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#1 · (Edited by Moderator)
Pre-amp valve selection! The valves/tubes you choose to use effects your tone in a big way (almost as much as a new pickup!) luckily it doesn't cost as much (unless you have more than 4 preamp valves). It is also 'lucky' that you HAVE to change them. Otherwise you could end up with a tone you hate for the rest of your life! Most people who aren't up on valves think "an 12AX7 is a 12AX7" This is totally wrong! There are many types of ALL valves (EL34s, 6L6s I mean ALL valves). They are normally have a designator, which follows them (e.g. 12AX7-C) This represents different types of tube, It also Represents their origin.

Key:
C- Represents China made Valves
R-Russian
R2-Different Russian factory
S-Formally the Telsa factory now owned by JJ. In the Czech republic
Y-Yugoslavian
GE-USA only Groove tubes use this key (I think)

These are the stock 'codes' for Groove tubes. Although some Dealers advertise all valves this way. I am not going to go into the argument of makes because I am sure I will offend somebody who swears by a certain company.

Also in my personal opinion we shouldn't get too wrapped up in the NOS game (unless you have a vintage amp and lets face it if you can afford a vintage amp you would be able to afford those ridiculous tube prices!) . I know many say that they love Mullards and I agree but it is really risky to buy them! Firstly they cost a bomb more than a set of new valves! Also as they are 'old' it means they weren't used when they were new, This leads me to believe that they were 'duds' in their prime in some cases. So always ask a supplier to test valves before you part with your cash EVEN NEW VALVES! Also you don't know whether NOS tubes have been used or not!! so you could end up with some really old valves that are dead!! Also the original box is a must (all though I believe lots of people make fakes and charge top $$$).

Also despite common belief there is only a small number of tube manufacturers in the world. So a China valve from one company will sound similar to another (although their will be some differences due to different active components used and glass thickness)

Right onto selecting valves. Like choosing pickups you need to know a few things:
1) What type of amp you are using? This is similar to what pickups go with what body woods. But as with pickups some people like weird combos! A 'good' way to determine good combos is to know what tube the amp was designed around (stock tube) because most companies are looking to save money the use the cheapest valves they can get their hands on. So to make up for it they optimise the amp around them to sound better. So a valve from the same origin is considered to be 'right'. Also vintage amps were designed around NOS tubes so those should sound 'right'.
2) What style of music do you play? If you need a lot of headroom a valve with a lower gain rating would be desired (for output tubes a slower break up)
3) This is most important and is the same as choosing a pickup. What is your sound lacking or have too much of?
4) An obvious one. What type/brand of tubes does your amp have in the first place? If you have a REALLY bright set of tubes in there and think it is too bright go down to a medium brightness unless a huge loss is required. Also if it is sounding weird even after the tube change TAKE IT TO A TECH. It will most probably be drifting values of some kind.

Right now that is said lets move on. So the main type of valve (and the most used audio valve of all time!) is the ECC83/12AX7/7025 despite a minorities belief these are the same. The 7025 never used to be though, it started out as a higher grade ECC83 but now most people regard it as the same valve.

Lets start off with the China made these normally have a fair bit of gain. And have a fat warm tone. There are rumours of low quality valves coming from China but I hear the new ones are quite good (hopefully). It also meets the original ECC83 spec very well (almost perfect) so they work well in vintage amps! Although in modern amps (usually designed around Russian valves) it may have too much gain and hum a bit. Although I know a few people who love these in modern amps. Although there is a bad sign over at www.watfordvalves.com which policy states:
"Chinese valves
For the performing Musician and professional audio industry we have found that these items to be lacking in both terms of reliability and performance. Watford Valves therefore cannot recommend fitting such items and as company policy do not stock or offer items of Chinese Manufacture." They also slate their tone and regards it as 'wasp in a jam jar' and fizzy. So they are good for reliability but not for tone!!

Secondly lets look at the good Old Russian valves. (AKA SovtekWA) These are probably the most used in modern amps. Reliability is pretty good with these although not many people like the tone. It is generally lower gain and darker than most other valves on the market. (So maybe good for bright Fenders?) It is also very mid orientated. The balance between the 2 sides of the valves is normally very poor so I wouldn't use them in a phase reverser or driver stage!

The R2 Russian valves seem to be really bright. But can be prone to microphonics. The quality control is meant to be an issue with the Groove tubes though. It has a higher gain than the other sovteks WB.

Sovtek LPS are pretty good too. They are pretty similar to the EH brand tubes but a few people regard them as better because of a flatter freq response. Although I have never had both side by side to compare.

There are also Electro Harmonix Sovteks these are really great valves. Low microphonics and good gain. Also it has a spiralled filament so AC wiring noise is kept to a minimum. It is definitely based around the higher frequencies! Real trebly!!

Next comes the Telsa factory (Czech Republic) . The newer JJs are regarded as some of the best tubes of today. They are also very similar to the Electro Harmonix tubes in sound. It has a huge output much bigger than any other new valve. They are fairly high treble response and is favoured for hard rock and metal. (Especially in high gain amplifiers) These have a very thick glass (on JJs) Also really low microphonics on the new JJ/Telsa's. And a long life. It is clear to see why they are so popular!

Next we have the Yugoslavian tubes. They are immensely bright and biting and may become brittle in Marshall's! But they complement Fenders very well (and early Marshall JTMs which are basically fenders!)

American Brand tubes are always quality! Groove tubes have their GE series, which are great from what I hear but are expensive. Sylvanias are also regarded as great tubes. Very rich and warm sounding. It's a standard rock valve with average gain but cleans up nicely.

Another brand is Svetlana.They are replicas of the Mullards which is a good sign! But are not regarded as top quality by 'audiophiles' I have never had any experience with these so I can't comment.

I am unsure of their origin but the Harma valves have been a favourite of mine. In the USA I think you call them European STRs? Anyway I love these valves! They have a sound reminiscent of the sort after Mullards but are cheaper and easier to get hold of. They are also Brian May's favourite of the new valves. He now uses them in all his AC30s! I am probably going to use these in my amp when it is built.

