest to the
input jack. Is that right? I didn't see if the lead channel stopped working
when I pulled a tube.

I can't say that I noticed any difference with the hafler tube instead of
the Mesa Boogie. At least nothing blew up.

Is there any point in trying to swap out the phase inverter? I can't say
that I notice the problem with the clean channel - although sometimes
I think I hear a tinge of it but ears can play tricks like that on you.

I also tried using the solid state rectifier and convinced myself that
the problem is less present in that mode. It's still there though but
it seems to come and go more. It mostly sounds like a buzzing guitar
string but it's not, I've tried a few guitars and they all do it - more or less.

Any ideas?

John

 

[GD_NC]

John,

Change your power tubes. That sounds like a classic case of EL-84s gone bad. Those tubes run really hot and don't last that long.

 

[John Platko]

John,

Change your power tubes. That sounds like a classic case of EL-84s gone bad. Those tubes run really hot and don't last that long.

I think you're right. As I was poking around I noticed that one of the EL-84s wasn't sitting straight in its socket. It was partially out. I pushed it back and that seemed to help, although I could still hear the occasional microphonic. Then I got a stick and tapped all the tubes. I didn't get anything from the preamp tubes. One or two of the EL-84s made a very slight sound that had a lot of the character of the microphonic. After the tapping the microphonic was gone - at least for now. It's funny how it doesn't show up in the clean channel but maybe it has something to do with the voltages the power tubes see when in lead mode.

So as I understand it, I need to replace the power tubes in pairs. Right?

Which tubes make a pair in a Maverick? You would think this kind of info would make it in the manual but it didn't.

How does one remove those metal wires that are acting like seat belts and holding the power tubes in? They seem to be very tight.

John

 

[GD_NC]

In a Maverick all the power tubes should be replaced at once. Just push the retainer clips back and they will pop loose. If you use your amp often you should change your power tubes once a year. EL-84's are relatively cheap and crap out really fast. You will be amazed at how much better it sounds.

 

[John Platko]

In a Maverick all the power tubes should be replaced at once. Just push the retainer clips back and they will pop loose. If you use your amp often you should change your power tubes once a year. EL-84's are relatively cheap and crap out really fast. You will be amazed at how much better it sounds.

Why does the Marverick need all power tubes replaced at once?

I got the preamp cover back on with no problems. If you know how it works it's not so bad
of a design. Of course, I woudn't think that if the plastic clips broke.

The nasty microphonic seems gone for now. I think the combination of putting the tube completely
in the socket and giving it a rap made it go away. I'll see how long it takes to come back and also
plan on getting some new tubes.

Thanks for the help folks.

John