Tubes - Fact and Fiction

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Tubes - Fact and Fiction

Postby oddioguy » Thu Jul 20, 2006 9:03 am

I think that some information regarding vacuum tubes is in order. With the resurgence of vintage (and new) tube gear, there seems to be misconceptions and outright false info floating around.

I'll be posting some facts, dispelling some myths, and as always, feel free to post your questions!
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Postby oddioguy » Thu Jul 20, 2006 7:33 pm

Let's start with BIAS.

There seems to be the most confusion over the concept of "biasing" a tube amp. I tend to blame in part the fact that techs are not taught the concept of tube operation anymore (1982 was the last year tube theory was taught at NBCC SJ, as it was a "dead" technology) so most of the information floating around is the equivelent of learning sex ed on a street corner.

Firstly, "bias" refers to a negative voltage which controls tube operation in an "AB" or "Push-Pull" output configuration. This pretty much encompasses most common amplifiers.
If you own a "Class A" tube amp, skip this post and go look at my service pix.

Proper biasing is essential to achieving the most efficient operation from your amp, but is not voodoo.
Too little bias voltage, and your tubes will run hot, shortening their life. Too much bias voltage, and you will experience "crossover distortion", a nasty clipping. The "right" bias becomes a trade off between these two.

You do not need to re-bias if you change pre-amp tubes.
You do not need to re-bias if you change output tubes with similar output tubes.

Typically, the bias is set at the factory and should not need to be tweeked for years, unless you do radically alter your choice of output tubes.
Time will change electronic component characteristics, so eventually the bias may change enough that you can hear the difference in your amp.
The exception to the rule is, if money is no object, running a lower bias voltage can increase desirable power amp distortion. Just be ready to change your tubes often.
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Postby Malcolm Boyce » Thu Jul 20, 2006 8:34 pm

Is there anything to the colour of the glow of tubes indicating their health or proper setup?
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Postby oddioguy » Thu Jul 20, 2006 8:41 pm

You're refering to the purple glow?
That is normal in almost all tubes, but yes, an increase in that glow can indicate a weak tube. It's not a hard and fast rule. Let your ears tell you whether there is a need to replace.
If the plates are glowing red hot, on the other hand...... :twisted:
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Postby oddioguy » Sun Jul 23, 2006 7:09 pm

Lately I've been hearing that some people are warning purchasers of tubes to never touch the glass with thier bare fingers.
This has only started happening since the same warnings began appearing on halogen and xenon light bulbs.

Rule #1 - Tubes are not light bulbs.

Look at the filiment in a xenon bulb. I'd describe it as "white hot". Plus, the bulb itself is filled with xenon gas, which among other things, helps transfer heat from the filiment to the envelope.
It's true, skin oil on xenon or halogen bulbs can cause hot spots which shorten the bulbs life.

The filiment in a tube glows dull orange, producing far less heat, and it functions within a vacuum. Putting sound aside, I've seen tubes function for 30 or more years that have been handled more times than Madonna.
If that is the "shortened" life due to handling, I think I can live with it.

Personally, I've never worried about touching a tubes' envelope.
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Postby oddioguy » Sun Jul 23, 2006 7:17 pm

I'm posting this link because it is pertinent.

http://www.msnbc.msn.com/id/13145804/
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Postby gamblor » Mon Jul 24, 2006 2:59 pm

great timing for a tube thread to start!! let me give you my dilemma.

i have been in the studio recently with curtis basque recording our band's album. right now, the guitar rig i am using in the studio consists of a vintage traynor yba-3 custom special head going into a vox V412BK cabinet. for some very crunchy/stonery marshall meets vox type distortion, i am using a tech 21 double drive pedal. my guitar is an epiphone dot, with a stock humbucker in the bridge, and a gibson p-94 in the neck. now that im done giving you the background (aka - shamelessly bragging) about my rig, lets move on to the actual question :)

weve just finished recording all of the guitars, and apparently my tone seems to be lacking a bit of life to it. curtis has suggested putting some new tubes in the yba-3, which i believe still has the original tubes in it. from what i hear, this can be an expensive procedure, so before i make an investment i have a few questions.

#1. do brand new tubes make that much of a difference, and if so, what IS the difference?

#2 will the universe implode if i use a different kind of tube other than what is in my amp now? i believe the type of tubes i have now are called EL34's (does this sound right?).