Also Mesa Boogie now have their own brand tubes. They are said to be the only valves that work in their amps. But they aren't being strictly true ;) Any tubes can work in Mesas fixed Bias amps. It is not that hard to do with either a slight knowledge for amps or a good tech ;) Firstly you need to locate the Bias resistor. And take it out. You then need to replace a trimmer in there. Bias like normal. Get the trust VOM/Multi meter and measure the resistance. Replace the trimmer with a resistor of the same value and you are done! This will only work with valves with good quality control though. Other wise it would all go wrong! There are also numerous mods to install a bias trimmer to mesas you can find them on any good schematic site.

Another thing to add to choosing pre-amp tubes is they are pretty much universal! You can (almost) use any 12xx7 in place of a 12AX7! Why would you do this? For a different sound. It doesn't need any modification to the amp to do this (unlike output tubes.) I am inclined to get a set of 12AY7s for my Marshall DSL. It reduces the preamp gain by over ½! It also makes modern Marshall's to (almost) like the old Plexis! I am just looking for a model that will make it a little darker sounding as well. Then adding fast 'break up' EL84s will make things really scream ;)

The 12AT7: This is usually used in the driver stage section of modern amps, but in Fenders early days was also used in the preamp as well. It has less gain than an ECC83. Another name for the AT is an ECC81. In modern high gain amps it can be used to reduce the gain (and most probably noise).

The 12AY7: It has a tiny amount of gain, which leaves the big distortion up to the power stages ;) It is less than ½ of the gain of the AX. Leading to a lot less noise and a 'cleaner' feel. But it has over double the output! This will really pound your output/power tubes to the compressed saturated distortion! So if you think your amp is too high gain try these!

The 12AU7: It has a tiny gain compared to an AX. Only just over a 1/10!! But the output is almost 10 times as much!! It has huge clean headroom though. Favoured by fingerpickers and adds a softer touch to the tone. Another name for this is the ECC82.

I have hunted around the internet for all these 'reviews' but mostly it is from Watford valves. Also regarding Some of the output and gain info is from the amazingly good book by: Aspen Pitman and is called "The tube amp book".

Class dissmissed :lol:
 
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#28 ·
Mr Orange said:
I'd say, try out stuff.
You'll probably go broke if you "try out" as much stuff as I did. :lol: I'm just trying to share my experience here, that's all. Ultimately, who gives a crap if it's Mullard or Sovtek. Even the most discriminating guitar player (even Eric Johnson :lol:) won't tell one from another in a blind test. I bet Steve doesn't even know what brand of tubes he has in his amps.

Due to time constraints gear tweaking and guitar playing tend to be mutually exclusive, for me at least. Money is also a constraint for some. What I'm trying to say I guess is that "trying out" tubes isn't the best investment one can make, financially or time-wise. The differences are barely noticeable anyway,
 
#29 ·
microdmitry said:
You'll probably go broke if you "try out" as much stuff as I did. :lol:
I'm pretty sure about that as well. I'm struggling, day by day... :wink:

I'm just trying to share my experience here, that's all.
Ditto.

Ultimately, who gives a crap if it's Mullard or Sovtek.
Amen. If it works, it works; even though someone pulled it out of the aforementioned gorilla's butt.

Even the most discriminating guitar player (even Eric Johnson :lol:) won't tell one from another in a blind test. I bet Steve doesn't even know what brand of tubes he has in his amps.
Eric Johnson has tinnitus and is doing acoustic gigs nowadays... :wink:

When it comes to preamp tubes, all I personally care of is that they're not noisy, provide a decent tone and won't die prematurely. And tone, well, that's a subjective matter, as discussed before. I still claim that there are subtle differences.

Money is also a constraint for some.
Count me in.

What I'm trying to say I guess is that "trying out" tubes isn't the best investment one can make, financially or time-wise. The differences are barely noticeable anyway,
That depends on the definition of "trying out". I don't by any means encourage all poor guitar players to go out and spend $1000 on preamp tubes just to try things out. But when changing tubes experimenting with a couple of different brands isn't that lethal to one's psyche, ears, or wallet.

Like I've said before, the amp makes the amp, not the tubes. Yes, the differences are subtle but they do exist. Hey, we bitch about body and neck woods here on this forum as well, so... :lol:
 
#30 ·
Miller Capacitance:

Miller capacitance is a subject that is associated with any tube or transistor. In layman’s terms, it affects the circuit as a low pass filter. It does this because as it amplifies the tube is ‘fighting’ against the grid to anode capacitance. (Meaning as it is amplifying the grid to anode capacitance is charging and discharging similar to an astable oscillator.)

Millers capacitance = the grids capacitance times the anodes capacitance. This is what Millers capacitance is! (all interelemental capacitances mentioned need to include stray capacitance ;) )

Miller’s capacitance is normally associated with triodes but applies to all valves. It is ore noticeable in the triodes though (because pentodes and tetrodes have screengrids which ‘sheilds’ the valve.). Which is unlucky for all us audio designer builders (unless you use the low pass filter to your advantage ;) ) because as most of you know the preamp tubes are almost always dual triodes.


Right this is how it affects the audio circuits. I said in layman’s terms Millers capacitance affects low pass filtering. This is actually only ½ the story. Millers capacitance does have an effect on low pass filtering but it is not the be all and end all! Really its up to the input capacitance that decides it!

Input capacitance is measured by the sum of grid to cathode capacitance plus the grid to anode capacitance times thee stages gain + 1.

If you were to write this as a formula it would be:
InC=GK+GA*(A+1)

Where:
InC=Input capacitance
GK=Grid to cathode capacitance
GA=Grid to Anode capacitance
A=Gain of the stage

As the more knowledgeable of you should know. All these capacitances are really tiny, so they wouldn’t have much effect on the overall outcome right? Wrong! Because this is times by the gain of the stage it can have huge affects.

“Yeah so what if it makes a load of numbers change it’s the sound that matters” Most of you will be screaming at me after this brief theory lesson will say! It is true so lets take a few examples. Right lets take the good old 12AX7 OK? GK=1.6pf GA=1.7pf (I looked at tube data sheets for those I am not that much of a robot!!) lets use a gain of roughly 52 and a stray capacitance of 0.7pf on both GK and GA.
So:
InC=2.3+(52+1)*2.4=127.1pf of input capacitance.

