A guide to choosing tubes and cabinets! - Page 2 - Jemsite
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post #16 of 84 (permalink) Old 03-02-2004, 12:48 PM Thread Starter
 
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Quote:
Originally Posted by Al M
You dont have to get a trim pot installed though!? The guy at euro tubes told me he can just supply tubes for mesa amps as long as you tell him its for a mesa they will work fine.
Not all vendors are willing to do that

Also its not only the current boundaries of a tube that matter! Mesa's screening process allows them to see if tubes will develop a problem later in life I reccomend a bias trimmer on any amp that doesn't have one. It allows a wider range of tubes and sometimes Mesa's stock bias resistor goes off value (all components do at one stage or another) this will make the sound gradually out of bias you probably won't notice until you find a stock one. THis is the logest I have ever talked about Mesa/Boogies *shudders*

Grindfiend it is possible to adjust mesas with a quick mod. 'Better' is debateable but I would like the added reassurance that I could use any tubes.

To clarify the Mesas don't self bias!! some people allthough not on this board (luckily) seem to think that mesas automatically adjust to any tube. Back to the point normally the mod is a quick replacement of a resistor (I think some use parralel resistors too) for a trimmer.

Mr Orange Mesas (or any amp for that matter) can take pretty much any preamp tube without modification. The bias for pre-amp tubes (yes they are biased!) is pretty variable. I think it is because the original specification for pre-amp tubes is still pretty close to what they are made like now where as power tubes have drifted. I haven't done any research on this but some of the modern measurings seem way off for power tubes!

judasbane I will look into that when I have more time but there area few swaps that can be made. A KT88 will be a straight swap for a KT90 it is just a 'newer' or military version of the tube. With a quick glance at a data sheet it seems like it may be a straight swap between a KT88-KT66. DON'T try it though I have done no research yet. Also the maximum voltage for the 2 valves is different a KT88 can work in higher voltages. Also if people didn't know the KT88 and 6550 names are used interchangably.

sanchez There are many ways to bias an amp. You will need to know the bias voltage to do it no matter what! (Even though its actually the current that needs to be 'biased' its harder to measure.) I think the easiest way is with a VOM meter or similar. I will post up an in depth 'guide' when I have a bit more free time.
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post #17 of 84 (permalink) Old 03-02-2004, 04:13 PM Thread Starter
 
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i just looked up some info on KT88 (6550) and KT66 (6L6) tubes. They both have the same negative bias, which means they can be changed without modification (according to a few internet sources) they also use an octal base. Although some amps may need to be 'compensated' for the change in output and tone.

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.

6L6: This started out in the guitar amp world in fenders designs such as the Bassman and Tweed. It has a sweet and warm tone with alot of balance. As fenders got 'hot rodded' the valve has taken on a new side. It now appears in many high gain amps. It's distortion is less scooped than an EL34 and less bright than a 6550. Its output is much lower than a 6550 and an EL34 and breaks into distortion evenly. THis is probably the most 'alround' valve because it appeals to not only rock and blues players but jazz players, heavy metal players (and the list goes on).

EL34: I just though I'd do a quick analysis of EL34s in general, I must point out though that a change of bias is required to swap these! They are scooped in tonality and are favoured in Marshalls. THe output is in-between the 6550 and 6L6. They have a character 'soft' sound with a squishy treble. They break up pretty quickly and alot easier than 6550s and possibly quicker than 6L6s (although there is alot of argument). The 'Mullard' sound pretty much characterises the EL34 sound

Thats just a quick analysis, I will look at models and brands at the weekend or some other time.

This thread has just become stickied!!! Lets try and keep it full of information, tips and reviews. Anyone feel free to review a tube you have just bought and liked/dis-liked/broke
:P
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post #18 of 84 (permalink) Old 03-03-2004, 03:17 AM
 
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Quote:
Originally Posted by power freak

Mr Orange Mesas (or any amp for that matter) can take pretty much any preamp tube without modification.
Yup. I knew that already. My example was just to point out that if you want your Mesa to sound like with the old "mesa" tubes, you just might have the best luck with Sovteks.

As for the biasing projects, check out the Bias Master. I've seen one in action, and it makes biasing VERY quick and easy. All you need is the gizmo and a screwdriver!

If I remember correctly, 6550s were used in Marshall amps that were imported from UK to US. The EL34s couldn't take the overseas travelling, and were replaced with 6550s in the US. The EL34 is of British design and was not at the time widely available in the States; or something like that.
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post #19 of 84 (permalink) Old 03-03-2004, 04:16 AM
 
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"One tube sounds better than another" statements are BOGUS. First of all one needs to define "better". There are several criteria that make a tube objectively "better":
1. Build quality (mostly affects microphonics)
2. Filament shielding/hum cancellation
3. Vacuum strength - affects tube life

Any decently built tube (say a Sovtek or JJ or Svetlana) does well on all three thus making it nearly impossible to tell which one is better.

There are a couple factors that make tubes different (not better or worse):
1. Gain
2. Transfer curve shape (which in part defines gain, too)
3. Capacitances between electrodes (in real life circuits this is affected by gain, too - see the definition of Miller effect).

These three will affect the tone, but there's NO WAY to tell if any given tube is better or worse unless you try it IN YOUR particular amp. For example tubes with higher interelectrode capacitances may do better in some stages of high gain amps, because these capacitances are used (along with Miller effect and high resistance on anode) to tone down the "sizzle". Yet they can make your amp sound worse if used in other amplification stages. Same thing with gain. Higher gain tubes can be detrimental or beneficial to the tone of your amp depending on the amp (and channel, and stage) in which the tube is used.

