broken mesa dual rectfier

[ofwolves]

so's this guitar amp of mine has definately seen better days.

its ailments really started around a few years ago. bad grounding.
operating with bad tubes. but all of this was fixed a year or so ago.
when the output transformer was replaced along with all new tubes.
of course the grounding was fixed as well.

the amp worked great for about a year when the thing after being
turned on and played for about five or so minutes would just peeter
out. this was like two monthsago. i figured that maybe it was the power tubes and bought some new ones. after replacing them the amp did seem to work for like one band practice. the next practice two days
later the thing just did not want to work after 20 minutes of being on.

thing is it looks like the grounding at our practice space is non existent.
wtf?! maybe not though. as in there are two other bands that practice there
who don't seem to be having any problem with their stuff. our bass player
started to have problems with his amp six months or so ago. so who the
hell really knows!? not me.

any ways i was wondering if any tape-oppers out there had any idea of
what the problem with this thing could be. output transfomer maybe?!

any input would be appreciated.



mark

[Milkmansound]

you cant just put new output tubes in without biasing the amp or at least checking that the bias voltage is even there. Chances are you put tubes in, and burned them up in the 20 minutes you ran them because they were not biased properly. Take it to a tech!

[ofwolves]

i failed to mention that this amp is designed in a way that does not
require any biasing. don't ask me how this works but i do know this
to be the case after reading the owners manual.

luckily mesa have a tech phone number. that i will be calling tommorrow.

thanks for the input though.

[Randy]

i failed to mention that this amp is designed in a way that does not
require any biasing. don't ask me how this works but i do know this
to be the case after reading the owners manual.

luckily mesa have a tech phone number. that i will be calling tommorrow.

thanks for the input though.

The only thing I have to add is that since they are permanently biased like this, you have to buy the tubes from MesaBoogie. They match the tubes to their circuit. A matched pair of any other type of tube will have something like a 1 in 30 chance of hitting the right plate voltage requirement, and other measures. So, for instance, iIf you are putting in matched pairs of Groove Tubes, they are blowing because they are running way too hot, or other things in the amp are pupping out because the tubes are running too cold.

I had a friend who bought a Subway Blues used, so it didn't have a manual. He kept blowing tubes and having tubes go microphonic and he eventually sold it at a loss because it was "broken."

[ofwolves]

the tubes i used were mesa all of the way.

[rockstudio]

Hey mark, Mesas are notorious for developing hard-to-fix problems, or recurring problems. Does the Dual Rec have Rectifier tubes, or are you using the solid state diodes? I have been helping one of my buddies with his triple rec that would blow tubes and burn the safety resistors above the tubes, he pulled his rectifier tubes and sticks to the silicon diodes. For better or worse tone, they help protect the power tubes. If you have the money, get your head to a certified technician.
Take a look at the tubes when you turn your amp on. leave it on standby and look at the tubes, then hit some chords at a low volume and watch them. sometimes they will have a blue/purple corona all of the time, sometimes only when you are playing. If one of your tubes is looking very different from another, there is very likely to be a problem in that pair's circuitry (the tubes work together in pairs, if there are 4 tubes in you head, there are two pair, - 100 watts, 6 tubes- 3pair- 150 watts in most cases). Some mesa heads have a low power mode (tweed mode, whatever) that will put one pair of tubes on standby and utilize only the other pair for power.

The grounding in your practice space should be addressed. Non-existent grounding will be bad for any equipment if that equipment develops a short and high voltage (lethal) has no way to get to earth and flip the circuit breaker or blow a fuse. You would notice this if you touch your lips to a microphone while playing your guitar and you receive a shock.

Grab your multimeter or one of those outlet testers from the hardware store and check it. One of the lugs should be connected to ground at the breaker box, so it would beep on a continuity test with your meter between the "white" lug and ground lug. if this outlet fails the test grab one of the grey non-grounding outlet adapters and screw it onto the center screw of the outlet plate. The screw should be in contact with the conduit surrounding your a/c supply and should go back to ground at the breaker box.

As far as biasing goes, you are doing the right thing by sticking with mesas, you really have no other options (you can get different hardness-rating tubes from mesa for different distortion parameters). Biasing simply sets the null point for the tube with respect for a waveform as to have equal amplitude above and below the null point, or crossover, minimizing crossover distorion (between gain stages) and offset voltage. Probably won't burn up a tube.
Peace out to the max.

[RefD]

Mesa Dual Rectifier amps are switchable between tube rectifiers and solid state bridge rectifiers and have both installed, hence the name "Dual Rectifier".

and, regardless of what MB say in their propaganda, their amps DO need rebiasing and rebalancing when you retube the output section and it requires surgery.

*stomps across lawn at 3am in baggy boxers and threatens imaginary teenagers with rake*

[rockstudio]

RefD, do you mean Mesas need bias adjustment when you re-tube, or when you re-tube and do surgery? Mesa boogie only sells tubes that spec out perfectly ($$$). They color code all of their power tube sets, so you know that your replacement tubes will be very similar to your old tubes.

Dual Rectifier means that their are two rectifier circuits, needing two rectifier tubes, or switching to the built in diodes. triple recs have three rectifier tubes or three sets of built in diodes.

[RefD]

RefD, do you mean Mesas need bias adjustment when you re-tube, or when you re-tube and do surgery? Mesa boogie only sells tubes that spec out perfectly ($$$). They color code all of their power tube sets, so you know that your replacement tubes will be very similar to your old tubes.

they need rebiasing and rebalancing and it feels like you're performing surgery on the Westinghouse robot.

the amp biasing is never dead-on, really, and the tubes MB sells now are not what they sold in '89 or even '94, matching or not.

thank you, corner-cutting.

disclaimer: this is largely my opinion based on my personal experience, i am not saying i am 100% correct.

Dual Rectifier means that their are two rectifier circuits, needing two rectifier tubes, or switching to the built in diodes. triple recs have three rectifier tubes or three sets of built in diodes.

aye, twas what i was trying to say.

[rockstudio]

sweet. You're right, the inside of a Mesa is entirely too crowded with PC boards and all that stuff, you have to take every knob off to look at anything inside. I love my old amps, just wires and components and fresh air.

[RefD]

I love my old amps, just wires and components and fresh air.

hellz yeah!