Power tubes not turning on!

[major7th]

Hey guys, got a strange on here.
Last night I was on stage and turned on my Mark ivb rack mount to soundcheck. Put it to full. standby off. No sound. Checked wireless, other cables, nothing. Had all light on, just no sound. Quickly I reached for the speaker cable, but it was fine.
I get down to look into the rack my power tubes were all dark!
Before panic set it, I reached over a lightly moved the 1st 6L6 and boom,they all light up.
Gig went fine.
Weird.
I get home and set everything up. Same thing! Reach down and touch a power tube, and they all come on.

What is going on?

 

[zodiac272]

maybe a loose pin not making a good connection?

scott

 

[mark2boogie]

major7th,

If the tubes are not "lighted" = not heated, that means that there are no 6.3V to the output tubes, or even to all tubes. So :

1 - or there is a short-circuit on the heater line, occurring in the wiring or inside a tube (shorted heater)

2 - or there is a cut somewhere on the heater line (cut trace or wire)

The problem may be alternative or permanent, or occuring when hot, or in case of schock... Here's what you can try for a 1st diagnosis :

- remember the tube you moved to heat them on, and try to move it again to see if provokes the heating intermittence.

- if yes : the tube may be suspect, or the heating circuit close to him may be suspect.
- so : try another tube and see if the problem persists.
- if yes : the tube is not responsible, it's the heater circuit or another tube.
- if no : the tube may be faulty.

- if no : the heating circuit has a hidden cut or even a short somewhere (more rare, but more dangerous for your amp)
- so : it's best to stop and see your repairman for a more accurate diagnosis and maintenance.

Intermittence issues are sometimes pest to trace and cure...

A+!

 

[major7th]

Sent it in to boogie. They did the work in less than a week!! $100.00

I had a burned resister and a frayed heating line. I have my mark iv in a non shock rolling rack. I'm thinking it might have had something to do with it.

I've got a 10 space shock rack that would be better, but loading it in and out!!!

 

[dodger916]

Thanks for the update.