My roadster eats preamp tubes

[iceman]

I purchased a new roadster back in May (so ~3.5 months ago. On arrival the reverb wasn't working, the store technician replaced the preamp tube and also applied some outstanding "patches" from Mesa for the amp. A few weeks ago I had a preamp tube die on me and last night the reverb preamp tube died. Preamp tube should last a long time, so am I just getting very unlucky and have bad tubes or is there something wrong with the amp that is causing these tubes to fail early? Anybody had similar issues?

 

[fjk1138]

I had the same problem: New Roadster head, everything fine for about 3 months, then one day turned it on and it would not play. V1 was the culprit on mine, but like you, I would have thought this would have lasted at least 6 mos (or more).

Needless to say, the tube was under warranty and I got a replacement for nothing, plus I bought 3 spares, and it sounds better than it did when I first bought it. But still, the Triple Rec I had before it had the same tubes from when I bought it new and they lasted 5 years with no problem. I figure I just got lucky there.

Despite all of this, the Roadster is very cool and I am not giving up on it, and tubes can basically die at any moment. If that V1 tube goes bad I will post here again. So in the meantime, I say get yourself some extras, and rock on.

By the way -- what do you mean by "outstanding patches"?

 

[iceman]

With regards to "outstanding patches". I called them patches because I'm a software guy, i.e. after you release a product and you find a bug, a patch is released to update and correct the released product. When I took the amp into the tech he said there was a fix kit for the roadster (maybe some resistor changes? not really sure) available that resolved some issues. I guess a should have asked for more details but I didn't. I had originally looked at a Mark V and had the concern that there could be "bugs" with the early editions. The sales guy said that if that were to happen, Mesa (or the store?) would be able to fix the problem after a purchase. So I assumed something like this occurred to the roadster.

 

[Areola]

sounds like your Roadster is going to have problems with cutting up its gums. I'd advice it to eat items which aren't made of glass

 

[domct203]

The only "patch" I know of is to use only Mesa Chinese or the latest Russian (JJ) 12AX7 in the cathode follower pre-amp positions. These are V3 and V5 in the Roadster.


Dom

Here's the info from the Mesa Memo...


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:

GUITAR AMPS BASS AMPS

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.

Dom