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Post subject: What´s the difference? 6L6/5881 vs 6L6WXT?
Posted: Thu Jan 14, 2010 2:42 pm
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Hi, (excuse my ignorance) The 6L6 tubes of my Fender amp died 2 months ago, after 15 years of running flawless.
In my hurry a friend who "supposedly knows about tubes" replaced with 6L6/5881 (pair) as the manual specifies, I think they were not new, I noticed those tubes were a bit thinner than the original ones and didn´t glow in blue as much, one of them blew after just 2 months.

Went to a real amp technician and did a full service on my HRDX and replaced with 6L6/WXT, those look exactly like the Fender original ones my amp had. And sound real loud and warm (they´re new). The tech guy said those were the ones my amp should use.

So my obvious question is: what´s the differnce between them? Why if the specifications say clearly to replace with 6L6/5881 then why the 6L6/WXT are the "real" replacements for my amp?, why are the WXT fatter?
The only thing I kind of understood, the tech guy told me is that the 5881´s I had replaced with were 4 other purposes.

Thanx and hope someone can clarify.


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Post subject:
Posted: Thu Jan 14, 2010 3:33 pm
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Good question, here's a little something that might help. This was taken from Myles Rose web site "guitaramplifierblueprinting".

Sovtek 5881/5881WXT
This is the industry standard which is fitted as standard by Fender, Marshall and Boogie.
The valve a warm tone but lacks sound stage or harmonic detail of the R.C.A.

When pushed hard tends to go lose control and can sound muddy. The fine detail was blurred compared to other
valves especially with the J.B.L loaded twin. The Sovteks Performed very well on the Microphony test. Only a few
Valves failed the burn in test.

Sovtek 6L6WXT PLUS
The valve differs from the 5881 by having larger plate dimensions and improved grids to allow higher power
handling. The valve performed very well in the microphonic tests and has more top end clarity than The 5881. Mid
range was still muffled when pushed . Bass response was the same as the 5881 soft and sweet. In the Boogie and
Twins we noticed a little more detail and clarity than the 5881. This, however, was not as good as the majority of
other valves in this test in the clarity department.



As far as why one of the 6l6/5881's blew, well you did mention that they looked used so this may have contributed to it's demise. Also, if the amp was not biased after your friend installed them that might have had something to do with why one of them blew too. If the tubes are not biased correctly you may have too much voltage going to the plates which would have also contributed to it's demise.

Normally after all the power tubes have been replaced, as part of a full service, the amp tech will bias them correctly. This would account for the increased in volume and warm sound you got after you had yours serviced.

Hope this helped.

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Post subject:
Posted: Thu Jan 14, 2010 3:34 pm
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5881's are more like the 6L6GB, meaning they break up a little earlier. How they sound tonally really depends on the amp, and what brand tube. I originally had 5881's in my HRDlx and they sounded horrible when they were pushed. They were thin and shrill sounding. The ole icepick in the forehead. I replace d the with JJ 6l6's and it warmed the amp up quite a bit. The problem is the 5881's are usually pretty robust and will sound bad for a really long time. Did you check the bias on the amp after the tube swap? If the bias was set too high (under biased) it would smoke the tubes pretty quickly.


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Post subject: Not to trust always our "expert guitar buddies" ??
Posted: Thu Jan 14, 2010 5:24 pm
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Thanx 4 your quick and informative responses, fender323 and Supro.

Well, definetly my "supposedly expert guitar buddy" screwed up!, (pardon the french), just changing the tubes without biasing. Definetely that xplains why the 5581 got burnt. "DONKEY "me for trusting him!!!....
If I had known all about this before!, It would´ve avoided me the trouble and some bucks. Fortunately, nothing got damaged and the amp is at 100%. with the new tubes/service

(A couple of knobs feel stiffer after the "service" wonder if it´s normal)

Now, in "easy" terms, a WXT is like an improved version of the classic 5881, right?, like 5881 with little turbo?
And I understand clearly I can replace with 5881´s as long as it´s biased by a qualified techinician.

Love the sight of the blue cascade of electrons? flowing down inside the new tubes.


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Posted: Thu Jan 14, 2010 6:41 pm
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"Love the sight of the blue cascade of electrons? flowing down inside the new tubes."

I agree, I wish more manufactures would consider incorporating the asthetic beauty of the vacuum tube into the design of the heads and combo amps, kind of like Hughes and Kettner.

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