Mark V not working :(

[billbixby]

Any ideas? I pulled the 6L6's to try EL34's that I have used in the past. Amp off, pulled 6L6's, put in EL34's and flipped the switch to EL34 and poof, fuse blew. Tried another fuse, blew again. Put in the 6L6's back and flipped the switch to 6L6 and fuse blew again.

I have used these EL34's before.

Any ideas? Think it could be the 5U4GB? Which of course I do not have.

 

[psychodave]

Could be the rectifier. Change out all power tubes. I would change out all tubes to be sure since I've seen where a preamp tube caused an issue further down the circuit, but I don't remember what amp or the circumstances.

Make sure to check everything and makes sure you are using the correct slo-blo fuse.

 

[steve_k]

the fuse blew before you took it off standby? make sure you aren't in a half watt or low watt setting in rectifier mode.

 

[billbixby]

the fuse blew before you took it off standby? make sure you aren't in a half watt or low watt setting in rectifier mode.

Rectifier mode? Oh you mean channel 1 and 2 right? I use channel 3. Channel 2 and 1 are set to tube, not diode.

I run channel 3 in 10 watt mode. I put the tubes in (EL34's) with power off, switched the switch to EL34, then turned it on in standby mode, let it warm up, switched it to on and played for 3 seconds and it shut off.

Fuse was blown. Replaced fuse 2x, resulting in 2 more blown fuses. Put 6L6's back in, turned switch to 6L6 mode, turned on in standby mode and instantly blew another fuse.

 

[steve_k]

the fuse blew before you took it off standby? make sure you aren't in a half watt or low watt setting in rectifier mode.

Rectifier mode? Oh you mean channel 1 and 2 right? I use channel 3. Channel 2 and 1 are set to tube, not diode.

I run channel 3 in 10 watt mode. I put the tubes in (EL34's) with power off, switched the switch to EL34, then turned it on in standby mode, let it warm up, switched it to on and played for 3 seconds and it shut off.

Fuse was blown. Replaced fuse 2x, resulting in 2 more blown fuses. Put 6L6's back in, turned switch to 6L6 mode, turned on in standby mode and instantly blew another fuse.

that's an odd one for a mesa. they are biased so cold that even the hottest of tube shouldn't bother them, unless something has happened in the switch circuit for the 6L6/34 select. maybe try it again with the outer pair only, see what happens. then, the inner pair and see what happens. make sure its not in triode mode.

this one may need a trip to petaluma though.

 

[some dude]

Despite being used before one of the EL34s may be pooched and taken something out. One of the 10¢ parts with a $100 bench fee.

From what I understand the Mark V's EL34 mode is biased quite hot... Somewhere up near the top of the operating range when used with their own tubes.

 

[steve_k]

Despite being used before one of the EL34s may be pooched and taken something out. One of the 10¢ parts with a $100 bench fee.

From what I understand the Mark V's EL34 mode is biased quite hot... Somewhere up near the top of the operating range when used with their own tubes.

i may be wrong, but i think that is in triode mode where it sends the outside sockets into a class A mode. this is why mesa doesn't recommend the mixing of tubes in the V like the predecessors. can't remember exactly.

but yes, could have blew a screen. pull the chassis and have a look around for a burnt resistor.

 

[some dude]

I think the non-mixing is due to 10w mode using 1 tube from the inner pair and 1 tube from the outer pair. Rumor was mixing tubes could damage the OT.

I have an early Mark V where it explains how to mix tube types in the manual... They quickly deleted that part in later editions. Makes me wonder how many amps went in for warranty work before that was sorted.

 

[billbixby]

THIS KID <<<<< IS STOKED

Found amp repair guy 5 minutes away. I put up an ad a while back online local, looking for a tube amp repair guy and forgot this guy responded. I took like an hour going through past emails looking and found his number. Called him up and dropped the amp off earlier. Calls me back a short while ago, rectifier tube blown.

Of course I didn't have a spare, so I couldn't test that. He doesn't have one to sell either, but the guy is so damn cool, he's ordering me a couple and is going to let me use his till they come in. How cool is that?

This guy saved me as the nearest Boogie repair place is like 75 miles away.

I have no idea why the damn thing blew just swapping tubes, but I'm scared to use the EL34's in the thing again. He tested all my tubes and said they all read like brand new, even the EL's, so I have no idea what happened, but I got lucky.

 

[blackba]

THIS KID <<<<< IS STOKED

Found amp repair guy 5 minutes away. I put up an ad a while back online local, looking for a tube amp repair guy and forgot this guy responded. I took like an hour going through past emails looking and found his number. Called him up and dropped the amp off earlier. Calls me back a short while ago, rectifier tube blown.

Of course I didn't have a spare, so I couldn't test that. He doesn't have one to sell either, but the guy is so damn cool, he's ordering me a couple and is going to let me use his till they come in. How cool is that?

This guy saved me as the nearest Boogie repair place is like 75 miles away.

I have no idea why the damn thing blew just swapping tubes, but I'm scared to use the EL34's in the thing again. He tested all my tubes and said they all read like brand new, even the EL's, so I have no idea what happened, but I got lucky.

Great news. Those modern rectifiers are not as reliable as the older ones, so not too surprised that is what went out.

As an up And coming tech myself, its so nice to get someone's amp working.

 

[billbixby]

He was urging me to get a NOS rectifier tube for $40
He said it would outlive me?
I opted to go for 2 regular ones for $15 each. Wonder if I should have got a NOS one or if I can get one online?

 

[psychodave]

Congrats. First rule is to change out tubes

 

[blackba]

He was urging me to get a NOS rectifier tube for $40
He said it would outlive me?
I opted to go for 2 regular ones for $15 each. Wonder if I should have got a NOS one or if I can get one online?

I would have gone with the NOS rectifier tube, $40 for a NOS 5U4GB is not a bad price. The new rectifier tubes don't have the greatest track record, I have had some last a long time and others not so much.

 

[BackCrack]

Doesn't running in 90w mode bypass the tube rectifier for silicon diodes?