Loud, audible "pop" when switch from 5 to 15 watt mode.

[Jared Purdy]

I have read this elsewhere (not sure if it was here), and mine is now doing it in either the 1st channel or the 2nd channel. It doesn't do it when switching from 15 to 30, or back to 15 from 30, but it does it back and forth form 5 to 15. It started doing it today (I noticed), and coincidentally, the amp blew another fuse and new (2 weeks old) Mesa 5Y3 last night as I was playing quietly.

Any idea as to the culprit??

I'm taking it in on Moday or Tuesday next week as they can't see it until then anyways (3 Mesa 5Y3's and five fuses in about 7 weeks!). Mesa insisted when I called them about two weeks ago that it was a bad batch of tubes, so I replaced the power tubes with new Mesa's, and put a 3rd Mesa 5Y3 in, which blew last night. Funny thing is, when I put a new fuse in and tunred the amp on (in standby, it turned on, but there was no sound, and the Mesa 5Y3 didn't light up at all. It remained cold. I put the Sovtek, and it lights up, and there is sound. For now, I'm running a Sovtek 5Y3 in it, and it's holding up.

Any thoughts are appreciated.

 

[Chester]

Channel changing pops are apparently normal when in Class A. Happens on my MKV in 10W mode, and is explained in the manual

Less audible on my LSC in 10W mode though

Not sure if your tube issues are nescessarily connected to the pop question

 

[Jared Purdy]

Thanks Chester. I can't be sure either. There are a couple of people (one here, one over at the Music Electronics Forum) who have what appears to be the same issue(s). The one here seems to have had the problem fixed, and what they had to do was quite dramatic, but then his amp is three years old and apparently amps within the serial numbers up to the 004000 range had this problem. Apparently they fixed it after that. The serial number on my amp is around 005300.

I don't know what it is that Mesa changed in the LSS after that, but "apparently it fixed the problem, and I'm not even sure that the pop is related to blowing fuses and rectifiers. I think maybe not, as you have explained it's the same with your amp, and I'm assuming that you're not blowing rectifier tubes??

 

[screamingdaisy]

My LSS pops if I switch between 5w and 15w, so I don't switch between 5w and 15w.

 

[Vogelsong]

I think our supposed to switch to standby before changing the watt switch. I run my LSS at 30 on channlel 1 and 5 on channel 2. I get a weird switching sound when switching channels. I assume this is because the amp is going from using the rec tube to not using the rec tube.

 

[screamingdaisy]

I think our supposed to switch to standby before changing the watt switch. I run my LSS at 30 on channlel 1 and 5 on channel 2. I get a weird switching sound when switching channels. I assume this is because the amp is going from using the rec tube to not using the rec tube.

Going from using 4 power tubes to using 1 power tube in class A with another power tube acting to balance the output transformer somehow.

 

[Vogelsong]

I think our supposed to switch to standby before changing the watt switch. I run my LSS at 30 on channlel 1 and 5 on channel 2. I get a weird switching sound when switching channels. I assume this is because the amp is going from using the rec tube to not using the rec tube.

Going from using 4 power tubes to using 1 power tube in class A with another power tube acting to balance the output transformer somehow.

I figured it was something along that line.

Thanks. Is this something that can be hard on the amp. Playing in two different watts and switching all the time.

 

[screamingdaisy]

I figured it was something along that line.

Thanks. Is this something that can be hard on the amp. Playing in two different watts and switching all the time.

Don't know. What I got out of the manual is that they figured most people gigging would switch between 15 and 30 and added 5w as a 'bonus' for home/studio use, so it wasn't really intended to be switched in and out of all the time. Still, the manual doesn't say it'll hurt anything, just that it'll pop when going in and out of 5w mode.

 

[ja22y]

I don't know what it is that Mesa changed in the LSS after that, but "apparently it fixed the problem,

They remove 2 resistors to make the tubes run slightly less hot. Your tech should be able to verify this when he has the amp open. Also ask the tech to measure the screen grid resistors on the power board. If any of them drifted down to a lower value then replace all of them, there are 5. Mesa for some reason use 1/4 W here where they need to be 1W minimum. When these failed they will take out the power tubes, and then some. On mine this caused the tube to red plated and those resistors just crumbled to pieces when I try to remove them. Check the pwr tube biasing as well. These thing biased extremely hot so make sure you replace them with 'cold or low draw' rating tube.

 

[Jared Purdy]

I don't know what it is that Mesa changed in the LSS after that, but "apparently it fixed the problem,

They remove 2 resistors to make the tubes run slightly less hot. Your tech should be able to verify this when he has the amp open. Also ask the tech to measure the screen grid resistors on the power board. If any of them drifted down to a lower value then replace all of them, there are 5. Mesa for some reason use 1/4 W here where they need to be 1W minimum. When these failed they will take out the power tubes, and then some. On mine this caused the tube to red plated and those resistors just crumbled to pieces when I try to remove them. Check the pwr tube biasing as well. These thing biased extremely hot so make sure you replace them with 'cold or low draw' rating tube.

Thanks, will do. How old is your amp?

 

[ja22y]

I don't know what it is that Mesa changed in the LSS after that, but "apparently it fixed the problem,

They remove 2 resistors to make the tubes run slightly less hot. Your tech should be able to verify this when he has the amp open. Also ask the tech to measure the screen grid resistors on the power board. If any of them drifted down to a lower value then replace all of them, there are 5. Mesa for some reason use 1/4 W here where they need to be 1W minimum. When these failed they will take out the power tubes, and then some. On mine this caused the tube to red plated and those resistors just crumbled to pieces when I try to remove them. Check the pwr tube biasing as well. These thing biased extremely hot so make sure you replace them with 'cold or low draw' rating tube.

Thanks, will do. How old is your amp?

2008 I think, not that old but it was the pre-fixed ones.