Knowledge on tube amps

[cobb]

Hey guys. I just wanna gather some knowledge about tubes amps. Hope some of you guys can enlighten me.

What are the different types of tubes used on tube amps (power tubes?). How does different tubes used on a tube amp differ in terms of tone? And how do you select the type of tube for specific tube amps?

 

[CyanideJunkie]

Wah, where to start...

Well for power tubes there are:

-EL84
-EL34
-6L6
-6V6
-KT88
-KT66

And for preamp tubes there are:

-12AX7 (highest gain factor of 100)
-5751
-12AT7
-12AY7
-12AV7
-12AU7 (lowest gain factor of 19)

The biggest changes in your tone would depend on your amp's circuit and the speakers. Tubes lend a subtler influence, although it can be said that good tubes can make an amp audibly sound better.

For tube amps, most manufacturers will list out the tube complement along with a layout of the tube positions and their roles. Others might require a bit of research.

 

[Vax]

Haha looks like you did start another thread. It's a pretty big topic in and of itself, so we'll just cover the bare basics. There are two broad categories of tubes in an amp: preamp and power amp tubes. The preamp takes your initial signal from the guitar, makes it hotter, then passes it through the EQ section of your amp. This processed signal is then put through the power amp, where the power amp tubes are, and is further amplified before sent to the speaker.

What we generally hear from low-volume, low-wattage tube amps breaking up is preamp distortion. Some examples of (but not limited to) preamp tubes are the 12AX7 and 12AU7. This sounds good, but when you allow the power amp section to distort by cranking the amp's volume really loud, that's when the amp sounds great. If you want to hear power amp distortion, stand really far away. The EL84 is an excellent power amp tube specimen.

Tube choice is a matter of personal preference, but perhaps uniquely in Singapore with HDB housing and neighbors ready to complain, it's more a practical matter--very few of us are afforded the luxury of being able to hear the various types of preamp/power amp distortion with different tubes. We could go on to discuss the variances in tube tone, but I doubt it will be of much benefit since most of us can't crank our amps past 9 o'clock

 

[Godspeed64]

What's often overlooked at is the circuit of tube amps itself. Most people think an EL-84 amp will sound like an EL-84 amp (eg. Common misconception that it will sound Voxy).

Like how some people shun the Vox Tony Bruno series for having 6V6 or for the Night Train 50 for using EL34s; they believe that they do not sound like Voxes (which they REALLY do). Not saying that the tubes don't make a difference, but never overlook the design of the amp is based on.

Oh and Cyanide missed out one of my favourite tubes, the EF86!

 

[cobb]

Nice. Thanks for the input guys! Like what Cyanide said, there are various combis of tubes can be used. I've read online where people use the same tube model but different brands. (e.g JJ tubes, EHX,...) So how does different brands of tubes matter? What is more recommended?

I've got a blues jr. However, theres someting weird going on. Pls enlighten me on how to solve this issue:
Everything plays on fine but whenever i hit a C# note on the guitar, the amp produces some weird hissing noises! Any other note is fine but just the C#. Is there any way to solve this issue? Are the tubes dying out?

 

[Godspeed64]

Resonance issue. I suppose on that amp the C# of that pitch is the natural frequency of a part that is causing it to oscillate whenever that particular note is struck.

I got the same problem with the room. Doesn't like them Gs haha

 

[CyanideJunkie]

Oh and Cyanide missed out one of my favourite tubes, the EF86!

Aiyo cover basics only mah! I'm also a fan of the EF86 preamp circuit! Too bad Vox discontinued their Heritage series...

Nice. Thanks for the input guys! Like what Cyanide said, there are various combis of tubes can be used. I've read online where people use the same tube model but different brands. (e.g JJ tubes, EHX,...) So how does different brands of tubes matter? What is more recommended?

I've got a blues jr. However, theres someting weird going on. Pls enlighten me on how to solve this issue:
Everything plays on fine but whenever i hit a C# note on the guitar, the amp produces some weird hissing noises! Any other note is fine but just the C#. Is there any way to solve this issue? Are the tubes dying out?

Different tube brands = different flavours (best way I can describe it)

Let's just take your JJ and EHX 12AX7s for example. JJs are known to be on the darker side EQ-wise, so personally I would use them to tame the high end of a let's say, JCM 800. EHXs are quite bright, so one could use them to add some sparkle into a rather muddy amp. Where you place your tubes also matters. Consider whether your amp is a single or dual-channel model; know which tube positions are in charge of what.

For instance (deep breath):

My Jet City 20-watt has 5 preamp tubes(V1 - V5). This is a single-channel Marshall-style amp, so it has the capacity to be a bit dark-sounding. V1 handles the 1st gain stage(clean to mild crunch). I like my cleans to sparkle, so I put a Tung-Sol 12AX7(bright in my experience) in there. After that the signal goes into V2 which handles the 2nd and 3rd gain stage. Being that I like my overdriven tone to have a solid low-end and to avoid having overbearing highs cross over from V1, I put a darker-sounding JJ 12AX7 in that position, which rounds everything out nicely.

My Vox AC15 on the other hand, is a 2-channel amp with 3 preamp tubes. V1 handles the Normal channel and V2, the Top Boost channel. Vox amps are known to be BRIGHT, which I like but the stock tubes made it sound quite harsh at higher volumes. So basically I wanted to tame the brightness but retain the chime as well. Mullards went into both positions as I find them to be very balanced and musical.

 

[kevchy92]

Hey guys...I don't mean to derail the thread or anything. I have a question to ask. If I change the tubes of my amp, do I need to do extra work like re-biasing?

 

[cobb]

Hey guys...I don't mean to derail the thread or anything. I have a question to ask. If I change the tubes of my amp, do I need to do extra work like re-biasing?

No i doubt u need that. Maybe someone can touch on what is re-biasing and what it does?

So i suppose the 'shrilling' noise from the amp on the C# is normal?

 

[MadWerewolfBoy]

I'm no tube expert but just gonna quote from my textbooks! haha

Technically, bias is the negative voltage which is applied to the power tube’s control grid to set the level of idle current. It affects the warmth of the tone and the dynamic response of the amp.

If an amp is over biased, it will distort more easily, and it'll be hard to get a clean sound. If an amp is under biased, the amp will lack punch and warmth, and the tubes will usually get pretty hot, so lifespan would be shortened.

can get quite an simplified explanation from here:
http://www.youtube.com/watch?v=UM3av6moJd4

 

[cobb]

I'm no tube expert but just gonna quote from my textbooks! haha

Technically, bias is the negative voltage which is applied to the power tube’s control grid to set the level of idle current. It affects the warmth of the tone and the dynamic response of the amp.

If an amp is over biased, it will distort more easily, and it'll be hard to get a clean sound. If an amp is under biased, the amp will lack punch and warmth, and the tubes will usually get pretty hot, so lifespan would be shortened.

can get quite an simplified explanation from here:
http://www.youtube.com/watch?v=UM3av6moJd4

Thanks bro. Kinda understand bout the bias thing now.

 

[CyanideJunkie]

Hey guys...I don't mean to derail the thread or anything. I have a question to ask. If I change the tubes of my amp, do I need to do extra work like re-biasing?

If it's cathode bias like most preamp sections are, then there's no need. However, some power sections are fixed bias therefore a re-biasing is always recommended after a re-tubing in order to maximise your tube's lifespan.