#3 if using different tubes is an option, what do you suggest?

#4 where in the solar system can a person buy vacuum tubes for guitar amps, and how much do they cost?

you seem to know what you are talking about when it comes to these things, so let me know if tubes would be a sound investment or if i should look elsewhere to put my tone over the top (ie. different pedal, guitar pickups, cabinet.... etc)

thanks a bunch! and that was a very interesting article you posted by the way.
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Postby weatherstation audio » Mon Jul 24, 2006 4:32 pm

First off, you can buy 12ax7, EL34's tubes etc... from Thom (aka oddioguy) at Munro Electronics... my personal preference of tubes to try out in your type of amp would be Sovtek JAN 5751 tubes in the preamp section and Svetlana El34's in the output section.... if you think you are running the amp with the original tubes, it might be a good place to start ?


Too many variables to pinpoint the possible tone differences in your amps sound.... first off, it's a vintage amp... maybe it needs electronic servicing, new caps etc... is the speaker cab the right choice, check for correct impedence match.
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Postby oddioguy » Mon Jul 24, 2006 4:48 pm

Welcome, Gamblor.
Rule #1 in my threads - Newbie buys the next round! :mrgreen:

To answer your questions:

1) Yes, new tubes can make that much of a difference. They will restore dynamic range, tighten up the bottom end, and bring back the highs.

2) Your YBA3 uses 3 12AX7A preamp tubes, and 4 6CA7/ EL34 output tubes. (6CA7 was the North American version of the European EL34). Althuogh you could theoretically use different output tubes, that would typically require mods made to the amp. Stick with EL34's. There is a fairly broad pallete of tones available by using different manufacturers EL34s, as well as different 12AX7's.

3) Tone is a very personal thing. Sovtek and Mullard EL34's tend to be more mid-rangey (think Marshall), while EH's and Svetlana's tend to be more bottom heavy. 12AX7WA's from Sovtek are fairly bright, while their 12AX7WB's are darker. 5751's (the industrial number for 12AX7's) were the choice of Stevie Ray Vaughn and tend to have a bit less gain. There are more...it's a wide open area.

4) I think Musicstop and Morris stock tubes, and I'm sure that Munro does. Expect to pay between $10-20 per 12AX7 depending on the type, and between $20-40 each for the EL34's, again dependng on type.

Tubes would be my first move with an amp of that vintage (late 60's - early 70's). Perhaps consider having it reconditioned as well. Capacitors dry out and change with age, along with other components. These 2 things can bring an amp back from the dead. Once you have the amp in shape, you can focus on other areas if desired.
Last edited by oddioguy on Mon Jul 24, 2006 8:53 pm, edited 1 time in total.
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Postby Malcolm Boyce » Mon Jul 24, 2006 5:19 pm

Hey gamblor, welcome.

gamblor wrote:great timing for a tube thread to start!! let me give you my dilemma.

i have been in the studio recently with curtis basque recording our band's album. right now, the guitar rig i am using in the studio consists of a vintage traynor yba-3 custom special head going into a vox V412BK cabinet. for some very crunchy/stonery marshall meets vox type distortion, i am using a tech 21 double drive pedal. my guitar is an epiphone dot, with a stock humbucker in the bridge, and a gibson p-94 in the neck. now that im done giving you the background (aka - shamelessly bragging) about my rig, lets move on to the actual question :)

weve just finished recording all of the guitars, and apparently my tone seems to be lacking a bit of life to it. curtis has suggested putting some new tubes in the yba-3, which i believe still has the original tubes in it. from what i hear, this can be an expensive procedure, so before i make an investment i have a few questions.

#1. do brand new tubes make that much of a difference, and if so, what IS the difference?
I have heard many tired amps and pres benefit from a simple tube replacement. It may be oversimplified to say it, but better all around would be the description I would use.

gamblor wrote:#2 will the universe implode if i use a different kind of tube other than what is in my amp now? i believe the type of tubes i have now are called EL34's (does this sound right?).

#3 if using different tubes is an option, what do you suggest?

