Tube Noob Questions

[IndyWS6]

I have a rack rig with a Mesa Simul 2-90 and also a Hughes & Kettner Switchblade head and would like to have some spare tubes on hand in case something goes pfffffft during a gig. If I understand it correctly, both of these amps have fixed bias circuits. I assume that Mesa and H&K both sell tubes that are tested to work correctly in their amps without need for technician intervention. True? If I don't want to buy the tubes from either dealer, what do I look for in terms of the tube rating? For example, if a forum menber has tubes for sale, how would I know that I can safely run that particular tube in either amp? I see tubes for sale here much cheaper than the quotes I get from Mesa or H&K and I assume that there is some "snake oil" in their claims that you need their tubes, or that their's are superior...

* The Mesa uses (8) 6L6 tubes - do I need 2 matched quads since each quad is used for a side (L/R)? According to the manual, it also uses (2) 12AX7 tubes. Are these inside the chassis - they aren't visible from the outside...

* The H&K uses (4) EL34 - I assume that I just need a matched quad...

* Preamp tubes can be swapped without any need for biasing, correct?

Just to head off the inevitable questions and warnings: I am a reasonably smart individual but I am not an electrical engineer. I understand tube amps and circuits from a 50,000 foot view, but I don't know enough to try and do any biasing work, especially on an amp that has no provisions to make this easy. Consequently, I have no intention of sticking my hands in either amp - electrocution is not the last item on my bucket list. Given that these are fixed bias amps, my assumption is that, with the right tubes, I can safely swap them without need for biasing. If that is incorrect, please let me know...

Thanks

 

[just42dave]

it varies for my mesas
I use el34 with 29-35 ratings and check the bias to keep under 32/33 ma
with a bias rite. 6l6 a lil lower but around same range ... 12ax7 i use whatever sounds good..

 

[university81]

allo,

sounds like you're going to have a hefty tube bill incoming =)

Mesa are fixed bias usually (definitely for the heads not so sure on their rack gear), for the power amp, two matched quads for each side , the 2 12ax7s are driver tubes i guess and will be within the chassis,

mesa sell graded tubes, but they are just rebranded mesa labelled tubes, you'll save some money asking a tube seller (doug's tubes..the tube store etc..) to just sell you matched tubes for that piece of gear, if you're going to also buy a replacement set for the switchblade, you can maybe get some kind of discount too

tubes like amps and cables and effects are a matter of taste, they do influence the sound, for the money i like JJs, my experience with them has been good, reliable tubes and they sound decent to my ears, (but other people really don't like them..say they're dark muffled etc..) again depends on the ears, and also which amp you put them in

for the H&K you'll need a matched quad, and a set of preamp tubes,

best thing would be to talk to the place ordering the tubes, to specify the amp and what tubes you need, they might have some good suggestions as well

preamp tubes are plug and play, and power tubes to perform at their best should be biased, on some amps this is very easy to do by yourself, others can be a bit more complicated (amp out of the chassis etc..)

good luck

I have a rack rig with a Mesa Simul 2-90 and also a Hughes & Kettner Switchblade head and would like to have some spare tubes on hand in case something goes pfffffft during a gig. If I understand it correctly, both of these amps have fixed bias circuits. I assume that Mesa and H&K both sell tubes that are tested to work correctly in their amps without need for technician intervention. True? If I don't want to buy the tubes from either dealer, what do I look for in terms of the tube rating? For example, if a forum menber has tubes for sale, how would I know that I can safely run that particular tube in either amp? I see tubes for sale here much cheaper than the quotes I get from Mesa or H&K and I assume that there is some "snake oil" in their claims that you need their tubes, or that their's are superior...

* The Mesa uses (8) 6L6 tubes - do I need 2 matched quads since each quad is used for a side (L/R)? According to the manual, it also uses (2) 12AX7 tubes. Are these inside the chassis - they aren't visible from the outside...

* The H&K uses (4) EL34 - I assume that I just need a matched quad...

* Preamp tubes can be swapped without any need for biasing, correct?

Just to head off the inevitable questions and warnings: I am a reasonably smart individual but I am not an electrical engineer. I understand tube amps and circuits from a 50,000 foot view, but I don't know enough to try and do any biasing work, especially on an amp that has no provisions to make this easy. Consequently, I have no intention of sticking my hands in either amp - electrocution is not the last item on my bucket list. Given that these are fixed bias amps, my assumption is that, with the right tubes, I can safely swap them without need for biasing. If that is incorrect, please let me know...

Thanks

 

[IndyWS6]

I guess what's throwing me is that both of these amps are referred to as having "fixed bias" circuits and the manufacturer's say that biasing is not required.

My assumption is that this only works safely for the manufacturer (to avoid issues and warranty claims) by setting things from the factory on the cold side. That way, you could put nearly any replacement tube in, within reason, without risking damage to other components. I also assume that the tubes that I would get from Mesa or H&K are matched within a range that they know will work properly the way that the amp is built. If, in fact, the assumptions are accurate, what should I look for if I decide to buy power tubes from someone other than the manufacturer? Do tubes vary enough that I need to look for something in a specific range, or are these circuits "plug & play" to the point that I don't have to worry about it?

I realize that I could likely get more out of the amps by trying different tubes and biasing to different levels, but the drunks in the bars that we play certainly won't hear the difference

P.S. Thanks for the help...

P.P.S. - Laura, feel free to chime in. I'm going to need to buy some spares

 

[university81]

the Switchblade has TSC or something no?

"According to H&K, TSC is a comprehensive system that eliminates all the pragmatic drawbacks of gigging with a tube guitar amp. For starters, the amp not only automatically bias-adjusts, but it does so dynamically to compensate for a tube's naturally decaying characteristics over the course of its lifetime.
"

mesa boogie have different graded matched power tubes, whereby depending what colour set you put in the bias range will be automagically set differently (yellow ...red etc.), but the same can be achieved from other tube manufacturers too, usually the place selling you the tubes can do this testing to sell you a graded set for a mesa amp (for either hotter/cooler bias from the fixed bias circuit)

i look for reliability and tone when buying tubes, usually buy them from the same place, the actual brand is of less concern, if they sound good and last =)

I guess what's throwing me is that both of these amps are referred to as having "fixed bias" circuits and the manufacturer's say that biasing is not required.

My assumption is that this only works safely for the manufacturer (to avoid issues and warranty claims) by setting things from the factory on the cold side. That way, you could put nearly any replacement tube in, within reason, without risking damage to other components. I also assume that the tubes that I would get from Mesa or H&K are matched within a range that they know will work properly the way that the amp is built. If, in fact, the assumptions are accurate, what should I look for if I decide to buy power tubes from someone other than the manufacturer? Do tubes vary enough that I need to look for something in a specific range, or are these circuits "plug & play" to the point that I don't have to worry about it?

I realize that I could likely get more out of the amps by trying different tubes and biasing to different levels, but the drunks in the bars that we play certainly won't hear the difference

P.S. Thanks for the help...

P.P.S. - Laura, feel free to chime in. I'm going to need to buy some spares

 

[IndyWS6]

My Switchblade is older and does not have the TSC function...