A 12AY7 has a GK=1.3 and a GA=1.3 (keeping with the 0.7 stray and 52 gain) would equal:
InC=2+(52+1)*2=108pf
of input capacitace. As you can see the 12AY7 could be replaced instead of a 12AX7 for a quicker low filter cut off! (although there are other considerations to think about).

But do you know what? It isn’t that simple (what a surprise!) because input capacitance by itself does not affect low frequency filtering, as the more knowledgeable will know it is reactance which will decide frequency cut offs.

The formula for this is:

F=1/(2*pi*R*InC)
Where:
R=input resistance
InC=Input capacitance
F=Frequency

So lets keep a constant of 68k for the input resistance (standard value for an input resistor) So our 12AX7 example would equal:

F=1/(2*pi*127.1*68)=18.4kHz (1 dp)

Where as the 12AY7 example would be:
F=1/(2*pi*108*68)=21.7kHz (Again 1 dp)

This means that the 12AY7 example will cut off more of the low frequencies than the 12AX7 example. But as you can see there are many variables and chances to experiment! But also take into consideration (as microdmitry said) all valves are different!

This is my interpretation of the Miller effect micro please inform me if this is right or wrong! Also take into account I am 15 yrs old so don’t flame me for a few mistakes :lol:

Thank you, everyone for keeping this thread with intelligent points and arguments. I will (try) and inform you of all the different factors in choosing tubes!!!

:twisted:

Also anyone who has done any real research into the interelemental capacitances of different makes please state them. :p
 
#32 ·
Woah.... This thread has died, oh well lets cram it with more imformation :wink:

Cabinets so many choices?
Many tone heads claim that the cabinet you plug into is equal to about ½ of your amps overall tonalities. So I thought I would have my say in the matter!!!

Speakers:
This is an obvious one! Of course speakers will affect the tone (unless you are using 100% transparent monitors.) Many manufacturers include graphs showing the Tonalities of the speaker. These are basically as easy as reading a Graphic EQ so I won't go into it.

There are also many factors that contribute to the tone of speakers. Here is a brief rundown:
These are also referred to as Thiele/Small parameters.

FS:
This is also known as the air resonant frequency. A resonant frequency is the frequency at which the sound is loudest. This can give you a good indication of the speakers' character (the same rule applies to pickups!). If a higher frequency is the resonant frequency, the general tone will be brighter than one with a lower resonant frequency. Generally a speaker with higher impedance also has a higher FS although there are exceptions. This is also important to know if you can find the resonant frequency of the enclosure. If they resonate at the same frequency (IE the speaker vibrates at the same frequency as the cabinet) it will ring uncontrollably!

RE:
No it's not the lesson you had to sit through at school! It's actually the DC resistance of the speaker. This to my knowledge does not really represent much as far as amplification goes. This is because a signal is essentially an AC wave rather than a DC one. It is important to know that RE is almost always lower than Nominal impedance, which most speakers are measured. Some have the fear that the amp will overload but in fact it won't. Its hard to explain why, but its basically because as frequency increases the inductance also increases, meaning the amplifier will rarely see this load.

Qms, Qes a Qts:
Relates to the suspension when the driver reaches FS. These again have no real affect as far as tone is concerned. The Qts is equal to the sum of Qms x Qes / Qms + Qes. This Qts is also known as total Q,this represents th suspension affect of the transducer. Many recommend, that a Qts of 0.4 of below should be used in a vented enclosure and a Qts of 0.7 or above represents an open enclosure, could be used. This is just a guideline and you should really just follow your ears though!

VD:
In layman's terms the amount of air that a cone can push. Hence a speaker that seems louder will have a higher VD. As will a larger surface area speaker (generally speaking)

BL:
This is a bit strange. The test they use (I believe) is: a mass applied to the cone, then the amount of force the cone is "pushing" back is the BL number. Basically this is the "power" of a speaker, its not really "power" per se. It's more like the strength that the transducer is applying to the cone.

EBP:
This is also similar to Qts. EBP is the symbol used in many enclosure design formulas, in speakers it is used to determine whether the speaker is better suited to a closed of open enclosure. A rating of around 100 usually represent the speaker is suited towards an open-vented enclosure, where as a rating closer to 50 is normally suited to a closed back enclosure.

Sd:
Is the surface area of the speaker and is usually expressed in cm squared.

Xmax:
Represents the speakers impedance at resonant frequency (FS).

Those are the real Thiele parameters that really affect the usability of the speakers. But also there are also usable frequency ranges. This represents the point at which the frequencies are useful. Another way of thinking about it is: when you stand in front of a single speaker combo or cab, when you stand perfectly in front of it, its sounds weird but if you move to one side it goes. The "weird" sound is known as beamy or narrow. This affect is dependant of speaker size and frequency, as you want to try and avoid this don't pick a speaker that does this at a musical note, (say middle C). Here is a few examples.

Speaker size: Frequency:
6.5" 2,672Hz
8" 2,105Hz
10" 1,658Hz
12" 1,335Hz
15" 1,052Hz

There are many ways of measuring this affect. The numbers I have taken are the ones Eminence speakers use.

Next we have power handling. This should be either an obvious or complex subject depending on your musical preference and style. Firstly you need a speaker at least the rating of you amp, these ratings are normally conservative but still don't go under them. That is the simple part; the more complex part comes from the old rock 'n' roll "vintage" style of music. The earliest type of distortion used was speaker distortion. It occurs when the speaker simply can't get any louder and therefore distorts. This characteristic sound is normally associated with the old alnico Jensen's of yesteryear! It gives that trademark thick, rich overdrive with very low gain. The problem is choosing a rating. You don't want to run the risk of blowing a speaker so you have got to be careful. Of course with most modern playing styles this type of distortion is best avoided!

