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Mesa "special requirement" power tubes - long


 
7/6/2000 10:40 PM
Randall Aiken
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Mesa "special requirement" power tubes - long
I was running low on EL84's the other day, and rather than wait for a delivery from my usual mail order sources, I figured I'd run down to the local guitar store and see what they had in stock (yeah, I know better, but I was in a hurry, okay!).  
 
I saw a pile of unboxed Sovtek EL84's, which looked like pulls to me, and a bunch of Mesa boxes. The sales guy came over and asked what I wanted, and I told him I wanted some EL84 tubes. He told me that Mesa's "selected" tubes were the best you could get, and he recommended I buy them.  
 
I told him that most of the people I run with consider the Mesa tubes to be overpriced, relabled versions of the same cheap Chinese and Russian tubes everyone else sells, and I didn't want them. He basically inferred that I was full of it, and he had never heard that before, and these were great tubes, never had any returned, etc. I asked the price, and he said they were the same as the Sovteks (which were nowhere in sight, except for the unboxed ones, which I didn't want to take a chance on), so I figured, what the heck, I'll take a chance on them, since I was in a bit of a hurry. I asked for a matched pair and he told me they didn't offer them in matched pairs, but these were Mesa tubes, after all, and were the best.  
 
Since Mesa doesn't have bias controls in their amps, these have to meet special bias tolerances, right? They are "special requirement power tubes", so they should be well-screened. Well, I put them in my amp and immediately one of them started glowing a bit red on the plates. The other was fine. Also, as I played the amp, I noted that the grids inside would start glowing a bright red as I hit a chord at full volume. Nice.  
 
I measured the bias current (actual plate current), and the cold one was at 27mA, and the hot one was at 48mA! The screen current on the cold one was 3mA, and the screen current on the hot one was 5mA. This was at a plate-to-cathode voltage of around 320VDC. I popped in a set of Sovtek EL84's which biased up properly, and all was well, no glowing plates, no glowing grids.  
 
So what is this "special requirement" anyway? Are they "specially required" to burn your amp up? These tubes could not possibly have gone through any kind of screening process whatsoever. Also, for those of you who think cathode-biased amps need no bias adjustment, take heed!  
 
Randall Aiken
 
7/6/2000 11:18 PM
Frank Clarke
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I got the same uselessly mismatched numbers last week with Mesa Boogie EL84's. I can guess what the "Special Requirement" is. The Mesa 12ax7's were fine but I had to buy 2 because they were "Matched".  
It's unfair for Mesa Boogie to make claims that their amps don't need biasing because of the quality of their tubes.
 
 
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7/6/2000 11:41 PM
Les
Randall, you KNOW better than that... what WERE you thinking fer crissakes... yes, i can understand being in a hurry, and needing something NOW... (like an hour before a gig :D) but you know as well as i do, (if not better than I) that Mesa is so fulla crap that it hurts cuz i'm laughing so hard when i hear some the garbage that spews...  
 
Les
 
7/6/2000 11:59 PM
Peter S
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I'll probably get some heat for this, but here goes....it needs to be said. Mesa tubes are dismally awful garbage. Their amps are a few notches better. I really don't understand what the hype is about Mesa. Last week we were joking in the shop about the poor quality of one of their amps and how miserable they are to work on. someone said they would rather have a Crate amp to work on so we dug one up and cracked it open and sure enough, easier to service(marginally). The really sad part was they both sounded about the same....very very generic. zzzzzzzzzzzz......  
 
Peter S
 
7/7/2000 1:00 AM
John Stokes
Come on guys, we've all been through this before. It's just the sales/marketing hype machine in high gear to sell their overpriced trash to the masses who are basically clueless about this kind of stuff. You get high profile guys like Randy Smith, Pittman, Torres and the like, spewing their crap, and the average Joe Schmoe doesn't know any better and gives them all his cash. It works, they make money.  
 
Randall, you of all people should have known better. Since the tubes are under warranty, have you tried to return them since they are obviously grossly mismatched? It would be interesting to hear what excuse the salesman has. I strongly suspect that Mesa EL84s are not matched at all.  
 
One thing that really gets me is when you go into a music shop and the salesman there, who doesn't know you from Adam, starts in with this load of crap and hype that you know is 110% bullshit, but he believes it to be true. If you try to contradict or correct him, he gets indignant and tells you that he is the professional and you don't know squat. At that point I can barely contain myself so I just leave.  
 
Very frustrating.  
 
There's a music shop down in Sacramento I was browsing in one afternoon. I noticed they were selling GT and Mesa tubes at full list price. for kicks, I asked the sales guy about them and why they were so expensive. The response was something like "GT and Mesa make the best tubes you can buy. All the Pros use them." At that point, after a long pause, I simply thanked him for his time and left the store. "Make"???!!!???  
 
Other than what I heard from Gil, every other Mesa amp I've ever heard sounded like crap.
 
7/7/2000 2:13 AM
Randall Aiken
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Yeah, I did know better, but it was a choice between boxed Mesas and loose Sovteks piled on the bench, and I needed them right then. I figured I'd give them the benefit of the doubt. I was curious to see how good the "Robotube" tester hype was anyway. Looks like pure marketing fluff (yeah, I'm shocked and amazed). I rather suspect these were never tested to any "stringent specification".  
 
This is what their website proclaims:  
 
"Our State of the Art Tube Tester With the brains of a computer and the ears of a musician, Robotube runs a battery of seven exacting tests on each power tube and analyzes performance so thoroughly it can even predict the tube's lifetime."  
 
Wonder what those seven "exacting" tests were, and how long it predicted these EL84's would last? :)  
 
Also, since these weren't sold as a matched pair, I wonder if they will take them back - how can they be out of spec if Mesa publishes no spec on their tubes? How do I know the replacements I get will be any better? I suppose for grins, I'll try returning them to the store I bought them at and see what the sales guy says when I tell them they were too far off in bias current to be able to use them. I guess I could keep taking them back until I get a pair that biases up close enough to not melt down.  
 
It wouldn't bother me if I had bought unmatched tubes from New Sensor, Mojo, Ruby, or any of the other major suppliers. I would have expected them to differ greatly in bias current, and would have paid one-third the price, bought a bunch, and matched them myself, as I would have expected to. These tubes were sold at a high price, supposedly "tested" and fully screened to be able to go into a Mesa amp with no bias adjustment necessary.  
 
FWIW, I picked up a quad of Groove Tubes "#5" EL84 at another store after I found out the Mesas were useless and found they were matched to within 3mA or so. Not too shabby, but the price was still way too high. At least they didn't melt down and the screens didn't glow bright orange.  
 
Randall Aiken
 
7/7/2000 3:35 AM
R.G.
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quote:
"Wonder what those seven "exacting" tests were, and how long it predicted these EL84's would last? :)"
 
I'll take a few guesses:  
 
1. All weigh pretty close to the same; within spec  
2. Height matches  
3. diameter matches  
4. fits an octal base to close tolerances  
5. heater temperature as measured by observed color of light emitted is very close  
6. Electrons go **exactly** the same direction through all of them.  
7. All conduct at least X current when hooked up as diodes (oops - that does tell about cathode emission, so it could conceivably be useful)  
 
What do you think?
 
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