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(@daphnebluestrat)
Active Member
Joined: 18 years ago
Posts: 10
Topic starter  

Couple questions about tubes.

First, does anybody know if there is some kind of rhyme or reason to the number of preamp tubes in an amplifier? as in, why would my Prosonic have six, while the Mesa Roadster has six, the Orange Rockerverb 100 has four, and the Blues Junior have three?

Second, what would be the tonal difference, if any, between different power amp tube types, specifically 6L6s and EL-34s?


   
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(@forrok_star)
Noble Member
Joined: 21 years ago
Posts: 2337
 

One thing is the number of channels the amp has. The Meas Boogie has four channels that why it has so many. Other tubes may include ones used for the reverb or tremolo effects. For output tubes, simply put is they sound different when and react to different harmonic's when their driven into saturation. You'll find everyone will have their own reason for liking different tubes. I happen to like EL84's and driving them into a dummyload as a pre-amp.

Joe


   
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(@ricochet)
Illustrious Member
Joined: 21 years ago
Posts: 7833
 

Some car engines have 4 cylinders, some have 6, 8 or 12. Different designs.

You can't make valid broad statements about the characteristic sound of a particular tube type, as the design of the whole amp circuit affects it. Tubes don't really have any tone in themselves. Generally pentode types transition more gradually into distortion than beam power types, but when negative feedback is applied (as it usually is in commercial guitar amps), that sort of stuff goes right out the window and it comes back almost entirely to the amp's circuit design.

Speakers are a lot more important to the amp's sound than tubes are.

"A cheerful heart is good medicine."


   
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(@corbind)
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Joined: 22 years ago
Posts: 1735
 

Speakers are a lot more important to the amp's sound than tubes are.

Very interesting. Could you stab (guess) what percent of the sound is in the speaker compared to tube? Just guess.

"Nothing...can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts."


   
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(@wes-inman)
Illustrious Member
Joined: 21 years ago
Posts: 5582
 

You are BOTH right.

I know this is getting off the original question, but here is a very good article that discusses the difference between tube and solid state amps, but also discusses the differences in design using 6L6, EL34, and EL84 tubes.

Anyway, a very interesting and well written article.

The Cool Sound of Tubes

If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis


   
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(@ricochet)
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Joined: 21 years ago
Posts: 7833
 

That's a good article. It doesn't get into the specific distortion characteristics of guitar amps heavily, but it's a broad survey sort of article. Eric Barbour is a VERY knowledgeable guy whom I respect highly. He's also a very prolific author, and may have other articles out there that get into guitar amps in more depth. Eric has his own company, Metasonix, and likes to explore unconventional circuitry and use "dumpster" TV tubes not traditionally applied to audio equipment. Check out his stuff at: http://metasonix.com/ (He's got a weird sense of humor, so don't look at the names of his gear if you're readily offended.)

Wild stab at the contributions of tubes, speakers, etc. to tone?
Tubes -- 5%
Speaker -- 25%
Rest of the amp -- 70%

"A cheerful heart is good medicine."


   
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(@daphnebluestrat)
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Joined: 18 years ago
Posts: 10
Topic starter  

Thanks guys...I think I'll explain my reason for asking and maybe you'll be able to offer some more advice?

I want to design and build a tube amp head.

My desires for it are as follows:

-one channel

-no reverb

-one "master tone" control, similar in function to that on a guitar rather than specifically "highs" "mids" or "lows"

-one "gain" control, for distortion

-one "volume" control

-60-watt output (if this effects preamp tubes AT ALL? can't see how it would...)

what I'm wondering is, how many preamp tubes would you recommend I use? I'm guessing I won't need 6, but maybe I'm guessing prematurely.


   
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(@corbind)
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Joined: 22 years ago
Posts: 1735
 

Wes, I read the article and my head hurts. (Note to self: quickly drive home from work and crack open a cold one to numb the pain).

Ricochet, that is shocking that (if your stab is right) I could simply replace the speaker in my tube amp and get a "better/more effective" result than from retubing. I just spent $60 on full retube and $75 to have them installed and the amp cleaned up. For that amount a money I could have bought a new speaker and had somene put it in. Totally interesting stuff...

"Nothing...can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts."


   
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(@ricochet)
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Joined: 21 years ago
Posts: 7833
 

That could be done with one preamp tube, more easily with two (one being used as a phase splitter to drive the two push-pull tubes you'll need for 60W output.)