Magnet types:
As with pickups there are two main types of magnet used, either the old faithful Alnico or the Ceramic magnets. The short source of alnico means it costs a bomb to buy enough to make a heavy speaker hence the prices of some! As a general rule Alnico is generally warmer, sweeter with richer harmonics where as ceramics are usually classed as more muscular and aggressive sounding. Although this isn't always true and is just a basic generalisation, because no musical signal actually flows through a magnet so the magnet itself isn't invollved with tone shaping. Its actually the strength, weight and design around the magnet that affects tone.

Efficiency and sensitivity:
The sensitivity of a speaker is generally a rough indication of how loud it is going to be. If you take a 10w 100dB sensitivity speaker and compare it to a 100w 97dB speaker, you should find the 10W to be louder! But remember because it is louder it doesn't mean it will handle a higher power rating. (if you plug into a 30w amp it would most likely break!)

Speaker size:
As stated above about the useful frequency range, size matters! But not necessarily is bigger always better. 12s are normally used exclusively used these days but always remember there are other sizes. People believe that 10s are bright and 15s are boomy, but as a lot of other things regarding the music industry these are myths. They do have different frequency responses but still a 10" cone could be made to make as much/more bass than a 15".

The most dramatic affect that speaker size has on tone is the delay/response time (AKA attack). This is a very tiny time that is barely measurable but does actually affect the tone. If you take 10" cones they have smaller cones and therefore less space for the cone to travel to produce a sound. The results give a quicker more articulating notes, with a load of definition and character! Which normally accounts for the "jumpy" highs! On the other hand 15" cones produce a slower response time due to more space for the cone to travel in. Therefore they are slower producing a slightly less articulating attack. Which in turn can seem like the highs are less lively, making them seem bassier! As you would expect 12" cones are in the middle!! And is probably why many players favour them!! (Remember you can go higher or lower than 10s/15s but expect the effects of smaller or bigger cones to be amplified (pun intended!) )

Cabinets:
A cabinet is just a place to hold your speakers, and maybe rest a cold beverage on right? Wrong again their Jimmy. The amount of factors that affect an amps tonality and response are endless, way more than the factors that affect a guitars tone. The cabinet choice when paired with a speaker choice makes up roughly 50% of the amps tone, according to some experts.

Material:
This is an obvious one! Just like the wood of a guitar affects its tonality so does the cabinet wood. Just like any other instrument the way in which the wood resonates colours the tone. Although you also have to remember though that the strength of the wood plays apart, you don't want the cab to break when inside the back of a van do you! The industry standard material for making cabinets with is pine, which is usually plied to increase strength. I am sorry to disappoint anybody but I doubt that it is possible for the actual wood to make a difference (Eg. Pine Vs Ash or whatever. Most cabinets are covered it thick animal glue and tolex. This would hinder any chance of resonation, I believe that it's the stiffness, thickness, and construction (ply V solid) that would make any difference, if anything))

Generally speaking plywood or chipboard doesn't resonate as well as solid woods. Although resonation is not necessarily a good thing. Some claim a solid wood cabs make a "woolly" or unfocused. On the other hand some people love that vintage Bassman sound and think it's the dogs!

Open Vs. Closed:
This is a VERY long debate, which, in fact has wasted a lot of time when we should be practising! (Just like the Set neck Vs. Bolt on argument) Most people know the differences between the two and have already made judgements for those people feel free to ignore a lot of this part. This is mainly for people who don't know much about either or what exactly the sound like.

The best way to find out the difference IMO is to go down to your music store and try two identical (or very similar) models of cab through the same amp and note the differences. A Closed cab has a piece of wood bolted across the back of the cabinet so you are unable to see the speakers' magnet, whereas an open cabinet has nothing. (There are wide varieties that are ½ or ¾ closed which is like the fail-safe middle ground as far as cabs go.)

Open:
They sound more natural and transparent generally, with a wide almost surround sound feel. They also sound more "realistic" to some people's ears. There is also an emphasis on the highs although the bass response usually suffers due to the fact that there is partial phase cancellation due to the sound dispersing out of the back. I have to say though don't worry about recording issues due to the phase cancellation because it is only slightly present (hence the word partial.) Also because the speaker "drives" in a multi-directional manner it seems to be louder than an identical closed back cab.

Closed:
One of the main attractions of a closed back cab is the astounding low end, which is often fuller and tighter in tonality. Because the sound is only projected in one direction the mids are often said to be overly compressed or spongy. The high end response is said to suffer from this construction method as well all though I believe that the increased amount of low end makes there seem like less highs.

As with every part of gear choice neither is better just different. Nobody can make a choice for you its all up to you! I hope this has made the choice a little easier but we still have more points to cover!

Wiring:
Without taking into account the changes in impedances (which you should know already through the resistor parallel or series rules!) lets look at how the different wiring approaches affect tone. First lets look at safety. If you have two speakers in series, imagine one breaks what would happen? A broken OT most likely! Because you are running one into another if one of them breaks the circuit is broken, meaning no load is on the OT, which will destroy it. On the other hand if you wired them in parallel, the chance is reduced because when one blows the other keeps working. Keep in mind that the impedance will then change so still run to turn off the amp, but at least you will have more time to save your baby!
With that out of the way lets look at the tonal differences!

Series:
Generally speaking speakers that are wired in series sound looser and more "sloppy" which you may think is a bad thing but not always. This is also paired with less of a damping effect, which in turn makes it sound raw or unprocessed and open sound. So you can see it gives more of a Blues scream tone rather than smooth jazz although this is just a huge generalization.

Parallel:
Parallel wiring is another way to make a cab. Yet again it gives different results tonally. Generally the break-up on speakers end is smoother with a tighter bass response. It also has a large damping effect, which you can see as a good or bad thing.

There are other "hybrid" configurations that you can use, which give results that rest in between the other two styles!

Multiple Vs Single:
Here is another life-long argument about what is "the best" either many speakers or a single speaker. This is a VERY long debate and I don't want to cover it in too greater detail because almost everyone knows the difference between them. Obviously more drivers will push more air to the listener's ear, which in turn will make the amplified level seem to be larger.

