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PreAmp Tubes

iriegnome

iriegnome

Bassstar style
Supporting Member
Nov 23, 2001
11,263
5,574
61
Kenosha, WI 53140
#1
Ok. Here is a mystry to me, but I am sure you guys know - How and when should you change your 12AX7 PreAmp tube? How long do they last and What kind should I use. I have an SWR Bass 750 (Pre-Fender). I have had it since new, about 4 years. I have never changed the tube. I have played on average of about 14 hours a week, traveled 8 states. I know nothing about tubes other than my amp has one.
 
#2
iriegnome said:
Ok. Here is a mystry to me, but I am sure you guys know - How and when should you change your 12AX7 PreAmp tube? How long do they last and What kind should I use. I have an SWR Bass 750 (Pre-Fender). I have had it since new, about 4 years. I have never changed the tube. I have played on average of about 14 hours a week, traveled 8 states. I know nothing about tubes other than my amp has one.
Click to expand...

Check this thread:
http://www.talkbass.com/forum/showthread.php?t=209526

If he still has any of the Matsu's left, those are great 12AX7's.. i have a
few, and they sound amazing, but pretty gain-y.. try a 12AT7 for a bit less gain..

You should change it if it starts to go microphonic, or if it just doesn't sound like it used to (right to your ears).

You can find good deals on the 'bay for 12AX7/12AT7.. i'd go with something solid, like a NOS Sylvania or JAN/Philips, but the best way to tell is to try a few different ones.. you should always have a few on hand.

I've also had good luck with these guys:
http://www.triodeelectronics.com/
 
#3
Typically a 12ax7 tube will last for ten to twenty years and does not need to be changed unless it goes microphonic ( this is all stuff I have read).
I have experimented quite a bit with the tubes in my SWR head. Alot of people claim that one tube in a pre amp does very little to the sound of your head. I disagree, I took my head and speaker cab to a local electronics shop. They let me try out all the 12ax7 tubes that they had. Different brands will give your head a different character (I must note the difference is subtle). The type of tube I originally had in my SWR when I purchased it new was the GT Tesla tube (not sure whats in yours) this tube really brings out the Hi- Fi sound of the amp. For a warmer sound and better gain I went with the Electro Harmonix tube. Experiment with different tubes to see what you come up with.
 
#5
iriegnome said:
Mine has the original GT tube from the factory. I do like the idea of a Warmer tone with better gain. I have, BTW, a SWR Bass 750 that I absolutely love!
Click to expand...

I have heard that the GT Mullard re-issuse is an excellent tube. I have the electroharmonix 12ax7 in my SM-500, and it sounds awsome; it also has hi gain.
 
#8
Psycho Bass Guy said:
A preamp tube should last the LIFE of the amp, even modern ones.
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I think I am leaning more towards believing this than what some of the amp manufacturers are telling us. Maybe they are just promoting business for the tubes that they advertise as part of the makeup of their product. Never the less, it is fun to experiment with them to see if you get a different sound. And I am only refering to the tubes in question. If this is true for all tubes, than my guitar player is insane for spending all that money on tubes every four years or so.
 
#10
Well, for a guitarist, the power tubes usually get pretty hammered, especially if the guy plays with a lot of amp based distortion, and that may well be when they need changing. Some guys just change everything when they need power tubes, either because it is easy, or maybe they don't know better. Regarding tube wear, in a preamp tube, about the only thing that may die with time would be the filament - all the heating and cooling thermal stresses, plus the vibration of being moved can cause a filament to break, taking the tube out. Not that common, but possible . . . . remembering back to the old tube based TV sets, filament failures were responsible for a fairly large percentage of tube changes.

- Tim
 
#11
iriegnome said:
Really! They do not wear at all?
Click to expand...

Preamp tubes DO wear, but it's so insignificant that it doesn't really add up until about 50,000 hours for cheap preamp tubes and 100,000 hours for good ones. Transistors wear out, too, BTW.

seansbrew said:
And I am only refering to the tubes in question. If this is true for all tubes, than my guitar player is insane for spending all that money on tubes every four years or so.
Click to expand...

Power tube life varies ALOT more and depends on more variables like bias, voltages, and even what kind of cabinet you use. If your guitar player is buying new preamp tubes every four years, he's getting taken. If he's buying new power tubes and you guys don't gig four hour sets six times a week every week at death-metal volume, he needs to find a tech who knows how to PROPERLY bias his amp.

iriegnome said:
2 of my 3 guitarists change their tubes about once a year.
Click to expand...

I'll gladly take all their 'pulls.'

The other changes his about every 2 years. Tubes + Tech time to have it biased. CRAZY :hyper: .
Click to expand...

BTW, you ONLY need to have power tubes biased. Preamp tubes are cathode (pretty much self) biasing.
 
#13
I do know that since all 3 of my guitarists are professional Music Teachers, the 2 twins are on at least 8 hours a day at work then 4 hours each practice and 5 to 6 hours each show with setup time and everything. I would estimate the tubes are used about 50 to 60 hours per week. That seems about right. I don't know. I do know that I have had my preamp tube in my amp for 5 years now.
 
#14
I have a SWR Bass750 and have tried a few tubes in it:

GT Mullard clone: Not really good. Too much unclear muddy midrange, and boomy in the bass. Breaks up suddenly instead of gradually.

Ei Elite: Really good. Warm, but still tight. The second best of what I tried.

GT 12AX7A: Had more bass than the others, but nothing special.

Sovtek 12AX7WA: The tube that was in the amp when I bought it (new). Flat and very prominent in the treble. Not much life.

Sovtek 12AX7LP: A little more life than the other Sovtek and a little warmer/complex in the mids.

GE 5751 (NOS) Blackplate: By far the best I've tried, and the one I use now. It's warm and round sounding, yet detailed and airy. Pretty expensive compared to the others, but worth it.


I didn't find the sound changing dramatically with the tubes, but it's definitely a way of perfecting your sound. It's not going to make your SWR sound like an all tube amp or something, but it can change those little differences that matters in the long run, especially the harshness that SWRs are infamed for. If you want a quick cheap fix, get the Ei Elite or of you want to go all the way get something NOS. Alot of SWR owners seems to have had great succes with the 5751 types.

Good luck.
 
#16
I checked out the GE 5751 tube. It is rated at 70% less output. It is also used to limit guitar preamps with too much gain.

The Ei tube is strongly not recommended for use in guitar/bass amplifiers due to microphonic issues.

A Tungsol 12AX7 is the Ultimate 12AX7. Big, warm, and musical. High Gain, ultra-low microphonics, and superb linearity with a dynamic 3-D sound.

GT 12AX7 are popular for it's gain and bite.

The more research I do the more confused I get
 
#19
iriegnome said:
I checked out the GE 5751 tube. It is rated at 70% less output. It is also used to limit guitar preamps with too much gain.

The Ei tube is strongly not recommended for use in guitar/bass amplifiers due to microphonic issues.

A Tungsol 12AX7 is the Ultimate 12AX7. Big, warm, and musical. High Gain, ultra-low microphonics, and superb linearity with a dynamic 3-D sound.

GT 12AX7 are popular for it's gain and bite.

The more research I do the more confused I get
Click to expand...
The Ei warning is old I believe. The one I have had no problems. As for the lower gain in the 5751, it's not really a problem. Just turn the gain knob up a little further.
 
#20
carl-anton said:
The Ei warning is old I believe. The one I have had no problems. As for the lower gain in the 5751, it's not really a problem. Just turn the gain knob up a little further.
Click to expand...
The reason I am looking into changing my tube is that I am loosing gain. So I think that my tube is going bad.
 

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