Where you really need to be hanging out and posing these sorts of questions is on the Ampage "Guitar Amps: Design And Construction" board linked off of: http://firebottle.com/ampage/bbs/ (Look for the button labeled "More" near the right bottom of the page), and the forum at http://ax84.com/ I'd recommend buying and studying some old tube era electronics textbooks (cheap on eBay) until you well understand the theory of operation of tube amps, and study the schematics of existing amps, available from places like http://schematicheaven.com/ and ask questions on the boards I mentioned about why things were done the way they were. Designing a new amp circuit and converting it into a working layout isn't rocket science, but you're a lot more likely to be successful if you do your homework.

"A cheerful heart is good medicine."


   
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(@ricochet)
Illustrious Member
Joined: 21 years ago
Posts: 7833
 

Corbind, I'd never spend my money on retubing an amp with working tubes in it. Period. It's not worth it, and it's asking for trouble as tubes most often fail when they're fairly new. You'll get a lot more noticeable differences by trying different speakers. And there are tweaks that can be done on components in the amp that'll have more tonal effect than any tube changes could. I'm not just talking about "bang for the buck," but a lot more bang.

"A cheerful heart is good medicine."


   
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(@wes-inman)
Illustrious Member
Joined: 21 years ago
Posts: 5582
 

Dennis

I agree with Ricochet for the most part, but not completely. I retubed both my HRD and Marshall DSL401 with tubes from JJ and was very happy with the subtle changes they made
in tone. They tightened up the Drive channels on my HRD nicely, and now my DSL401 just
sounds incredible, MUCH better than before. But the tubes in the Marshall were old and may have been going, I don't know.

And at the very least you have a spare set of tubes, which is important when you gig. I always carry the originals with me just in case. So I am glad I retubed for that alone.

Even this new Celestion I dropped in my HRD did not change the tone drastically. But it is different. I can go up more on Bass now without the low end howling or farting out. It did give my HRD a little more of a Rock tone than before. But it is subtle. I like the new speaker more than the stock Eminence. The other guys in the band said the amp sounded a little different as well.

I did a little side by side testing when I put the new speaker in. I ran the Marshall's Greenback speaker off my HRD. It sounded like my HRD. Then I ran the Marshall's DI out into the Power Amp In on the HRD (the Marshall does not have a Pre-Amp out like the HRD). I thought it would make my HRD sound like the Marshall, but it didn't. It still sounded like the HRD. So, from this I would say the Power section of the HRD has a lot to do with the tone.

We are getting away from daphnebluestrat questions.

Have you looked at the tube amp kits at Torres? They have quite a variety, maybe just what you are looking for.

Torres Amp Kits

Not having ever built an amp, and not being that knowledgeable, I cannot answer your questions. I would send your questions off to Torres, I bet they could give you all the info you are looking for.

They have a real nice Champ kit. That sounds a lot like what you are describing, check it out.

Hope this helps,

Wes

If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis


   
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(@wes-inman)
Illustrious Member
Joined: 21 years ago
Posts: 5582
 

Here is Mojo Amp kits.

Mojo Amp Kits

If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis


   
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(@doug_c)
Reputable Member
Joined: 19 years ago
Posts: 397
 

-one "master tone" control, similar in function to that on a guitar rather than specifically "highs" "mids" or "lows"Here's a technical term for the three-tone-knob arrangement: "tone stack." I just learned that one a few weeks ago myself.


   
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(@forrok_star)
Noble Member
Joined: 21 years ago
Posts: 2337
 

Everything in the signal chain is important. Any little change will effect the out come. Building an amp can be a great learning experience. Read all resources on safety. You might even consider taking an amp and experimenting the doing different modifications. Even a few small changes can really change the tone of an amp. A company called THD makes an amp that you can change different combinations of tubes to create different tones. I believe it comes with 6L6, EL34, 6550,KT90,KT88,KT66,KT77 without having to re-bias the amp. Also you can change the preamp tubes 112AX7, 12AT7, 12AU7,12AY7, 12AZ7. it also has a hot plate power attenuator built in.

Some tubes break up earlier than others, some have a tighter overdrive when driven hard. Some tubes sound hard and some sound soft (if that would be the word for it). After spending some time playing with different amps that have different tubes in them you'll know which ones (meaning tubes) you'll like. How all the pieces put into the amp come together is what makes the different amps sound the way they do. I have a number of small custom and home built amps that only push 1 to 2 watts flat out, but connected to half open cabinet with 2x12 celestions you'd think they were big than that. An for tone their amazing.

joe


   
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(@ricochet)
Illustrious Member
Joined: 21 years ago
Posts: 7833
 

Yeah, small amps can sound amazingly good.

"A cheerful heart is good medicine."


   
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