The way in which it affects "tone" is a little complicated if you want it to be! I am not about to jump into a huge long theory about the human ear and how it works so here is a quick answer to how it affects tone. The more speakers there are in a cabinet the more there will be an effect similar to phase cancellation. This in turn increases bass response. Also as there are more speakers they react to the signal being passed through them at different rates, this is also true about the same make, model or any other similarities the speakers may have. This creates a sort of harmony and blending of sounds, which has become very desirable. As it can often be linked to almost any classic rock/metal band of the past! Some people also blend different models of speaker to create desired affects. There is no set way to do this and you never quite know what you will end up with but generally most people use on bassy speaker and one bright speaker together for good results, nothing is set in stone so experimentation is the key!

Baffle:
The baffle is the board that is in the front of the cabinet that holds the speakers, for those who didn't know. There are many variations and ways to do things which all produce different effects. I like to think of the baffle as like the neck joint on a guitar, because it connects the speaker to the cabinet so it can help/hinder resonation. Generally speaking older cabinets are made with thinner and looser baffles. These pass the vibration more strongly onto the cabinet which helps make it resonate more. This style of baffle is generally not used as much as it used to because it is considered to be unfocussed and "woolly". The tighter the baffle it clamped onto the cab the less the vibrations will be passed on, this will make more of the speakers tonal qualities to shine through. It also makes the cab have a tighter better-defined low end.

Cab sizes:
The size that a cabinet is made also affects the tone. I will not go into the great details of how and why all this happens I will just give the facts. As a rule of thumb a deeper larger cabinet would make a larger bass sound, where as a smaller cabinet would make a brighter sound.

http://www.webervst.com/spkrcalc/closed2.htm
Here's a link about working out the tone of different sized closed back cabinets!!

Enjoy! 8)
 
#33 ·
How does impedance effect the volume output of an amp + speaker combination? I have a SS head which is rated at 300 W at 2 ohms, 200 W at 4 ohms, and 120 W at 8 ohms. Will I get more volume through a 4 ohm speaker than through an 8 ohm speaker?

I'm sorry if this has been discussed before, but I couldn't find it by looking through the rest of this thread. Most people of whom I ask this question don't know, so it would be good information to have.

Thanks!
-Bennett
 
#34 ·
trajectory fish said:
How does impedance effect the volume output of an amp + speaker combination? I have a SS head which is rated at 300 W at 2 ohms, 200 W at 4 ohms, and 120 W at 8 ohms. Will I get more volume through a 4 ohm speaker than through an 8 ohm speaker?

I'm sorry if this has been discussed before, but I couldn't find it by looking through the rest of this thread. Most people of whom I ask this question don't know, so it would be good information to have.

Thanks!
-Bennett
As a rule of thumb if you mismatch impedances you lose a bit of power. :wink:

But it changes the overall tonality of the speakers themselves, going higher than the reccomend impedance (ie an 8 speaker into 16 ohms S.O) will tighten up the bottom end. It will also be more midd pronounced. Going lower increases bass and treble.

Becareful though some amps are more delicate than others! (if its a Marshall don't mismatch!!! they seem to be easily killed!) :p
 
#35 ·
hmmm... maybe I should re-work this question. I have the amp I mentioned in my previous post. Right now I'm powering a 4 ohm speaker cabinet. Would it be louder if I connected it to a 2 ohm cabinet? Would I get less volume through an 8 ohm cabinet?

In other words, is 100 W @ 4 ohms the same volume as 100 W @ 8 ohms?

Thank you. I'm very sorry I'm so confusable. :?
 
#36 ·
trajectory fish said:
hmmm... maybe I should re-work this question. I have the amp I mentioned in my previous post. Right now I'm powering a 4 ohm speaker cabinet. Would it be louder if I connected it to a 2 ohm cabinet? Would I get less volume through an 8 ohm cabinet?

In other words, is 100 W @ 4 ohms the same volume as 100 W @ 8 ohms?

Thank you. I'm very sorry I'm so confusable. :?
OK, looking at the back panel yes it seems like it would be louder with a smaller impedance.
:twisted:
 
#38 ·
Biasing:
Lets now move onto the controversial subject of biasing. Why do we need tubes to be biased? Well, as most of you should know tubes/valves aren't JUST for amplification use. When they were invented they were used for almost everything, including: Oscillators, non-audio amplifiers, TVs, Switches (And the list goes on!) When thinking about tubes think of them as another component. You need to "set up" the tube to get it to do what you want. Basically this is biasing! The bias point "selects" a number of things. These include: Class (A/AB/B etc); Gain; Output; Efficiency (amount of useful output compared to the input); Headroom; Distortion (what type of distortion I.e. cross-over/symmetric etc.) (the list goes on!) Basically bias is a "middle ground" of all these factors, and it CAN be changed from factory specs! But you need to know what to do if you want the amplifier to perform correctly. So how do we do this? Every triode (or anymore active element valve) needs to be biased, contrary to common belief this includes the pre-amp! Biasing a pre-amp is pre-determined and is not "adjustable" when changing tubes. You can change the bias by swapping out the anode and cathode resistors. You need to work out what the grid voltage is when the plate current is 0ma; you then get a halfway point between the grid voltage and saturation (it will be a negative number.) The pre-amp bias is usually determined from an idle point (0v at the grid), You can't apply a negative voltage to a grid with normal measures so we ignore this factor and change the cathode resistor instead! You then have to work out the voltage applied to the anode resistor. Then you use ohms law to work out the current at the anode. A minute amount of this current goes through the grid onto ground, but when biasing we ignore that and presume all the current goes through to cathode to ground! So you take the current at the anode (using ohms law again) to find out the voltage. Now you have to take the grid voltage (which is 0v) and take away the cathode voltage. This should be the same voltage as the ½ waypoint (if it is biased!)

