NAD!! With a tube replacement question

[nismofreakish]

Hi guys !

I just bought a new Roadster head and I'm so far a happy man!

Since we're going to gig this weekend, I wanna be ready, knowing what to do if a tube fails. I know my amp is brand new but well, we never know.

Preamp tubes
I know they're more unlikely to fail than powertubes, but still. I already heard that some V position are more sensible than others, that not any 12AX7/ECC83 could fit there due to voltage or whatsoever. I'd like to carry spare preamp tubes but would like to know what to do to avoid damaging my amp. I have a spare kit I bought for my Single recto, but there's an additionnal preamp tube in the Roadster (6 instead of 5), so I don't wanna make any mistake.

Poweramp tubes
Since I only had a 50watters before, now that I have 4 powertubes, how to deal with this? I mean, they go by pairs, aren't they? So must I change automatically the other tube matching with the one that failed? If so, let's say from left to right they're numbered like this 1 2 3 4, how are they paired? #1 with #4 and #2 with #3? And do the "good one" that I put out of the amp is just garbage after that since its mate died?

Rectifier tubes
Do they go by pairs too?

Must I be aware of anything ?

(For the record, I already bought spare fuses)

Thanks a lot you guys! Sorry for asking so many questions

 

[MesaENGR412]

For Preamp tubes, any 12ax7 will work. The likelihood that you have all 6 preamp tubes go out is pretty slim, so if you have a few extra 12ax7's that are known to be good, then you will have enough to make the gig. Obviously, if you do the mix and match preamp concoction approach (mixing and matching different brands of 12ax7's), then I would just get a duplicate set of preamp tubes as a back up, that way you would have a spare of each brand of 12ax7 you use, so that you can troubleshoot and find the tube that has gone south with the same brand that is currently in the amp. I use Mesa pre, power and recto tubes, so, I just carry a few extra 12ax7's (i think I have maybe 2-3) for my heads, and I am good to go.

Power tubes are matched pairs and are sold this way, and if you replace one, you need to replace it's matched tube partner. In all Dual Rectifiers (and most other 4 power tube amps for that matter), they are push pull, with the two outside being one pair, and the two inside being the other pair, so it is a-b-b-a with "a" being matched, and "b" being matched. As for the 5u4GB recto tubes, I do not believe these are "matched" seeing as they are not sold as such, so if one goes bad for some weird reason, you should be ok to just swap one.

Hope this helps. Make sure you read your manual if you haven't yet. It is the best thing you can do to understand the head and it's capabilities. If you don't have it, it can be downloaded from mesaboogie.com for free. Congrats on the new head! Roadsters are beast!

-AJH

 

[screamingdaisy]

I generally stick to Mesa's tubes. I like the way they sound, and it makes replacement pretty straight forward.

My one exception is that I like to stick a TungSol 12AX7 in the V1 of my amps. It's brighter than the relabelled JJs that Mesa is currently using, which tend to make an amp sound dull if you use them in every position.

When it comes to replacing power tubes, it depends on how old/worn they are. For instance, if you install new tubes and have a failure within a few weeks, I'd replace just the failed tube. If the tubes are a year old and one failed, I'd replace the failed tube to get me through the gig and all 4 of them when convenient.

Rectifier tubes are individual and can be replaced as such.

 

[RussB]

I would recommend one or two spare 12AX7's, and a spare pair of power tubes. If a rectifier blows, you can just switch to silicon diode mode...and plenty of spare fuses :wink:

 

[nismofreakish]

Ok! Thx!

 

[nismofreakish]

Guys,

I've been asking myself this nooby question for a while...

Since powertubes work by pairs, is it ok to have two different brands of powertubes? Let's say a tube dies, I replace the pair with the Ruby's I have for spare, so it would be a pair of stock Mesa's and Ruby's in the amp at the same time. Would it be ok? Safe? Would the tone, when playing at 100w, be kind of a mix of both brands?

 

[MrMarkIII]

Copied from the Mesa website. This goes back to 2008, so it may not be relevant today. YMMV, etc.

"SOUND “DROP-OUTS” / INTERMITTENT SIGNAL
One Possible Cause

Most (but not all) Mesa/Boogie amplifiers have one or two “cathode follower” tube
stages in their preamps. Tube selection is CRITICAL in these stages.

Specifically, in a 12AX7 tube used as a “cathode follower”, the voltage difference
between that present at the cathode, as compared with the heater voltage, can be
withstood or tolerated by certain types of tubes, whereas other tubes will fail. The
failure of a “cathode follower“ tube will cause sound dropouts or signal loss.

For the past few years, Mesa has been using two types of 12AX7 tubes: ones
originating in Russia (Sovtek EH), and ones originating in China. The Russian (Sovtek)
tube is NOT reliable as a cathode follower. Of the tubes we are using today (March
2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.

In conclusion, if you are troubleshooting for signal dropout in a Mesa/Boogie amp,
suspect a cathode follower tube, and try replacing it with a Mesa 12AX7 that is marked
as “CHINESE” (silk-screened on the tube itself).

Below is a partial list of Mesa amps and cathode follower tube locations:

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch): V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

ANOTHER POSSIBLE SCENARIO may occur in the “SPONGY” (or on some models,
“TWEED”) power setting: the reduced filament voltage may cause very low output from
a RUSSIAN preamp tube. Again, the recommended fix is to replace the “sagging” tube
with the CHINESE type of Mesa 12AX7 - which are more immune to this type of failure."

 

[fluff191]

Guys,

I've been asking myself this nooby question for a while...

Since powertubes work by pairs, is it ok to have two different brands of powertubes? Let's say a tube dies, I replace the pair with the Ruby's I have for spare, so it would be a pair of stock Mesa's and Ruby's in the amp at the same time. Would it be ok? Safe? Would the tone, when playing at 100w, be kind of a mix of both brands?

As long as the matched pairs are within the bias range of a Mesa, that is totally fine. Hell, in the 2 Channel Recto manual, it even says the pairs can be different ratings (A pair of 'red' rated tubes and a pair of 'yellow' rated tubes). Pretty cool.

 

[nismofreakish]

Ok sweet, thanks!

I'm still wondering though if it could be a way to acheive a different sound, a kind of 50/50 of Mesa's and Ruby's sound.