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On the premise that there are no stupid questions! I feel that it is time to change valves in my old Marshall 4210 combo. It has 5 AX7's and 2 EL34's. I bought a set online, (JJ's) and plugged them in. Everything works OK, but now I am worried that I need to have the bias checked before I take it out to a gig. I hear of people changing valves all the time, surely they are not having a tech re bias the amp everytime? And having read how complicated it is for a non electrical type, there cannot be that many guitarists out there who can just casually do this every 5 minutes. I understand the need for this if you are changing valve type (EL34 to 6L6 for example), but just to install a replacement set of EL34's?
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about as important as having your wheels aligned. -
Bias is like giving your car a tune up. Proper bias allows your tubes to perform at their best (tone here) and prevent pre-mature burn out if the bias is too high for the tubes installed. Bias and plate voltage should be checked.Tone is like Art: Your opinion is valid. Listen, learn, have fun, draw your own conclusions.Comment
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Every tube is different. If your amp isn't biased it can cause the tubes to die faster, put stress on the amplifier, or (worst case) burn up the amplifier.
My amp has a bias adjustment knob and some test leads on the back, so I don't need to worry about opening up the amp and electrocuting myself.
Taking the amp to a tech every year or so is not so hard to believe. Plus, the tech might catch a problem that hasn't shown itself yet.
I agree with you that lots of guitarists don't bias their amps on every tube change. And if you're replacing the tubes with the same brand and model, chances are that it's close enough to not need an adjustment.
Dreamland_Rebel said it pretty well. If you don't align the wheels on your car, you wear out your tires faster/unevenly. Is it going to make the wheels fall off if you don't do it? No, but your car will run better.ScottComment
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i love my mts - there is a biasing bay right back there on the back of the amp.
it's very handy, and saves tons of dough.198? Charvel Model 2B s/n 245085
1987 Charvel Model 6 s/n C707218
2001 SL2H Black Pearl s/n U09404
2006 SL2HT Burnt Cherry Sunburst s/n U18151
2008 USA C/S Soloist Soft Arch Carved Top Tiger Eye JA0510
2009 Adrian Smith Dinky s/n 006666 (Ebony Fretboard)
2009 Adrian Smith Dinky s/n 007066 (Maple Freboard)Comment
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My previous amp had external bias points. As an experiment, I tried biasing it very hot and very cold. It only started to sound bad (to my ears) when the bias was ridiculously cold.
From a auditory standpoint, I didnt' hear much difference. From a tube/amp life view, I am sure biasing correctly helps
ymmv"Yes,..that's when they used to shove a red hot spike in your peehole until you screamed "yes, yes, godammit ..you fuggin' dicks..I'm a witch..I am witch..you cocksuckers"" horns666Comment
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If you can use a meter you can do it. theres some good how to's on youtube.Comment
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Well actually just the same brand and model doesn't mean much. You can use new tubes without rebaising if you order tubes that are matched to the same values than the tubes that were in. I've got two amps running on EL34's and both have winged C's in them. But both sets differ quite a bit, they are just matched within the set.Originally posted by Spivonious View Post
But it never hurts to check the bias setting either way. And with tubes with different values than the old ones, biasing is a must.
FloComment
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From my experience there is an effect on tone, but it´s pretty subtle unless you are coming from the extremes of the bias range where you might encounter thin or mushy tone... but mainly I think it´s done for durability issues. I usually bypass the trouble by ordering tubes rated for the same bias, since I have settled on Winged C EL34´s.Comment
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The perception of tone related to bias is different with various amp designs.Originally posted by Dave L View Post
Best to adjust it with the best clean tone in mind, then the drive channel to taste.
Clean sounding amps (like vintage Fenders, etc) get really touchy with the adjustments.Comment
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When I had a 6505+, I had to take it to a tech to have a pot replaced. I asked him about checking the bias/making it adjustable (the 6505+ is fixed bias and it had the stock tubes), and he basically told me it wasn't necessary even when I changed the power tubes, as long as I used the same tube type with the same rating. His reasoning was that the amp got most of its tone from the preamp anyway and if the amp was running fine (no audible issues), there was no need to mess with it. I can see his point and this guy wasn't a hack, so I think there is some truth to this.
Having said that, I owned a single Rectifier a while back that I had bias modded. After putting in new tubes and having the mod done, the amp sounded a bit warmer to me (I was using EL34's). I don't know if it was a mental thing or an actual tonal improvement, but I did notice something. Actually, it was the best sounding Recto I've owned (single, dual, Roadster), and the only one I had modded. I wish I would have kept it.
I also had a Marshall DSL50 for a while and that one was pretty sensitive to bias adjustments as well. DSL's have test points on the back so you can make adjustments easily. Of course, I was aiming for more of a classic poweramp distortion sound with it.Comment
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This could very well be the truth, I have to admit that I´ve only been truly serious with the bias since I got my first Rivera back in ´02... and the only amp I´ve bought since then is another Rivera. So other makes of amp might respond differently to bias adjustments. I guess it was pretty natural to do a bit of testing with the bias once I had amps that were so obviously picky with tubes.Originally posted by Cygnus X1 View PostComment
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kh,
with all due respect to your tech...sometimes the worst advice comes from people that do it for a living. I'm not sure why this is, but it's true.
That's why it's great to learn how to do the minor tech work oneself.
HTH.Comment
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I have a question...the manual for my amp says to adjust the bias to .600V for EL34s, and .450V for 6L6s.
Could this be right? Wouldn't the correct value depend on plate voltages and all that jazz?ScottComment
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True, my Dad always told me mechanics have the junkiest cars because they know how far they can let something slide before it becomes a real problem.Originally posted by Cygnus X1 View PostComment
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