Sending Amp to Factory for Checkup, Bad Idea?

[dmt]

I spoke to Mike B at Mesa about having him take a look at my amp, give it good run down, and make sure the Saratov KT66 tubes I am re-tubing it with run within the Bias spec. I should have the tubes Tuesday, and can send the amp out the day after.

I am a bit worired that my amp may get damaged getting shipped back due to several threads I read here about how poorly Mesa packs stuff. I really want to have someone who knows what they're doing look over the amp and make sure its running the way it should and find out why the tubes are redplating in Class A mode.

The tech at the Mesa Hollywood store checked the grid resistors when they retubed last year, and supposedly gave the amp a clean bill of health, but the tubes cherry in Class A mode, and it seems that the bias is off. The two tubes directly over the fan (right most) glow brighter than the other two.

Is it worth the extra risk and money to send it to Boogie? What is the chance that Mike B will actually examine the amp and address these problems? I really think that there is something wrong (maybe some components got cooked and are out of spec) and I want the amp in good health. I also want my amp to get shipped back properly packed.

Comments?

 

[MrMarkIII]

"... The two tubes directly over the fan (right most) glow brighter than the other two... "
If you have four power tubes, they run in pairs, arranged thusly: A,B,B,A.
So, one tube of the outer pair (Class A), and one tube of the inner pair is red-plating?

 

[boogietone]

I sent a MKIII in the Mesa about a year and a half. Mike B. gave it a check up, changed a couple caps/resistors and sent it back with no problems. Packing was fine. Amp sounded fantastic. Thinking about sending my MKIV in. It was built in 1992...I think.

 

[phyrexia]

stuff they send back to my job gets packed the same way it does when it arrives new.

 

[jvk]

I don't have any experience with shipping amps back and forth with Mesa, only spare parts, and I've yet to experience any problems.

Does Mesa install bias pots on their amps? Never heard of them doing that. If your tubes are too hot / cold for the fixed bias, what will you do? Maybe MB can adjust the bias resistors but I doubt he does that, he'll surely just offer to replace them with a shiny new set of Mesa tubes?

Cheers,
Jonny

 

[dmt]

"... The two tubes directly over the fan (right most) glow brighter than the other two... "
If you have four power tubes, they run in pairs, arranged thusly: A,B,B,A.
So, one tube of the outer pair (Class A), and one tube of the inner pair is red-plating?

No. In class A mode the outer pair redplates, and the on the right (over the fan) is brighter than the other tube in the pair.

In Class AB:
A B (B A)
The tubes in parentheses glow brighter than the other two. Indicative of a mis-bias?

The tubes that are in there now are Sovtek KT66, which are not really 'real' KT66 tubes. They are more or less 6L6 guts in a different bottle. No significant bias issue should arise. The Tubes I am sending are "real" KT66's, or at least modern production equivalents (read: replicas). They should be in spec for the Boogies, since I specifically gave Jon at the tube store the normal bias specs. They really should be just a drop in substitution.

 

[carlosasi]

I sent my Mark IIA in for repair and was completely satisfied with the way it was packaged and shipped. Mike B worked on it and called me several times during the process. I don't know why he was the one working on it, but I was very pleased of course. I am getting ready to send in my Mark III if I can ever stop playing it. Plus the way these boogies are built, I don't know how you could damage them in shipping. If they fell off of a speeding UPS truck and bounced down the road at 100MPH just re tube and you are ready to go.