LSS only works in 30w mode?!?!?

[lucaso777]

While in the middle of a gig the amp crapped out suddenly. The fuse blew. I replaced it but the amp would only work in 30w mode. I ran each tube through the troubleshooting method recommended by MB but the light never went out on the amp on the rectifier or any of the power tubes; and it never showed any signs of crackling or lighting.

I've had to replaced the 5Y3GT tube three times in two years but I'm not sure if the rectifier is the problem since the fuse hasn't blown again and the amp light doesn't go out when I only have the rectifier tube in.

Thoughts???

 

[jmontgomery]

30w mode uses a solid state rectifier instead of the 5Y3. If the amp works fine in 30w mode but not the others then your problem is most likely the rectifier tube.

 

[rfrakes]

Or non MB matched power tubes. They can cause the LSS to go into Runaway and blow fuses, melt wire coatings or cook the transformers. Was the reduction mod done on it?

Ron

 

[Lakeabilene]

I have had all three of Mesa's mods 'reduction mod' on my LSS. Done by Mesa authorized repair Mad Science Works in Raleigh. They are excellent at Mesa service. Over the first 6 years of its life, this amp has burned out over 8 rectifier tubes, all mesa branded. Just burned out another Mesa rectifier tube today. I am going back to NOS rectifier tubes, they have not failed me before in this amp. Bendix 6106 is good, RCA 5Y3GT is good and both can be found on ebay for under $20 if you work at it. I think Mesa was putting NOS rectifier tubes in these at one time coming out of the factory as they knew they are at bleeding edge on the tube specs.

 

[Authorized Boogie]

I have had all three of Mesa's mods 'reduction mod' on my LSS. Done by Mesa authorized repair Mad Science Works in Raleigh. They are excellent at Mesa service. Over the first 6 years of its life, this amp has burned out over 8 rectifier tubes, all mesa branded. Just burned out another Mesa rectifier tube today. I am going back to NOS rectifier tubes, they have not failed me before in this amp. Bendix 6106 is good, RCA 5Y3GT is good and both can be found on ebay for under $20 if you work at it. I think Mesa was putting NOS rectifier tubes in these at one time coming out of the factory as they knew they are at bleeding edge on the tube specs.

The amp was designed at a time when the JAN Phillips 5Y3 were still readily available, which is what the amp shipped with in the beginning. As the supply became harder to acquire in quantity, we had to look for alternatives. Its not the amp...but, unfortunately, the 5Y3 that was available. More recently we've had great experiences with the JJ 5Y3. And, for those who never want to change another rectifier tube in their life, the Weber Copper Cap is an excellent alternative. Thanks!

 

[gordwait]

What are the "Reduction Mods" ?

 

[mikiedreb]

What are the "Reduction Mods" ?

A voltage reduction mod to the rectifier tube circuit. The addition of a resistor (s) to presumably circumvent
the blown rectifier tube issue.
I just had it performed on my LSS during a servicing at the factory in Petaluma.

A year ago I suffered the dreaded blown-fuse/5w-15w no workie syndrome. I replaced the Mesa-branded rec tube
with a NOS Sylvania and all has seemed well. I thought the mod seemed like good additional insurance.....

 

[rfrakes]

Mine was blowing Rec tubes. They suggested a Copper cap SS instead of tube Rec. I haven't had any problem since. My Fender amps have original Rec tubes in them from when I bought them in the 70s. For $2K, I am not sure why this amp is high maintenance. One of the reasons I got rid of the Fender Vibro-King to expensive to keep working.

 

[mixsit]

Rabinnh' mentioned changed tone with his SS rectifier..?
The two threads could pretty much be combined..
So I'm curious. Lots of other amps -Mesa's or other, are getting along pretty well with the current available tube versions..?

One other if I may. Might there be a chance the SS version might result in a bit more clean head room?
I'd try it in a minute' if it did.

 

[mixsit]

Mine was blowing Rec tubes. They suggested a Copper cap SS instead of tube Rec. I haven't had any problem since. My Fender amps have original Rec tubes in them from when I bought them in the 70s. For $2K, I am not sure why this amp is high maintenance. One of the reasons I got rid of the Fender Vibro-King to expensive to keep working.

Interesting. Do you suppose the Vibro-King is a like 'exception in the Fender line up', or again- the modern tube quality' issue?
Thanks