Mark V problem, can you help... [tubes,wattage,cautionlight]

[NateAHM]

Hello all, I haven't logged nearly enough time on my Mark V but I'm trying to change that...I've run into a problem though...

Typically I play with all channels in 90 watt mode, but I wanted to try the others out...but I discovered that 45 watt and 10 watt didn't work when I switched to those settings.

I noticed that the caution light was illuminated on the back of the amp, but the bias switch was and always has been in the correct position, to EL34s as that's what I'd been using.

I came back to the amp today and tried to figure out the issue. I switched Ch. 1 and 2 to Diode mode in the 45 watt setting and found that it DID work. But when I switched the toggle to tube, neither 45 watt setting worked. None of the channels worked on 10 watt mode.

I continued playing when all of a sudden a loud crackling came through the speakers. I looked on the back of the amp and the 2nd EL34 from the right was glowing much more strongly than the others, so I powered down and figured the tube was dead and I needed to change tubes.

I had a spare set of 6L6s, so I put those in the amp. When I did so, I adjusted the bias toggle to 6L6, and powered on the amp. The caution light did NOT come on this time. BUT, the same issue continues; I can't play at all on the 10 watt setting, and only on Diodes in 45 watt mode.

Sorry for the long post, but anyone who can help, that would be great...I don't want to be unknowingly causing my amp damage. Could it be that the 5U4 tube has gone bad, and therefore I can't play in certain watt settings? Why was the caution light on when I was using EL34s but not now that I have put in 6L6s? Was the caution light just warning me that one of the EL34s was about to die, as it recently did?

Any help would be awesome!

 

[phyrexia]

red light just means the bias is set for el34s. no caution. just alert. notice it turns on as soon as you flip the switch from 6L6 to EL34.

your recto tube is dead. the amp functions when diode rectified but not when tube rectified.

 

[NateAHM]

thanks a lot man, I thought so but wanted to confirm it!

so the power tube dying was just a coincidence?

 

[domct203]

thanks a lot man, I thought so but wanted to confirm it!

so the power tube dying was just a coincidence?

I've been around tubes long enough to know there is no "coincidence" with them LOL.

How old are they? Are they Mesa EL34's?

Dom

 

[NateAHM]

Hey man, yes, they are Mesa tubes, and I got the amp from its first owner around June of 2010. So I've had the amp for about 8 months, but it's had the EL34s in it for probably only 3-4 months of that time. It came with Mesa 6L6s and EL34s and only fairly recently did I realize I liked the 34 sound better.

The tubes have sounded perfectly fine; I'm not sure how long the Rectifier tube has been out of commission, it could have been a couple months for all I know, as I said I pretty consistently am on 90 watt mode.

But, when I was trying to get the other watts to work I did do a significant amount of toggle switching between watts, could this have worn down the 34s faster? Also, I never use Variac power, they are running full all the time.

After the crackling speakers and noticing one 34 was definitely glowing more than the others and I replaced them with 6L6s, everything seems to be in working order. Rectifier tube still dead though.

Could any other info help you diagnose the problem? Do you think I'm safe running these 6L6s without another tube spontaneously dying?

 

[rocknroll9225]

red light just means the bias is set for el34s. no caution. just alert. notice it turns on as soon as you flip the switch from 6L6 to EL34.

your recto tube is dead. the amp functions when diode rectified but not when tube rectified.

everything he said is correct. the amp always uses the tube rectifier in the 10W setting and in the 45W setting on Ch1 and Ch2 if theyre set that way. just pop in another 5U4 and youre good to go. the EL34's might have been stressed too hard (resulting in that really bright glow), so idk if theyll still be good to use. my guess is that they were affected basically the same way they would be if you just flicked the main power switch on and off without hitting the standby switch; they probably got regular power when you set it to diode but got essentially turned off when you turned on the tube rectifier, making them wear abnormally fast.

 

[iceman]

I've had a similar problem but probably a different root cause. When switching to 10 or 45 watts nothing. However when I switched it back and tried again it worked. I'm guessing dirty contact in my case. Although it did happen on channels 2 and 3.