Now lets get onto Power-amps. These are many ways to bias a power amp, the most common are fixed and cathode bias. Fixed bias really has two meaning now, it used to be a method that used a trim pot (that adjusted the negative bias that passes into the grid) this requires another tap on the output transformer though! Fixed bias is also a word now associated with the "mesa" biasing type, this is non-adjustable (well not easily adjustable it requires calculation and resistor changes!) and it is basically the same as the first type in terms of taps and voltages. There is also a type called Cathode bias, has no bias supply. Meaning no extra tap on a transformer is needed. It requires only one resistor! Which acts like the cathode resistor I explained in the preamp tubes section! Some people put a resistor in parallel with a potentiometer (pot) to allow greater flexibility. Some people think that a cathode bias "makes" an amp Class A. It does not! The misconception must have come along from single ended amps. These HAVE to be class A! Most designers also add a cathode bias to these amps because cathode bias yields less output (SE amps are generally used for low watt applications.)

There are many ways to bias power-amps some of these include using resistive loads, oscilloscopes and wave generators. I believe ways that do it like this are far from perfect! First of all you connect a resistive load, which doesn't vary with frequency like speakers do. Then you send a sine wave (about 1k) through the amp set the volume high until the sine wave starts to flatten. You then adjust bias until it gets round, crank volume again. And so on. Again, to me that's not accurate because: 1.) Your tools need to be calibrated to perform such tasks accurately, and 2.)Can you trust your eyes? Have you heard of optical illusions? How can you tell the point where they are starting to get round? See, to me that's not too smart! Although it has some uses if you have an amp with no markings or you don't know the bias point, but wouldn't that be more suited to a tech?

Anyway that's the classic way to do things, another way of biasing the power-amp is to measure the plate current. This is not as simple as getting a multi-meter and attaching it to a tube though! You need to measure the resistance at the primary side of the output transformer (while the amp is off! The primary is the side with the tubes on!) Then write them down, turn on the amp and measure the voltage drop between the both sides of the transformer (subtract the smaller from the bigger. You might want to attach the probes into position first to stop the chance to you slipping and getting electrocuted!) You then take the voltage drop and divide it by the resistance (In a formula it would look like V/R where V is voltage drop and R is primary resistance.) You now have the anode or plate current, if more than one tube is used divide this by the number of tubes to get the current per tube, voila now (if you have got a schematic or documents that came with your amp handy) you can bias your amp. Remember the bias points are just "ballparks" you can go either side of them (just not too much!) for hotter/cooler tubes.

What your amp didn't come with documentation? No schematic has the bias values? Never fear! It can still be done! This is a bit tricky but once you have worked it out you never need to pay a tech to do it again! So this is how you work out plate current values. First you need to work out what voltage your power transformer is, this could be marked on it (or at least a number and make so you can look it up!) if not the schematic should have it on their (it's usually in the form X-0-X for centre tapped transformers. X being voltage. E.g. 300-0-300 would be 300v.) You also need the value for plate dissipation (tube data sheets should have these. Look under the heading "maximum ratings" and look next to Plate Dissipation.) For class AB amps (the majority of guitar amps) you need to use a percentage of dissipation of 70% (maximum) for Class A use a percentage of 100% (A rule of thumb is that if the amp has a voltage of more than about 250v it is AB, if it is on the borderline get on the phone to the manufacturer. If it is Single Ended it has to be Class A.) Now you have got that information you can work out the plate current. Using the Formula:

P*(D/V)

When:
P = Percentage
D = Dissipation
V = Voltage

To take a few examples I will use a few famous amps! Firstly the Marshall (2204):
0.7*(25/325)= 0.054 (2 dp) This is in amps so in Ma this is 54Ma! This is the maximum some players go down to 50/60% this is using EL34 tubes! (Per tube!)

Now a Fender Vibro champ:
1*(12/315)= 0.038 or 38Ma per tube (I know you don't need the 1 but its just to show that its single ended! So it's Class A!)

Now a Hiwatt DR 201:
0.7*(25/350)=0.05 or 50Ma.

I think you get the idea now here are the dissipation ratings for the most common output tubes:
EL34=25Watts
6V6=12Watts
EL84=12Watts
6L6=22Watts
6550=44Watts

(Note this approach doesn't work for Cathode Biased Amps! But most of the latest amps don't come with cathode biases anyway! As stated earlier mostly it's for single ended amps like the one I am making!)

Now you know what you are aiming for you can start biasing! Firstly you need to MEASURE the current at the plate. This is rather hard to do so there are a number of ways to do it. I would use a resistor of 1 ohm (high wattage 3 or more with a 1% or better tolerance) and attach it to the tubes the output section (Cathode.) Now if you work out the voltage drop across the resistor (sing a Multi meter) you get the cathode current. You assume all the current from the cathode goes to the anode (or plate) so you get the plate current, if you want to be totally accurate you measure the current at the screen grid as well, this is usually small so it can be ignored (plus without adding it your tubes run a little cooler so they will last longer!) If you are using a 9-pin power tube (like the EL84) the pin number to connect to is 3, for any 8 pin power tube you will wan to connect to pin 8 (as shown in the picture below!)


That is the basis of biasing an amp I am not claiming that this is the "best way" or the "correct" way but is the way that I do it.
:twisted:
 
#39 ·
Regarding speaker ratings... is transient response a useful thing to know when shopping for guitar speakers? I realize the importance with subwoofers, but I really don't understand the concept enough(although I have a good handle) to know if it would be meaningful information for a speaker that generally hangs around higher frequencies.

I'm kind of curious in case I end up buying/building a new cabinet I will be doing a 2x12 and I want to make sure I get the most out of it that I can. Not just "half of a 412" so to speak... I haven't paid attention to guitar loudspeaker technology in a while. I know personal audio has come a LONG way in the last few years with speaker efficiency.

Any insight?
 
#40 ·
jay ratkowski said:
Regarding speaker ratings... is transient response a useful thing to know when shopping for guitar speakers? I realize the importance with subwoofers, but I really don't understand the concept enough(although I have a good handle) to know if it would be meaningful information for a speaker that generally hangs around higher frequencies.

I'm kind of curious in case I end up buying/building a new cabinet I will be doing a 2x12 and I want to make sure I get the most out of it that I can. Not just "half of a 412" so to speak... I haven't paid attention to guitar loudspeaker technology in a while. I know personal audio has come a LONG way in the last few years with speaker efficiency.

