Express 5:50 feeds back with no instrument plugged in.

[bushman01]

Hi - I've had the Express 5:50 for about two years and love it. I've recently retubed, and have a few extra brand new tubes laying around as well for troubleshooting.

The problem I'm having is with no instrument plugged in,when I put the amp on and put the gain and master up to around 4-5, the amp starts feeding back hissing and ringing horribly. If I go to 5-6-7 on the dials it's even worse. It sounds like the clean channel wants to feed as well, but it's a little less noticable.

I followed the user manual instructions for troubleshooting tubes. I've swapped out the 6L6's with a second pair, and gone through the 12ax7's one by one. I've narrowed it down to the tube slot nearest the input jack. The wierdest thing is I've literally tried 4 different brand new 12ax7 mesa tubes in that slot. But when I completely remove the tube from that slot and power the amp on, no feedback or loud hissing. The minute I pop a tube in there and power back on hissing and feeding back starts again as I turn up the gain and master past 3 and 4. None of the other tube slots have this affect, they make no difference. There is something going on with that V1 slot, and I'm 90% sure it's not the tube.

What else could this possilbe be?
RCA cable jack to the speaker? Shielding?
I'm about 45 minutes from my nearest Mesa Dealer, I'm probably just going bring it in if it isn't an easy fix. 5 year warrantys are sweet.

Thanks in Advance..

This guy had a similar issue with a fender amp, but it seems like it's a bit different...
http://www.thefret.net/showthread.php?t=11272

 

[UKBoogieboy]

I had same problem, it was the valves, it doesn't matter if they are brand new from the shop, I was getting bad ones after bad ones brand new.

 

[Don]

By "5, 6, 7" do you mean 5, 6, 7 o'clock?

 

[Trea]

I've had the same problem with mine on the gain channel, multiple tube swaps didn't help at all. I basically don't use the gain channel. If you figure out a solution let me know.

 

[Don]

I just checked. Mine does the same thing. Fortunately, I never need my amp set up like that.

To tell you the truth, I think those settings are beyond the design limitations of this amp.

 

[vbf]

Does it behave like that with a guitar plugged in?

 

[MrMarkIII]

Since there are no numbers on the knobs, it might be more helpful to describe knob positions in terms of a clock dial, as in "5 o' clock". Just so we're all on the same page.

 

[vbf]

Also, is the reverb at max?

 

[Trea]

Mine does it with the reverb off, with or without a guitar plugged in. Anything above 11 o'clock on the volume is feedback city. Whereas I can dime the gain and master on the crunch channel with no issues at all.. Other than the fact that it's loud as hell :mrgreen:

 

[bushman01]

Thanks guys, yeah 5,6,7 o'clock

It ended up being the tubes, but they were only 2 months old.

diagnosis was "multiple microphonic tubes"

It threw me off because I followed the instructions in the manual to troubleshoot bad tubes by swappping out 12ax7's one by one, etc...Also the manual states it's rare tubes go bad. But all mine did.

It still feeds and rings a bit, not as bad. Great amp, but eats tubes.

Does running effects pedals through the inputs make your tubes go quicker?

Also I noticed to get the best tone, at least in my opinion, in the 50 watt mode, the amp has to be turned up loud. So loud my ears are ringing after 5 minutes. Great amp though, can get some great tones.

I just bought a fulltone mosfet, can't wait to try it out.

 

[Don]

The problem is not that the amp eats tubes, it's that tubes aren't made like they used to be. Mesa branded tubes aren't the best available, either.

Most decent tube amps sound better cranked. I'm impressed with how good my Express sounds at lower volume levels, even in the 50 watt mode.

 

[soundchaser59]

To tell you the truth, I think those settings are beyond the design limitations of this amp.

Not true. I've never had any of these problems when I use 12AX7's, and I can dime my gains and my master if I want. There are so many ingredients that go into this tone, and a lot of people just never test or experiment with how the pickups or the pedals contribute to unwanted sounds. I was one of them.

I had microphonics once when I put a low gain tube in the line before a high gain tube. I think I had a 12AU7 in V2 and AX7's everywhere else. I theorize the AX78's simply had too much current draw for the AU7 to deal with, just a wild guess.

