Mark V fuse blown, HELP!!

[thrasher10000]

Recently a was happily rocking out on my Mark V when out of nowhere it just completely lost power.

I noticed the fuse was blown so replaced it then rebooted it and inspected my power tubes. Here I noticed as soon as I took the amp off standby the left of the center 6l6 pair was glowing red hot.

At this point I assume that tube has shorted and take it out replacing both center 6l6s with ruby 6l6s I know are fine from my 6505. Boot it up again, same problem!! :roll:

Now the ruby tube in the center left position glows ridiculously bright and starts to emit a burning smell, it's neighbor on the center right appears to be fine.

Any idea what the problem could be here???

 

[Chester]

Were your tubes Mesa bias rated?

What were your power settings when the fuse blew?

 

[cradlefish]

Get a quad matched 6l6 along with a new fuse and try that. It's always a good idea to keep a fresh set of matching set of power tubes on hand and some preamp. It's a tube amp and if you're tube amp owner. It is always wise to have them at your disposal so you won't second guess what the problem could be.

It's like a light bulb in the house. I'm pretty sure you have extras laying around in case one gets burned out.

If more tube amp owners use that analogy. It could save them alot of trouble.

 

[thrasher10000]

Were your tubes Mesa bias rated?

What were your power settings when the fuse blew?

Yes I was using all mesa 6l6 tubes when it failed, then tried ruby tubes for comparison with the same result. Which ever tube is in that number 2 power tube slot gets fried :/

I was running it at 90w, variac, channel vol 10-11 o'clock (high I know) Loop bypassed

 

[thrasher10000]

Get a quad matched 6l6 along with a new fuse and try that. It's always a good idea to keep a fresh set of matching set of power tubes on hand and some preamp. It's a tube amp and if you're tube amp owner. It is always wise to have them at your disposal so you won't second guess what the problem could be.

It's like a light bulb in the house. I'm pretty sure you have extras laying around in case one gets burned out.

If more tube amp owners use that analogy. It could save them alot of trouble.

Yeah I tried a fresh quad by stealing the 6l6s from my 6505 but got exactly the same result. Maybe the fuse blowing threw out the bias or something...

 

[bandit2013]

Do not forget to replace the Rectifier tube. That can also be cause for blowing fuses.

V8 will be the hot tube while the amp is set for effects loop active, it will switch to V9 in hard bypass. in both 45W mode, V8 and V9 operate in extended class A, not quite A/B. 90W mode pulls in V10 will parallel V8, V11 will parallel V9. Even in 90W, if you have loop active, V8 will still be the hot tube, V9 will be the hot tube with effects loop in hard bypass. You should replace the PI (V7) preamp tube in case one of the triodes is not operating. If the PI tube is only operating partially, or not balanced, you wind up overloading the hot tube. My amp was burning up V8 especially in 45W mode, power setting did not matter. After replacing the PI tube, and all power tubes including the Rectifier tube, the amp runs really good and seems to operate more evenly. One issue may be working against you, if the tubes are not matched properly this will happen as well.

Also, most amps of different make will not operate the power tubes the same way the patented Mesa Simil-Class operates. Most other amps run Class A/B so out of match tubes may not be of major concern, also if they have bias adjustment, you are basically compensating for the mismatch. Fixed bias amps, they are set what would presumably be optimal, if there is considerable drift in one tube, the other tube used to counter balance V8 with V9 will be taken down with it once one of them draws more current than they are capable of handling. Not all tubes from various sources are perfectly matched. After some use they can drift (depends on tube manufacture). What may work fine in one amp may not be okay in use in another amp. I had tubes that worked perfectly in the my Mark V, tried them in my Mark IV to hear the difference and they got toasted the second I switched the standby. I have done the same with tubes borrowed from the Mark IV when I burned up the original tubes that came with the Mark V.

 

[davila182]

Hey, I blew fuse in my mark v, replaced fuse and blew again. Not sure what's going on. Any suggestions?

 

[Hypnotoad696]

Find an authorized tech in your area? Also +1 on changing the rec tube if you haven't..

 

[thunda1216]

yep - the rectifier tube, especially the chinese ones fail often and cause the fuse to blow. if possible, find a nos USA made tube, they last a lot longer. the chinese ones sound great but have a really short life span.

 

[bandit2013]

I believe the 5U4GB Mesa Branded and Electro Harmonix are one in the same rectifier tube. I have yet to have an issue with the Roadster which has two. However, the 5U4GB has it's limitations. If the power tubes are drawing more power than the 5U4GB can handle it will be the first thing to go. I found the Mark V to be harder on tubes than other Mesa amps I have or have had in the past. If you are having power tube issues, blowing fuses, and or power supply problems (killing the rectifier tube) definitely have the amp looked at by qualified Mesa Tech.

Try pulling out the 5U4GB (will only work in 90W mode, or 45W mode if set to diode on CH1 and CH2) and if the amp powers up then it is Rectifier related. If it blows suddenly it may be power tube related. May also be preamp tube too but usually power tube will be the fault.

 

[BoogieHog]

And as I have discovered THE HARD way, put the tubes in forward and not backward. Follow the Tube key and MAKE SURE it lines up with the key slot on the tube insert on the Amp.

I feel like a IDIOT having to say that but, if it saves someone some money then it's worth it.