#4 where in the solar system can a person buy vacuum tubes for guitar amps, and how much do they cost?

you seem to know what you are talking about when it comes to these things, so let me know if tubes would be a sound investment or if i should look elsewhere to put my tone over the top (ie. different pedal, guitar pickups, cabinet.... etc)

thanks a bunch! and that was a very interesting article you posted by the way.
I am very lucky to have oddioguy now hosting this forum. He is a wealth of information, as well as Weatherstation and some of the other "regulars" in this very new little hang out.

Glad you found your way here.
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Postby Alain Benoit » Mon Jul 24, 2006 6:19 pm

Try many different preamp tubes since many cost as little as $10.

You will not find a cheaper place locally to buy tubes than Munro's.

I recently did a 12AX7 shoutout with a tube mic and preffered the Sovtek 12AX7 LPS over all others. Funny thing is that it was one of the cheapest, and the most expensive (EH) was by far my least favourite.

I use WA's in my SPL Vitalizer 9530 and I use WB's in my tube pre.
Oh and Weatherstation just outed Oddioguy.
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Postby Alain Benoit » Mon Jul 24, 2006 6:21 pm

If you decide to recondition your rig do not hesitate to PM me. I have a fully outfited repair/maintenance shop in my studio where this can be facilitated.

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Postby oddioguy » Mon Jul 24, 2006 8:48 pm

U1176 wrote:Try many different preamp tubes since many cost as little as $10.

You will not find a cheaper place locally to buy tubes than Munro's.

I recently did a 12AX7 shoutout with a tube mic and preffered the Sovtek 12AX7 LPS over all others. Funny thing is that it was one of the cheapest, and the most expensive (EH) was by far my least favourite.

I use WA's in my SPL Vitalizer 9530 and I use WB's in my tube pre.
Oh and Weatherstation just outed Oddioguy.

Good advice from U1176.
....and Weatherstation shall be dealt with harshly. :mrgreen:
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Postby oddioguy » Mon Jul 24, 2006 8:51 pm

U1176 wrote:If you decide to recondition your rig do not hesitate to PM me. I have a fully outfited repair/maintenance shop in my studio where this can be facilitated.

(waiting for spank from Malcolm)

Whoa whoa whoa....no spanking! This ain't that kinda thread....
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Postby Malcolm Boyce » Tue Jul 25, 2006 12:14 am

U1176 wrote:(waiting for spank from Malcolm)
You'll need to continue taking care of that for yourself... :-)
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Postby gamblor » Tue Jul 25, 2006 9:59 am

thanks for the advice everybody! now that im well informed on my options, i will definately be out and about shopping for some new tubes within the next week. oddioguy, will you be available at munro tomorrow at around noon? if not... i can make a trip down there some other time during the week.

as far as getting my amp reconditioned goes, i already had the charming Dave Boyer take a look at my amp a while back. When i first got the thing (for free from a friend... omg i kno!!) it wouldnt even turn on. But i gave it to Dave and now not only does it turn on, but it turns ME on!! I dont believe he actually put that many new parts in it tho... so this might be something to consider after the new tubes go in.

thanks for the help.
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Postby oddioguy » Tue Jul 25, 2006 2:22 pm

gamblor wrote:oddioguy, will you be available at munro tomorrow at around noon?

I am out for lunch between 12:00 and 1:00. Other than that, I am here.
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Postby oddioguy » Thu Jul 27, 2006 5:53 am

I was speaking to Gamblor yesterday and he brought up a couple of terms that I take for granted, but which tube-n00b's may not be familiar with. So..a brief explanation:

Matched tubes -
This merely refers to the process of measuring the electrical characteristics of a tube and then matching it to tubes with identical properties. Specifically, output tubes are matched and sold as pairs, quads, or sextets.
This is done because most tube amplifiers use a push/pull output configuration, which is to say that if you were to look at a sine wave being amplified, half of the output tubes are "on" and working only on the negative swing of the sine wave, and the other half of the tubes are only "on" and working on the positive half. Therefore, it is desirable to have all your tubes amplifying in exactly the same way so that waveform distortion is kept to an absolute minimum.

Microphonics -
This term is exactly what it sounds like. Just as a microphone has a diaphragm that vibrates and ultimately produces sound, a tube that is microphonic has a mechanically unstable component which can introduce unwanted ringing and even audio into an amplifiers signal path. You can usually find a microphonic tube by flicking them lightly with your finger while tha amp is on. A dull "thunk" will generally be produced by "good" tubes, while a microphonic tube will audibly rattle, ring, or produce a distorted "thunk".
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Postby thebunk » Sun Jul 30, 2006 11:27 am

Ok my turn.