Any insight?
oops I have missed this every time I have rowsed this forum! :oops:

Transient responce can be important as a player wants it to be. Most of the time though we just ignore it and go for our old favourite speakers in a cabinet. Propably some of the best as far as transients are concerned are probably the Celestion "Neo" magnet speakers. Although to a lot of peoples ears they seem really bright and fizzy in the top end. If you want a responsive speaker it is probably best to get one with a low QTS value and don't overate the speakers too much (if a low power amp is driving a high power speaker it becomes less responsive to changes in amplitude and transients)

:twisted:
 
#41 ·
power freak said:
jay ratkowski said:
Regarding speaker ratings... is transient response a useful thing to know when shopping for guitar speakers? I realize the importance with subwoofers, but I really don't understand the concept enough(although I have a good handle) to know if it would be meaningful information for a speaker that generally hangs around higher frequencies.

I'm kind of curious in case I end up buying/building a new cabinet I will be doing a 2x12 and I want to make sure I get the most out of it that I can. Not just "half of a 412" so to speak... I haven't paid attention to guitar loudspeaker technology in a while. I know personal audio has come a LONG way in the last few years with speaker efficiency.

Any insight?
oops I have missed this every time I have rowsed this forum! :oops:

Transient responce can be important as a player wants it to be. Most of the time though we just ignore it and go for our old favourite speakers in a cabinet. Propably some of the best as far as transients are concerned are probably the Celestion "Neo" magnet speakers. Although to a lot of peoples ears they seem really bright and fizzy in the top end. If you want a responsive speaker it is probably best to get one with a low QTS value and don't overate the speakers too much (if a low power amp is driving a high power speaker it becomes less responsive to changes in amplitude and transients)

:twisted:
Yippy! I might have to check those Neo mags out. I mainly play jangly clean stuff, so that extra bright top end might be worth it for the super tight response. It actually might fit in perfectly. In fact, I might order one of the G12 Century Vintage series speakers in the next week or two and pop them in my 1x12 cheapy practice amp to see what happens. $200 to have a brand new, usable amp is sounding good.
 
#42 ·
Right tubes? right amp? HELP P Freak!

Hi Power Freak, you seem to be the right guy to ask about Tubes and the like! I'll level with right now... I know nothing about them except that JJ's are commonly used to replace stock tubes in amps.

OK, have you ever heard of... PM 606s ( power amp) and Ecc82 (per amp)? I'm on the verg of buying an ex demo Peavey 5150 combo that has been revalved with the said tubes and I can't find any info on them!! :(

cheers, Steve :)
 
#43 ·
Re: Right tubes? right amp? HELP P Freak!

Shredmonster said:
Hi Power Freak, you seem to be the right guy to ask about Tubes and the like! I'll level with right now... I know nothing about them except that JJ's are commonly used to replace stock tubes in amps.

OK, have you ever heard of... PM 606s ( power amp) and Ecc82 (per amp)? I'm on the verg of buying an ex demo Peavey 5150 combo that has been revalved with the said tubes and I can't find any info on them!! :(

cheers, Steve :)
ECC82s are quite common, they are also known as 12AU7. They have a much lower gain than the ECC83s, just over a 10th of the gain in fact! This would completely change the feeling of a 5150; instead of being a huge gain monster it would feel less powerful and more "controllable" which is good thing IMO because I hate too much gain! They do however have a huge output (ECC83=3ma Ecc82=10ma) so it would push the power amp harder and turn it into a more "Plexi" like sound and feel. It should also give a wider range of volume and gain, while using the knobs.

I am sorry to say I have never heard of a PM606, Maybe where you are getting it from got confused with a 6L6/KT66?
 
#44 ·
Tubes n stuff

Excellent info PF. I had to ask about the 606 but I fig the guys at the store got it wrong too and ment 6L6 which I've gathered in my tube ventures as being rather good.

The Ecc82's producing less gain shouldn't be a prob as I too play with less gain these days and the 5150 has tons of that.

:D

Thanks again, great stuff!!

Steve.
 
#45 · (Edited)
About a year late....

power freak said:
6550: Is a tube that Marshall started sing in Marshall Majors, and is a firm favourite with Ritchie Blackmore. But originally it was used as a high grade audio valve. KT88s have a signature bass which is heavy yet tight, and also screaming highs.They are one of the most high output valves on the market. It distorts very slowly (hard to distort) and have that 'hard' valve sound compared to an EL34s soft sound. There are also KT90 and KT99 versions which are even higher output. 6550s are normally associated with heavy metal but especially 'shredders' due to their imense clarity.
KT88s and 6550s are NOT the same thing, although they are fairly close. One major difference is KT88s are much better made generally and can handle much higher voltages. They are also a bit warmer.

Marshall Majors and 6550s is a bad idea. I can tell you all about it being a Major owner. It will eat any new 6550s as well as most NOS ones except GEs as soon as you turn it on, they can't handle the plate voltage of 650-700 watts. KT88s fair better, but the only KT88s made today that can really handle the voltage from a Major is the SED, and barely. Given that the original Genelex tubes often sell for as much as $650 per tube (I am not kidding either), the only logical option left is the SED.

Richie Blackmore used GEC KT88s. With all the input boosters he used with his Major, he went through a pair of tubes in three or four days and fried many tube sockets and transformers as well.

But you do seem to know a lot about tubes.. what would you put in a Marshall JCM 900 SL-X 2100 for preamp tubes? I am leaning towards JJs although a lot of people really like the Sovtek 12AX7LPS in Marshalls these days from what I have heard. And I am going to drop in some SED 12AX7s into my Major - they are exactly as I hear well made - no thin wires inside that I can barely see and they weigh about twice as much as your regular new 12AX7s... I can tell they are defintely well made but I hear they have too much clarity especially in the high end. But I think I am going to like that in an old Marshall!
 
#46 ·
Thank you "powerfreak" for the very good infos !!!!!!!!! ive printed 'em all !

Ill share my experience with tubes to date, maybe someone could use it.

First my equipment: 2x Marshall SLP reissues ( with mercury magnetics trannnies and chokes) , 4x 1960 AB cabs loaded with Celestion 80 watt neo's , 1x Eventide H8000A in the fx loops.

My conclusions.....

