#1
I was at the guitar shop a couple of days ago and the guy working there asked me if I heated up the tubes for my amp. (Fender BDR) I wasn't exactly sure what he meant by this but he said that Fender sets the setting to cold so that the stock tubes will last longer. He advised me to turn up the heat, which could get a better tone by bringing the amp to an amp tech. Though he did say that when I would have spent money on my guitar for new strings etc. I should put money aside for the amp.

Does anyone really know what he means by this? And will it bust the warrantee on the amp?
#2
'Cold' means that they set the bias current lower. Setting the current higher supposedly gets 'better tone'. Tone is somewhat subjective so whether that is something you will want to do is completely up to you. Some people hate cold biased amps, some are quite happy with them.

As for the warrany, I don't know. I did some searching on the Fender website and couldn't find any warranty information beyond the length of the warranty. I have a Carvin V3 and I know that setting the bias greater than the Carvin approved bias voids the warranty, but that is a different company, so it could go either way.
#3
To be clear, he's not talking about physical heat. It's just a bias pot adjustment.

You can learn how to bias the amp yourself, I'm sure there are a million guides online for your amp. All you need is a multimeter and a screwdriver, and then you can do it yourself for the rest of your life. You'll need to rebias when you get new power tubes anyway, might as well learn now. Google 'biasing a BDR' or something similar.

Anyway, yes, Fender sets the bias low but there's no need to go to a tech. You can do it yourself and it won't void your warranty.
#4
Alright, thanks for the answers. In truth, does it affect the tone a lot in general? if so how?
#5
Carvin's MTS series amps really came to life when you set the bias hotter, and I've heard that the same is true for their V3 amps. It is likely true for a lot of different amplifiers. If you're into heavy music, it might well be the way to go. Just make sure you don't overdo it. Tubes are expensive.
"Maybe this world is another planet's hell?" - Aldous Huxley
#6
Quote by Wicer
Alright, thanks for the answers. In truth, does it affect the tone a lot in general? if so how?


It really depends on how the amp is before the adjustment. If it's really cold it can make a difference. It just adds a bit of "warmth" to the sound.
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#7
As others have said, a bias adjustment is really quite easy. You can go to Radio Shack and get a good multimeter and you're set.

The hot/cold bias can have a profound affect on the tone your amp provides. Tubes that are not biased properly, underbiased or "cold", will tend to sound sterile. The reason is that at that low current level, the tubes will not produce their full part of the sine wave. That will cause what are called odd order harmonics which are not pleasant to the human ear. Tubes biased slightly "cooler" will have longer tube life however.

When you bias an amp hot, the tubes are pulling more current. This results in an amp that is more dynamic, more responsive and producing the more pleasant sounding even order harmonics. This will shorten the life of your tubes a bit, but the increase in tonal quality may be worth it.

You will want to find out how much current you can safely bias to. You bias outside that and you will have some problems. Offhand, I don't really know what the bias limit would be on those amps.
#8
Don't bother. I change power tubes once (KT88s and EL34s) in this clip and adjust the bias between cold, optimum and super hot for each. See if you can pick each out.

https://dl.dropboxusercontent.com/u/8021347/t00bz.mp3

Amp is dimed as well, which is where you'll hear most differences between power tubes.
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Last edited by mmolteratx at Jul 3, 2013,
#9
In regards to the power tubes, I can't tell you how many people would want their amp retubed with different power tubes, play at low volumes, and then complain it doesn't sound any different. I started handing out a pamphlet that said that power tube distortion kicked in when the amp was played loud, like above 5 on the volume loud. I love KT88s, but they are some big tubes.
#10
Quote by Fenderexpx50
In regards to the power tubes, I can't tell you how many people would want their amp retubed with different power tubes, play at low volumes, and then complain it doesn't sound any different. I started handing out a pamphlet that said that power tube distortion kicked in when the amp was played loud, like above 5 on the volume loud. I love KT88s, but they are some big tubes.