Hey Thom. I brought a Garnett SessionMan to you about last year sometime. If you recall, the thing would not even turn on and you brought it back from the dead but suggested that I replace the tubes soon.

Well I think I am ready to do this though I have a few questions.

1) The amp has some crackling side sounds come out of it and I am not sure what is causing (def not the patch cords or anything like that as I have tried multiple combinations). Are the current/original tubes in the amp possibly causing this problem?

2) When I turn the amp on it literally takes about 30 seconds for sound to come out. IS this indicative to all tube amps?

3) What type of tubes would you suggest for my amp and roughly how much am I looking at for a set?

4) How easy is it for a noob to replace the tubes?

Thanks in advance for your help.

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Postby oddioguy » Sun Jul 30, 2006 4:36 pm

Garnett Session Man? Don't remember it... :mrgreen:

Image

The crackling can definitely be from the tubes, which were indeed in hard shape. Seems to me I had to replace one of the 12AX7'a as it was dead. The others weren't far behind.

Tubes take time to reach operating temerature, so "yes", all tube amps need time to warm up.

Your amp uses 2 x EL34's, 4 ( I think) x 12AX7, 1 x 12AU7, and 1 x 6JW8.
Plan on dropping $100.00.

Tubes are very easy to install yourself. The only caveat is to watch the power tubes closely for 30 minutes or so after you install them. If the plates start glowing red hot, turn the amp off and have it checked over. The bias may need to be set for the new tubes.
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Postby thebunk » Mon Jul 31, 2006 11:27 am

oddioguy wrote:Garnett Session Man? Don't remember it... :mrgreen:

Image

The crackling can definitely be from the tubes, which were indeed in hard shape. Seems to me I had to replace one of the 12AX7'a as it was dead. The others weren't far behind.

Tubes take time to reach operating temerature, so "yes", all tube amps need time to warm up.

Your amp uses 2 x EL34's, 4 ( I think) x 12AX7, 1 x 12AU7, and 1 x 6JW8.
Plan on dropping $100.00.

Tubes are very easy to install yourself. The only caveat is to watch the power tubes closely for 30 minutes or so after you install them. If the plates start glowing red hot, turn the amp off and have it checked over. The bias may need to be set for the new tubes.


Thats it!

Thanks a lot. So what models/manufacturers do you recommend? Also, do you know of any good sites on the net that show noobs step-by=step how to remove/instal tubes?

Another question (slightly off topic) does Munros carry single button (controlled) foot pedal switches with no LEDs or am I going to have to go to MusicStop? I do not have a pedal to enable the Tremelo effect and would like one.

Thanks in advance. I may be by tomorrow to pick the stuff up.
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Postby oddioguy » Mon Jul 31, 2006 12:20 pm

Web-site? We don't need no stinkin' web-site...
Just grab the tube and pull while gently rocking the tube in a circular fashion.
EL34's ( the big tubes) are keyed so they cannot be inserted improperly. The small tubes don't have an actual key, but the pins are arranged so that they can only be inserted one way.

Yup, I have some footswitches here. Hosa FCS-384 is likely what you need.
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Postby gamblor » Fri Aug 04, 2006 4:50 pm

okay....... i am currently in the process of replacing my tubes and ive got a slight concern

when replacing the el-34's.... on my old tubes, there are pins spaced evenly all around the bottom of the tube. on the new tubes, it is the same alignment of pins, but there is one pin missing where there would usually be a pin on the old one. also, there are numbers on each of the pins on the new tube.

so with this in mind, does it matter what way i insert the tube?
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Postby Malcolm Boyce » Fri Aug 04, 2006 5:04 pm

oddioguy wrote:EL34's ( the big tubes) are keyed so they cannot be inserted improperly. The small tubes don't have an actual key, but the pins are arranged so that they can only be inserted one way.
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Postby gamblor » Fri Aug 04, 2006 5:05 pm

Malcolm Boyce wrote:
oddioguy wrote:EL34's ( the big tubes) are keyed so they cannot be inserted improperly. The small tubes don't have an actual key, but the pins are arranged so that they can only be inserted one way.


ahh okay........ i just realized this.

so its okay that the new tube does not have the same amount of pins as the original?
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