#1
Ok, so I'm looking into buying a Mesa Roadster head, and on the site it says that all Mesa amps have a "Fixed Bias for Consistent, Maintenance Free Performance." Can somebody elaborate on this a bit more please? I'm fairly new to tube amps, but I do know how to change preamp tubes. With this fixed bias, does that mean that I can change the 6L6's in it just like I would the 12AX7's? Also, are the 5U4G rectifier tubes changed the same as the 12AX7's, too?

Thanks
#2
usually when you change tubes (mainly power tubes i believe) you have to "bias" the amp to adjust it to fit the new tubes. apparently all tubes are somewhat different and biasing allows for the adjustment of the amps so you can get the best sound and longest life out of your tubes.

with mesa amps, they don't allow for any biasing of any sort, so basically you can swap tubes over and over again without biasing once and your amp will be ok. some people argue that your not getting the most of your tubes with a "fixed bias" but other argue that the ability to choose and hear a wide variety of tubes without the hassle of bringing your amp to the store for biasing or ever doing it yourself if you know how is great.

as for changing tubes, all you do is pull the old ones out and stick the new ones in, there's nothing complicated about it

the 6L6's are your power tubes, your 12AX7's are the pre-amps tubes, and the 5U4G are the rectifier tubes, each are in their own category and are NOT interchangeable. however, if you buy a new set of 6L6 tubes for instance, you can take the old 6L6's out, put the new ones in and play with them right away.

there's a "tube thread" stickied at the top and they know a hell of a lot more than i do. try there if you have any more questions.
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#3
Quote by Waterboy799

the 6L6's are your power tubes, your 12AX7's are the pre-amps tubes, and the 5U4G are the rectifier tubes, each are in their own category and are NOT interchangeable.


I know they're not interchangeable. I don't own a tube amp, but I know a lot about them. What I meant whas if they were taken in and out of their sockets in the same fashion. Thanks, though.
#4
Quote by LukeBTH
I know they're not interchangeable. I don't own a tube amp, but I know a lot about them. What I meant whas if they were taken in and out of their sockets in the same fashion. Thanks, though.


as far as power tubes and pre-amp tubes go all you have to do is pull them out. as far as rectifier tubes go i don't know because the amp i have doesn't have any rectifier tubes but i can't imagine why it would be any different.
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#5
Quote by Waterboy799
as far as power tubes and pre-amp tubes go all you have to do is pull them out. as far as rectifier tubes go i don't know because the amp i have doesn't have any rectifier tubes but i can't imagine why it would be any different.


Really? You just pull them? On the one "Tech Ed" on one Guitar World disc (I believe it was July 2007, Slash on cover), Matt Bruck said you had to pull them out with a slight twisting motion.
#6
^this is correct. This way you don't break em
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#8
Quote by al112987
This is odd, fixed bias means that the bias DOES need to be set.

there is adjustable fixed bias, and non adjustable fixed bias, Mesa's is just non adjustable.

As with anything, it has it's drawbacks and good points. Mesa sells tubes, so they test their tubes to operate correctly with their fixed bias. They color code the tubes when they match them, so if you blow only 1 tube, you can just match up the color code and replace just the bad one. Normally you have to buy a matched set of tubes. You can also buy from other vendors that know and can test tubes for Mesa's bias, you just have to tell them what tubes the amp is for.

The caveat is, again, you need to buy from a vendor that can test for Mesa's bias. Even with testing and matching, it's a best match scenario. I haven't gotten any sets that tested exactly the same, even matched, they just select ones that are a close match. Certain tubes could be running cold or hot if the variance is far from the others, which can affect sound quality. Also, certain amps can sound better with the tubes running on the hot side or even colder side, so adjustable fixed bias has an advantage there.