The master volume is at 10 in that clip, attenuated to -12dB and mic'd with a Senn e609 off center. As a EE, and a guy who's worked on a fairly sizeable number of amps, swapping power tubes is pointless when there are 100 other things that have a bigger effect on your tone. Preamp tubes are somewhat worth it, as the interelectrode capacitances can shape the high end content through the Miller effect (which isn't significant in pentodes), but it's diminishing returns for anything but V1. Only reason to spend big money on power tubes is if your amp has stupid high plate voltages and needs SEDs or NOS American/European tubes. Stuff like old Bogners (my 100B has 560V on the plate), Camerons (my CCV had just under 600V ), Jose mods, etc. Other manufacturers tubes just can't handle those voltages.

EDIT: And FWIW, a push-pull class A/B amp will never produce even order harmonics (in theory) and will only produce inaudible levels of even order harmonics in practice. The very nature of a push-pull circuit cancels them out.
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Last edited by mmolteratx at Jul 3, 2013,
#11
Quote by mmolteratx
The master volume is at 10 in that clip, attenuated to -12dB and mic'd with a Senn e609 off center. As a EE, and a guy who's worked on a fairly sizeable number of amps, swapping power tubes is pointless when there are 100 other things that have a bigger effect on your tone. Preamp tubes are somewhat worth it, as the interelectrode capacitances can shape the high end content through the Miller effect (which isn't significant in pentodes), but it's diminishing returns for anything but V1. Only reason to spend big money on power tubes is if your amp has stupid high plate voltages and needs SEDs or NOS American/European tubes. Stuff like old Bogners (my 100B has 560V on the plate), Camerons (my CCV had just under 600V ), Jose mods, etc. Other manufacturers tubes just can't handle those voltages.

EDIT: And FWIW, a push-pull class A/B amp will never produce even order harmonics (in theory) and will only produce inaudible levels of even order harmonics in practice. The very nature of a push-pull circuit cancels them out.


I've seen a lot of stuff regarding the harmonics amplifiers can produce. There are some pretty crazy ones out there, like relativity type ones. I like simple and to me, your explanation makes more sense than any of that other stuff I've read. I need to read up more on that stuff though. I can do the work, but since it's been so long, I really need to get back into that. I've seen some really crazy ones, ones that make my mind spin a bit. Sort of like trying to think about what could be causing time to slow down and human perception of time stopping all together.
#12
It's not a "theory" per se, in that it's fact that a push-pull amplifier has a symmetric transfer curve, which means any and all even order harmonics cancel each other out. It's possible to make an asymmetric push-pull amplifier, where it can generate even order harmonics, but it doesn't sound very good. Peavey holds a patent on what is essentially a limited range volume control for one half of the amplifier, which lets you dial it in as designed, or for more asymmetry. That's what the texture control is on the Valve King, and last I checked, the vast majority of users left it all the way to the symmetrical side of things.

All even order harmonics generated in a traditional guitar amp come from the preamp, as all of the stages (at least in 99% of amps I've seen) are single ended class A stages, which can generate fairly significant even order harmonics (and more upper harmonics, which is why without correct high end filtering, preamp distortion is usually defined as "buzzy"). The funny thing is most guitarists associate even order harmonics with power tube distortion and odd order harmonics with preamp distortion, when in reality it's the exact opposite. The "bark" and aggression that a lot of people describe power tube distortion as having is all odd order harmonics. Also associated with that sound is speaker distortion and how we hear things at louder volumes, but that's a completely different discussion.
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#13
Alright, I have no problem learning how to do this. I'm just wondering if it will affect the tone at a marginally-louder-than-bedroom level?
#14
The salesman is right, companies do ship colder amps. Since you won't be doing this yourself, there's no need to go into how it's done. Just bring it in to a tech tell him about what the salesman said and ask the tech to adjust the bias according.

If you had Weber Bias-Rite you could make adjustments yourself but I don't think these are made anymore.


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Last edited by Gutch220 at Jul 4, 2013,
#15
Quote by Wicer
Alright, I have no problem learning how to do this. I'm just wondering if it will affect the tone at a marginally-louder-than-bedroom level?


Nope. If you can stand to be in the same room as a Fender amp without hearing protection it isn’t loud enough for the power tubes to matter much.