MY MT 15 Problem

[Befuddled]

This doesn't happen every time but when we are playing after 15 minuets or so disturbing noise starts coming out the speaker. It renders the combo useless until the head is put in standby and then turned back on. Like a reboot if you will. I don't know what to do. The problem is that it doesn't do it every time so trouble shooting could be difficult. Any suggestions would be very welcome. Thanks.

 

[TRGuy]

Have you emailed the PRS guys? In my experience, they're excellent to deal with. I've chucked loads of difficult questions at them before that they've been incredible at answering.

 

[GuitarJammin]

Now there is a lot of things that it could be. However if this was happening to me I would do these things. When it happens again see if you can see a tube starting to glow brighter than the others. When amp is cooled completely off, look for signs of white sheen on a tube. On the MT 15 you can probably just look through the grill with a light to search. There may not be any signs at all though. Those would be my first moves at least. I would be blaming tubes myself...since most of the time it seems a tube has been my problem.

 

[Beach Dog]

Im having the same problems...also a volume drop with a bit of muffling occurs in both channels? The PRS MT15 and PRS cabinet are about 4 months old...any additional thoughts?

 

[Deleted member 5962]

Have you checked the tubes? 99% of the time, that's the issue. If you have and if they are all known to be good, then contact your dealer or PRS.

 

[andy474x]

I agree with the tube notion. I would start with V1, put a new 12ax7 in and see if the problem goes away. If not, just go down the line.

 

[Beach Dog]

Have you checked the tubes? 99% of the time, that's the issue. If you have and if they are all known to be good, then contact your dealer or PRS.

thank you...do you think they could go bad in 3-4 months of daily use for maybe 2 hours/day? what are some of the visual traits i should look for to determine if the tubes might be bad? thanks again...

 

[Deleted member 5962]

Absolutely. I’ve had tubes go bad in a few weeks, that were new from a trusted source that tests them thoroughly, but that doesn’t happen often. They can certainly go bad prematurely. You should have spares at all times. Take a known good or new tube and replace them one at a times, starting with V1. If none of those do it, try the power tubes. If one of them isn’t bad, then it might need service.

Sometimes, yes, you can visually see a bad tube, but not always. If one is blowing much brighter, or much dimmer, than the others, that can be an indicator. If you can’t, just start rolling them as suggested above.

We’ve all had tubes that lasted years and after a while even lost good tone, but still functioned perfectly. And I’ve had newer ones go microphonic and or fail.

 

[Boogie]

It absolutely is a tube. Every amp owner needs spare tubes anyway, so get a spare 12ax7 and a pair of 6L6s. Start systematically swapping out the preamp tubes first, then replace the pair of power tubes if nothing comes of the preamp tests. You’ll find the culprit. Be sure to let PRS know because tubes should last longer than what you’ve experienced. This stuff happens to every amp maker.

 

[Beach Dog]

Absolutely. I’ve had tubes go bad in a few weeks, that were new from a trusted source that tests them thoroughly, but that doesn’t happen often. They can certainly go bad prematurely. You should have spares at all times. Take a known good or new tube and replace them one at a times, starting with V1. If none of those do it, try the power tubes. If one of them isn’t bad, then it might need service.

Sometimes, yes, you can visually see a bad tube, but not always. If one is blowing much brighter, or much dimmer, than the others, that can be an indicator. If you can’t, just start rolling them as suggested above.

We’ve all had tubes that lasted years and after a while even lost good tone, but still functioned perfectly. And I’ve had newer ones go microphonic and or fail.

Great advice...i'll try it right away. The second set is a good idea...Thanks again!

 

[shimmilou]

You absolutely should bias the output tubes if you change them. Preamp tubes are plug and play, no biasing required.

 

[Tremontinator]

This doesn't happen every time but when we are playing after 15 minuets or so disturbing noise starts coming out the speaker. It renders the combo useless until the head is put in standby and then turned back on. Like a reboot if you will. I don't know what to do. The problem is that it doesn't do it every time so trouble shooting could be difficult. Any suggestions would be very welcome. Thanks.

Start isolating the problem. Try a different cabinet

And then a different cable from head to cab

Remove FX from the loop

 

[Beach Dog]

You absolutely should bias the output tubes if you change them. Preamp tubes are plug and play, no biasing required.

Just ordered the tubes...2 6L6 GCM and 6 JJ ECC83 about $120...not too bad. The "Tubestore" was awesome and spent a tremendous amount of time educating me about the diversity of tubes and there many purposes/sounds etc. They agree with you and highly recommended getting the power tubes biased. thanks for the advice!!

i thought about the second set but the order should be here in 2 days and i figured that i can be down a few days as i have other amps as well (although i virtually never use them anymore...solid state garbage).

 

[Deleted member 5962]

I suggest you don’t just throw a whole new set of tubes in there... try them one at a time in the preamp stage, as I suggested to find the problem. You don’t want to replace 5 tubes that may last another year or so.