Help! Massive Mark V Problem!

[SickBoy87]

Hi everybody!

Just wanted to turn my Mark V on, but theres no Power!
Checked the Fuse and it was blown away...Just put in a new one - turn the Power Switch on and another Fuse
was gone...What's wrong with the Amp? Just wrote an E-Mail to the Store i bought it, but just want to do
some Trouble-Shooting by myself - maybe the Power-Tube is gone??

Please help...

THX!

 

[screamingdaisy]

Read the manual. It has a whole section on diagnosing tube failures...

 

[Scary]

It's not a massive problem yet, probably just a bad tube.

 

[rabies]

massive problem is really only if your output tranny and/or power tranny are damaged as they are typically the most expensive components in a tube amp.

it's most likely a power tube failure, swap in a known good EL34 or 6L6 one at a time and replace the fuse (same rating, slo-blo) simultaneously.

 

[rabies]

sometimes the screen grid resistors blow as well when a power tube fails, then you typically have to take the amp to the shop unless you're electronically savvy...

 

[SickBoy87]

Tomorrow I'll take it back to the shop.
But there must be the Reason, why the Power Tube makes Problems - the Amp is only 4 Months old!

 

[RocknRory]

you didnt accidentally switch it to EL-34 when its using 6L6s or visa-versa did you?

 

[Barry]

that almost has to be a power tube

 

[Barry]

Tomorrow I'll take it back to the shop.
But there must be the Reason, why the Power Tube makes Problems - the Amp is only 4 Months old!

thats the nature of tubes , they can last 10 minutes or several years . I got my Mark V in January and had to replace a 12AX7 and a rectifier tube recently

 

[domct203]

If the fuse is blowing when you turn on the main power (still in standby) chances are that it is a bad rectifier tube.

Make sure the amp is set to diode rectifier, 45W or 90W. Remove the rectifier (5U4GB) tube. Power on the amp. If you do not blow a fuse, the rectifier tube is the bad tube. If you blow a fuse when coming out of standby, most likely it is a bad power tube. You need to remove the rectifier tube because even in diode mode, the tube is still in the circuit.

In most cases a blown screen grid resistor will not blow a fuse as it is an open circuit. Also, the socket with the blown resistor will be electrically "off".

As mentioned, RTFM.

Good luck.

Dom

 

[Melodyman]

Tomorrow I'll take it back to the shop.

Cut out the middleman and contact Mesa directly. Tube's might only have a 3 month warranty or 6 I forgot.

 

[phyrexia]

six month warranty on the power tubes.

 

[nsgelocos]

I had a similar problem that I thought would result in sending the amp in to get it fixed. According to repair shops, I had a shorted diode. The amp was blowing fuses when I turned it on. We sent an email to Mesa and got a reply that said in caps "don't send that amp anywhere, call us immediately". The problem was a shorted 5U4GB rectifier tube. A test of removing tubes till the problem was isolated and ordering a new rectifier was the remedy.

 

[Drahthaar]

I am pretty certain it is something your local repair tech can fix. I had something similar happen back when I had my roadster. When turning the power on soon as the switch was flipped it would immediately blow a fuse. Turned out to be a varistor. Took it to the local tech and all he had to do was replace the varistor, a pretty minor fix. When it happened we were playing an outdoor show that was powered by an industrial size generator. Thus it was not covered under warranty because Mesa said it was due to a power surge and the problem was caused by something external to the amp and not a fault of the amp.