Only one time did I have this problem with 12AX7's, when I put a NOS blackplate in my Subway Rocket. Both times the problem disappeared when I put in new Tung Sol or JJ tubes. And I think I've figured out that I should never put lower gain tubes in line before higher gain tubes, I am always putting the lower gain tubes last, like in V4.

Now I'm running 5751's in V1, V2, V3, and AU7 (ECC82?) in V4, and it is pretty sweet. I dont know much about it really, just saying where my little experiments have led me....

It threw me off because I followed the instructions in the manual to troubleshoot bad tubes by swappping out 12ax7's one by one, etc...Also the manual states it's rare tubes go bad. But all mine did.

I tried that too, way back when. Now I just resign myself to replacing all of them at once, after I started doing that I've not had any issues. I like the manual, but I dont trust Mesa 100%. Every tube I got from Mesa (they sent me a full set due to some dealer error) was bad outa the box or went bad within a few weeks. I will never put Mesa tubes in my amp again, never. I put JJ, Tung Sol, and Doug's Amperex and Jan/Phillips in everything now, and no more issues. I figure it's kinda like a car...... you wouldn't do a tune up and replace just one spark plug, would you?

 

[Newysurfer]

Does running effects pedals through the inputs make your tubes go quicker?

Also I noticed to get the best tone, at least in my opinion, in the 50 watt mode, the amp has to be turned up loud. So loud my ears are ringing after 5 minutes. Great amp though, can get some great tones.

ahh No - the amp doesn't eat tubes. And pedals make no difference to tubes - how could they
Had mine over 2 years and haven't had a single tube issue.
What will wear out tubes faster is
1) extreme temperature changes for people living in cold climates. Taking any hot tube amp into sub-zero outside temps and then back into heated clubs or houses will greatly increase expansion & contraction rates which vacumn tubes generally don't like.
2) pushing the amp really hard for long time periods. Cranking the master and gain on 50w for hours every day will wear out tubes much faster than if you run it at 5w and the Masters & gain never above 12 noon.

 

[bushman01]

cool, well I got my FullTone mosfet. ****, tone heaven. What a sweet pedal. Sounds great in to the clean channel of the mesa express. PLaying a strat deluxe with s1 swtiching and Samarium Cobalt Noiseless™ Strat® Pickups into the fulltone mosfet->clean channel. I'm very happy with this setup.

 

[Don]

Quoted from the manual-

p5-

"NOTE: Avoid extreme settings of both GAIN and TREBLE at the same time as the likelihood of annoying microphonic tube prob¬lems increases. If you need one set high to achieve the sound you are after, reduce the other to ensure uninterrupted performance."

p7-

"Again, we suggest using the MASTER control in its sensible ranges (9:00 - 2:00). Here, the channels will be easier to match with each other and the Effects Loop will see more reasonable signal levels.

NOTE: Because the MASTER control creates the send to the Effects Loop, extreme settings will cause a large signal to be sent to the Loop for that Channel. Not only may this cause possible overloading of the processors Input stage, but will make balancing both channel’s Effect Send level difficult."

 

[badjohnny]

Bushman01: I have a Fender Tele with those pickups. I'm thinking about using some distortion/OD pedals in the clean channel. Can you post your clean settings? I seem to have to really push the gain and master to get it loud enough. Thanks.

Johnny

 

[soundchaser59]

Quoted from the manual-

p5-

"NOTE: Avoid extreme settings of both GAIN and TREBLE at the same time as the likelihood of annoying microphonic tube prob¬lems increases. If you need one set high to achieve the sound you are after, reduce the other to ensure uninterrupted performance."

I forgot about that...... I run my tone knobs quite low all the time, usually have the treble set at 9 o'clock never higher than 11 o'clock. Maybe why I can run my master so hot and not have freq issues? Best match between loudness and noise is if I keep the master at or below 3 o'clock. The clean mode is always fairly tame though, I can use full master there, but I still dont crank my tone knobs hardly at all.

 

[bushman01]

sure im using:
1 oclock gain, just before 1 oclock treble, 9 oclock mid, 11 oclock bass, 10 oclock reberb, 9 oclock master, 3 oclock contour

clean channel


then my mosfet pedal has a volume I use to control everything. I have no volume issues, are your power tubes ok?