Guitar player must also NOT expect any dramatic change from changing from one tube to another. If you're swapping a non-faulty tube for another brand the change in tone will most likely be purely psychological. Your ear fatigue affects your perception of guitar tone a lot more than even $80 NOS Telefunken tube.

Do not rely on rhetoric of tube sellers, remember, they're SELLERS, their only goal is to get you to buy more tubes to "try them out".

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post #20 of 84 (permalink) Old 03-03-2004, 07:36 AM
 
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the tech i took my amp to actually let me try different tubes in my preamp stage! As in sit there and replace them, try, have a play, replace, etc, repeat....

wil..
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post #21 of 84 (permalink) Old 03-03-2004, 01:05 PM Thread Starter
 
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Quote:
Originally Posted by microdmitry
"One tube sounds better than another" statements are BOGUS. First of all one needs to define "better". There are several criteria that make a tube objectively "better":
If I didn't make it clear in some cases I meant some people find Brand A better that Brand B because............. (statemenst about filament noise, frequwncy response, output and gain here!)

I have just looked at a few sites. I will try and finfd the scope readings for some tubes and explain them!!
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post #22 of 84 (permalink) Old 03-04-2004, 01:55 AM
 
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See, that's what I'm saying. Those people should always refer to a particular amp and particular place in that amp where they claim it "sounds better". And even then you shouldn't expect anything but barely noticeable difference.
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post #23 of 84 (permalink) Old 03-04-2004, 01:58 AM
 
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posted reply twice. deleted.
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post #24 of 84 (permalink) Old 03-04-2004, 03:24 AM
 
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Quote:
Originally Posted by microdmitry
Guitar player must also NOT expect any dramatic change from changing from one tube to another. If you're swapping a non-faulty tube for another brand the change in tone will most likely be purely psychological. Your ear fatigue affects your perception of guitar tone a lot more than even $80 NOS Telefunken tube.

Do not rely on rhetoric of tube sellers, remember, they're SELLERS, their only goal is to get you to buy more tubes to "try them out".

Well, I thought preamp tubes didn't make that much difference until I had a chance to do some swapping between chinese, Sovtek EHX and JJ 12AX7s in my own amp. I noticed differences when it came to character, noise and gain. It didn't make the amp become something totally different, it just seemed that different brands emphasized different aspects of the sound. I was quite suprised that the changes were so obvious, I wouldn't give credit of them to ear fatigue, paranoia or some weird psycho-acoustical phenomenon.

But it's true that you cannot save a lousy sounding amp by buying expensive tubes. If it's good, it'll sound good.
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post #25 of 84 (permalink) Old 03-04-2004, 04:13 AM
 
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And the thing is, there's no way to tell that, say, Sovtek will be better for all amps for all players. There's even no way to tell if you will like the tube you like today tomorrow. Have you ever had this experience when you totally love your amp one day and hate it the next day? You play the same guitar, through the same cabinet using the same settings and the same cable, yet one day your amp sounds smooth and the other it seems that somebody is sanding your brain with coarse sandpaper. I've even measured the voltage in these two situations - the voltage was the same both in the outlet and on the tubes.

The only difference is that one day I was relaxed and the other day I was tired.
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post #26 of 84 (permalink) Old 03-08-2004, 07:46 AM
 
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Yes! Indeed!

And the problem of induction! If all A are B, and C is A, then C is B; but how do we know that C is B tomorrow? What if the current paradigm changes while we're asleep?

My intention isn't to get personal by any means, but all these arguments are getting to a territory where we're sort of walking the fine line between relativism and nonsense, to use a vai-ish expression.

I don't deny the existence of psychoacoustics but hey, come on... That fact that our mindset(or mood or headspace or whatever term you wish to use) affects every damn thing we do will not survive as an argument for making everything subjective and relative. You might love your wife today, but hey, you might hate her tomorrow so go ahead and screw your neighbour's wife. You might be better off with her... Or maybe she'd just be different, not better or worse. But in a way, it is very subjective. There are millions of valid guitar tones.

I'd say, try out stuff. Stick with what you like. See what floats your boat. Goes for preamp and power amp tubes, dogs, gorillas, amps, guitars, chicks and _________________(fill in the blanks, folks). Unless you are a very religious person and believe that God will eventually direct you to the things that are the best for you.
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post #27 of 84 (permalink) Old 03-08-2004, 10:33 AM
 
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Quote:
Originally Posted by Mr Orange
Goes for preamp and power amp tubes, dogs, gorillas, amps, guitars, chicks and _________________(fill in the blanks, folks).
Now, how can I get these markings off my screen...
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post #28 of 84 (permalink) Old 03-09-2004, 01:50 AM
 
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Quote:
Originally Posted by Mr Orange
I'd say, try out stuff.
You'll probably go broke if you "try out" as much stuff as I did. 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 ) 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,
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post #29 of 84 (permalink) Old 03-09-2004, 03:23 AM
 
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Quote:
Originally Posted by microdmitry
You'll probably go broke if you "try out" as much stuff as I did.
I'm pretty sure about that as well. I'm struggling, day by day...

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

Quote:
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.

Quote:
Even the most discriminating guitar player (even Eric Johnson ) 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...

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.

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

Quote:
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...
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post #30 of 84 (permalink) Old 03-10-2004, 04:41 PM Thread Starter
 
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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*6=18.4kHz (1 dp)

Where as the 12AY7 example would be:
F=1/(2*pi*108*6=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

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!!!



Also anyone who has done any real research into the interelemental capacitances of different makes please state them. :P
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