MHG set from GT ? not good
GTecc83s from Gt? not good,terrible.
GT SAG mpi phase inverters ? not good.go quickly (panic, thin sound).
GT12ax7m ? very good.GT12ax7m ? very good.GT12ax7 r3 ? very good
GT 12ax7r2 ? havent tried 'em yet

Gt6CA7ge's very good,damn good !!!! But...2 sets blew and were replaced by GT (here in europe our warranty lasts longer than in the states,be careful,and watch out for those mikes ! Preamp ? gimme that tubetech !)
[ I spoke to the head tech at Groove Tubes in the US, he says the GT-6CA7GE likes to run on a bias current of 40ma with a bias voltage of between -40vdc and -42vdc ]

I am currently fixin to try the GT 6550 R in one of my plexi reissues, for a side by side compare to the GT6ca7's, perhaps ill get back later.....
[ MARSHALL EL34 to 6550
1.) Change the bias resistor to 47K (located above the bias pot).
2.) Set the bias pot to max (around -38 volts)
3.) Locate the purple feedback wire (that is connected to the 8-ohm speaker tap) and solder it onto the 4-ohm speaker tap.
4.) Install the 6550's and re-bias the amp. ]

Marshall sent me chineese peamp tubes as replace, TERRIBLE. They sent svetlana golds as power replacements, okay, dont compare to GT6ca7.
Stock power tubes chineese ruby EL34Bstr, terrible.Stock preamp tubes, terrible.

P.S. those celestion centuries (80 watts) are very good !!
 
#49 ·
Just a point on the psycho acoustics thing...

I reckon one reason that amps sound different at different times is your position relative to the amp...sound loses energy very quickly, and where you are will affect the way you hear the sound, as well as the way the room is arranged as this affects absorbance/reflection/refraction and diffraction. There's more than just electronics to take into account, acoustic physics is important.

Psychological factors do affect it a bit though, if you're in a creative mood you will likely be concentrating more I suppose so it could sound 'different' in a way. You can't say that it's all psychological though as I have heard that some people can tell teh difference between different types of violins and other instruments just by listening to them AND GET IT RIGHT, they would surely have to be psychic to do that if it was all psychological.
 
#50 ·
NNS said:
Just a point on the psycho acoustics thing...

I reckon one reason that amps sound different at different times is your position relative to the amp...sound loses energy very quickly, and where you are will affect the way you hear the sound, as well as the way the room is arranged as this affects absorbance/reflection/refraction and diffraction. There's more than just electronics to take into account, acoustic physics is important.

Psychological factors do affect it a bit though, if you're in a creative mood you will likely be concentrating more I suppose so it could sound 'different' in a way. You can't say that it's all psychological though as I have heard that some people can tell teh difference between different types of violins and other instruments just by listening to them AND GET IT RIGHT, they would surely have to be psychic to do that if it was all psychological.
yea, weve all had those gigs where nothing sounds right and you try to "force" it !!!

there is some serious technical knowledge available in this thread and while I may understand some of it, I cant help thinking about its true "value" when it comes to buying a new amp or getting it re-valved at your local shop....

Im looking at it like this...
you buy an amp - mess about with it and get the sound you want.....
when it starts sounding crap you take it to a shop..
they fix it up with new valves.....
it sounds good again...

TBH im only playing devils advocate here as I do all my own maintenance..
so what am I getting at?

well, I think you can "worry" over your equipment only so much.... when there is much to worry about on your actual instrument...

anyway, im gonna buy a carvin V3 soon, im sure that one of you very clever valve guys (at 15 !!!!! damn im stoopid!) could tell me why this would be a bad idea but.... im gonna get it anyway and im not gonna worry about it....

but its nice to know that you people are out there !!! especially when I need to revalve my V3 ;)

awesome knowledge......
 
#51 · (Edited)
Hello everyone. I am a new member here an thought I would add some additional information regarding tubes on this thread. Power Freak has helped everyone out regarding tubes and what may work in your amp and so on. I thought I would share some information about how you know when a tube is bad and may need to be replaced.

Replace the tubes when:

* It is broken, and/or there is a white spot on the top or sides of the tube.

* The "getter" coating found in these areas is normally black or silver colored.

* It tests weak or shorted. Always replace a shorted tube, even if it tests good. Shorts can damage expensive amplifier parts. You cannot afford to lose your amplifier during a performance. Professional players minimize downtime by replacing the power tubes every few concerts. The price of tubes is cheap compared to the embarrassment of losing an amplifier on stage! The amplifier starts to sound bad, especially when first turned on.

So how do you know when tubes are starting to fail? Consider the following: Small-signal (preamp) tubes (12AX7, 12AU7, 12AT7.): You may hear a crackle for a short time after the amplifier is turned on. Then it quiets down. Or the amplifier may "howl" at high volumes, or buzz on certain notes all the time. These problems get worse, and eventually you will be replacing one or more tubes.

Power tubes (6L6, 6V6, EL-34, 6550, etc.): Upon turning on the amplifier, the sound may be hazy, with flabby bass and scratchy treble. After about five minutes of this, the sound starts to clear up, and the amplifier sounds fine from then on. As the tubes get weaker, it will take longer for the sound to clear up. Eventually you have to replace the power tubes as a set. For reliability we strongly encourage you to replace all power tubes at a time, even if one or more tubes are still good. Rectifier tubes (5Y3, 5U4, etc.) are not in the signal path and do not affect the sound as much. However, if you notice more distortion than normal when playing at high volumes, the tube is probably half-dead and should be replaced. Tube Matching Please note that we are talking about matching power tubes such as 6L6, 6V6 and EL-34. I can tell you from long, hard experience that matching power tubes affects the sound of your amplifier. Compared to random tubes, an amplifier with matched tubes will provide slightly more power and a reduced hum level. In most cases, the improvement in sound quality will be slight, but worthwhile.

Rectifier tubes (5Y3, 5U4, etc.) are not in the signal path and do not affect the sound as much. However, if you notice more distortion than normal when playing at high volumes, the tube is probably half-dead and should be replaced.

Thanks.

PortCityMusic
 
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