#1
Hey i replaced 4 of the bigger tubes but i left the smaller ones(power tubes?) is this ok or should i replace all of them?Also i didn't bias them is this ok?They were the normal marshall el34s that come in the amp and i replaced them with electro harmonix.
#2
the small ones are the preamp tubes, and they usually last longer than power tubes. The big ones are power tubes, and those should all be replaced at the same time with a matched set or quad.. If you used the same tubes with matched grade numbers, you don't need to bias it. If not, you should have it biased. Power tubes need biasing, preamp tubes do not.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#4
there will be a brand label, and on some tubes, there will be a series of numbers that isn't related to the type of tube. I've seen them on some EH tubes, where it's just a small 4 digit number. On Mesa tubes, they are graded by color code, so you can buy one tube at a time, but still be assured the tube is matched with the others correctly. The important thing is to have a matched set.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#5
There is 73 written on them by marker is this it?the old ones where 56.Do i need to bias them?Also does it matter where the power tubes go?Like say a certain tube has to go in either slot one or two...it's not like that is it?
Also if i do need to bias will i take out the preamp tubes too?

Thanks very much for your help so far.

Oh wait i think i know the number your on about.I says 0412 under where it says made in russia is that it?
But on the old marshall theres five numbers 00070.
Last edited by mr_fruitbowl at Jun 7, 2006,
#6
yeah, if they are a different brand, you should get them biased, I've only seen it used with the same brand. It doesn't matter what order they go, as long as you bought a "matched" set of power tubes. You don't need to take out the preamp tubes to bias it. If you are not familiar with biasing an amp though, you should take it to a tech. It can be dangerous working inside a tube amp if you don't know what you're doing.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#10
^No. You should always bias tubes. You shouldn't even put them in your amp if you're not sure they match.
#11
I thought the whole point of biasing them is to make sure their the same and im 90% sure they are the same.I bought them in a set of four.I don't have to worry about preamp tubes during all of this do i?
#12
preamp tubes don't need to be biased. You are biasing the amp, to feed a certain current through your tubes. Biasing does nothing to make your tubes more similiar, it's only something you adjust on the amp itself. Matching the tubes assures that they can all be run at the same values together. You have to specify that you want matched tubes when you buy them. Hopefully whoever sold them to you assumed you wanted a matched quad.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#14
right. It's the amp that gets biased, to run your tubes at the optimal values. Vacuum tubes are an old technology. Even tubes from the same company and batch can have different values. When they match them, they test the tubes to find a group that has similiar characteristics and values.

When you bias the amp, you set the amp to run the tubes at a balance between best tone, and longest tube life. Bias it too cold, and it will not sound as good as it can, because you will get crossover distortion. Bias it too hot, and it will sound great, but you will dramatically affect the life of your tubes.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#16
Biasing isnt all that complicated but if you don't know what you are doing then don't try it. Just go down to the shop they should be familiar with the process and they will do it for you and will probably show you how if you want. Ahh, this is the beauty of Mesa amps, no need to bias.