Also, there is no twisting to get the tubes out. They are in pins, just like the preamp tubes. You can use a very slight rocking motion to slowly work the tube out, but you don't want to twist or move it too far, otherwise you can bend pins, or break the center key. There is a plastic piece in the center of the pins on power tubes. You use this to orient the tube pins correctly in the socket. There is a ridge running down the key, and it fits the ridge in the center hole in the tube socket.
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Last edited by Erock503 at Aug 12, 2008,
#9
When you get tubes, order from someone like dougstubes or thetubestore.com and when you order you type in what amp the tubes are for and they'll send you ones biased for your amp. Don't get mesa tubes, they're cruddy and overpriced. When you get the power tubes, you pop them out and in just like the preamp tubes, but you must make sure they are in the right order if you have more than 2 tubes. If you have 2 power tubes, just pop them in. If you have 4, you will be ordering two matched pairs. When you get them, the pairs will be marked. You would put them in order like this xyyx so one pair on the outside one on the inside. If you have 6 power tubes, it would be xyzzyx.
#10
Quote by Say Ocean
When you get tubes, order from someone like dougstubes or thetubestore.com and when you order you type in what amp the tubes are for and they'll send you ones biased for your amp. Don't get mesa tubes, they're cruddy and overpriced. When you get the power tubes, you pop them out and in just like the preamp tubes, but you must make sure they are in the right order if you have more than 2 tubes. If you have 2 power tubes, just pop them in. If you have 4, you will be ordering two matched pairs. When you get them, the pairs will be marked. You would put them in order like this xyyx so one pair on the outside one on the inside. If you have 6 power tubes, it would be xyzzyx.

you actually want to order a matched quad, or in your case, a matched sextet. They match all the tubes to be within a certain spec of eachother, so they all draw approx the same plate current. Pairs would only make sense if you had individual bias pots for each pair. Boogie sells them in pairs, but that's because they are color coded, so two pairs with the same color coding is actually a matched quad.
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#11
Quote by Erock503
you actually want to order a matched quad, or in your case, a matched sextet. They match all the tubes to be within a certain spec of eachother, so they all draw approx the same plate current. Pairs would only make sense if you had individual bias pots for each pair. Boogie sells them in pairs, but that's because they are color coded, so two pairs with the same color coding is actually a matched quad.



I never order whole matched quads for my triple rec
#12
Quote by LukeBTH
Really? You just pull them? On the one "Tech Ed" on one Guitar World disc (I believe it was July 2007, Slash on cover), Matt Bruck said you had to pull them out with a slight twisting motion.


hey if a Guitar Tech guy says pull 'em with a slight twisting motion and it works, then why not.

i'm no amp expert i just do whatever seems to work for me at the present time and i haven't broken any tubes yet.

Quote by Erock503


Also, there is no twisting to get the tubes out. They are in pins, just like the preamp tubes. You can use a very slight rocking motion to slowly work the tube out, but you don't want to twist or move it too far, otherwise you can bend pins, or break the center key. There is a plastic piece in the center of the pins on power tubes. You use this to orient the tube pins correctly in the socket. There is a ridge running down the key, and it fits the ridge in the center hole in the tube socket.


yea that's more of the lines of what i was thinking
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#13
Quote by Say Ocean
I never order whole matched quads for my triple rec

if you ordered the kit from Eurotubes, or 6 tubes from doug and told him it was for a triple rec, you did get a matched sextet. It's the same price to order 2 matched pairs or a quad of matched tubes.

Hey man, btw, did you ever try Ruby 6L6 in that amp? I had a 2ch TRec, and I really liked it. I traded it to Keith(dimebag11 from HC), and he's loving it. You know how he is with amps too, lol. I was very impressed with them, and they are pretty cheap too. Just a consideration next time you retube.
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Last edited by Erock503 at Aug 12, 2008,
#14
Quote by Erock503
Also, there is no twisting to get the tubes out. They are in pins, just like the preamp tubes. You can use a very slight rocking motion to slowly work the tube out, but you don't want to twist or move it too far, otherwise you can bend pins, or break the center key. There is a plastic piece in the center of the pins on power tubes. You use this to orient the tube pins correctly in the socket. There is a ridge running down the key, and it fits the ridge in the center hole in the tube socket.


I don't mean twisting it like a light bulb. I mean like the rocking motion that you mentioned, but Matt Bruck said to rock them in a circular pattern.