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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Fri Jun 11, 2010 11:11 pm 
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BlueAngel: Quite interesting as to what you have to say on the tube topic.

From your experience and opinion, what are some of the "better" tube replacement brands to seriously consider for a Vox amp (AC 15) and what are some brands that should be avoided?
Seriously consider: almost anything NOS, or just plain used, made in the USA or Europe before the mid 1980s.

Avoid: new-production tubes, especially those made in China or Russia.


OK, that's a deliberately huge generalisation! - but I am being serious. NOS tubes may look expensive compared to new-production ones, but if you factor in reliability and life expectancy, many of them aren't - and can even be cheaper in the longer run. And they just sound better too. You don't have to go for top-name brands like Mullard or RCA (although they are great tubes), and you don't only have to buy NEW old stock, lightly-used tubes can be fine if you either get them from somewhere reputable or can test them properly yourself.

If you really must use new-production tubes, JJs seem to be among the more reliable, especially for rectifiers and power tubes, but I've still had failures straight out of the box with them. The Chinese tubes are better now than they were a few years ago, but the power tubes are still very variable and tend not to last long even when they don't fail. Of the Russian tubes, some are better tested than others even though they come out of the same factories... but that only helps up to a point, just testing something does not make it better, it just weeds out the really bad ones... which is not quite the same thing!

Particular ones to avoid: Sovtek rectifiers; Sovtek or other Russian 12AX7s in cathode-follower positions (which includes V2 in the Vox AC30CC - although they're fine in other applications); any Chinese EL34.

Also be aware that the tubes now being sold as "reissues" of famous brands like Mullard and Tung-Sol are nothing of the sort. They are simply modern-production tubes with old names printed on the outside. Some of them do make an attempt to copy the original construction, and some of them even sound good, but the quality isn't there.

If you really care about the tone and reliability of your Vox, it's pretty hard to beat real old Mullards though. If you can't spring for that, other British brands like Brimar and Mazda aren't as expensive and have the right sound - but be careful, because even back in the day these companies also re-labeled imported tubes! Even Mullard did at some times. Some of these import tubes are very good (eg Amperex or RFT), but they don't sound the same as what you might think you're getting...

Yes, it's a minefield. If you don't have the experience to know what you're getting, I would stick to a reputable specialist dealer like KCA or Lord Valve, even though you generally pay a little more.


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Mon Jun 14, 2010 11:47 am 
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Joined: Sun Apr 02, 2006 1:00 pm
Posts: 1957
Location: San Bernardino, CA
WOW!
As you say, a minefield.
I can't thank you enough for your real info. Definitely lots to keep in mind and consider.
Many thanks, my friend! :)


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Mon Jun 14, 2010 7:50 pm 
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To expand on what Blue Angel said, on my Blues Jr I use NOS 5751 and 12DW7 for the #1 and #2 tubes (#2 tube circuit modified with a cathode-follower circuit to take advantage of the other half of the 12 DW7 to buffer the output to the phase inverter 12AT7). NOS JAN are usually good tubes(joint army-navy military spec). NOS, when possible or affordable, are the way to go.

thetubestore.com has a great selection.

If you must purchase new, then yes, JJ has good tubes. Electro-Harmonix also does a really good job of culling out the bad tubes. I have a pair of their new version 6CA7 power tubes (American "big bottle" version which can be used in place of an EL-34 using 6550 plates, but the same bias, so I get a lot of clean headroom) in my Marshall, and it's a really, really "big" sound, and their 12AX7 version is really clean, considering, with low noise. But caveat on their 12AX7 version: the base is a wider diameter, so it may not fit all tube sockets, especially Fender-style with noise cans.


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Wed Jun 16, 2010 3:55 am 
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The Tube Depot tubedepot.com is also a great place to get NOS tubes, but they're not cheap. I just got an email from them today advertising an "18 Watt British Amp Kit," for whatever it's worth -- have your own combo complete with one Greenback for, well (gulps at sticker shock)!!


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Wed Jun 16, 2010 9:03 am 
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Joined: Sat Sep 27, 2008 10:49 pm
Posts: 573
Location: Stanstead, QC
Well, we've covered a lot of ground in 3 pages, from tubes to speakers, and of course, there is no concensus.

If you want to settle the alnico speaker issue for yourself, start with:

http://www.youtube.com/watch?v=jWK0sa7tlfI

Yes indeed, these speakers all sound different, but there is no definitive answer as to which is "best" for everyone. Celestion and Jensen also have decent sound samples of their speakers on line. It remains to be seen whether you will get sick of hearing the same phrase repeated over and over again before you hear the tone you want, even assuming that the sample is relevant to what you play.

As for the solid state/tube issue: which police car grabs your attention most, the one with the solid-state strobes flashing or the older style analog tungsten bulbs actually rotating? I suppose it really depends on what you expect from your police car, and is probably not worth arguing about.

Many of us who grew up in the sixties cut our teeth on analog equipment such as tube amps and vinyl lp's, often played through tube amps as well, so I suppose they seem more "natural" to us, with their rather slow ramp up and down compared to transistors.

I would prefer an approach where you can make the best of both worlds: take U2 as an example, where every guitar note you hear is the product of both analg and solid state technologies.

I'm just glad that Rickenbacker has stayed away from the race to the bottom in manufacturing.


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Sun Jun 27, 2010 6:39 am 
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Joined: Thu Jan 12, 2006 2:00 pm
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Location: Long Beach, California
One reason some AC30s are a pain to change the tubes on is because the speakers are hard wired to the chassis/head, and with too short a length of wire, which makes actually removing the guts of the amp from the cabinet to get at the tube difficult to impossible. I've modded both of my AC30s with the hard wired speakers to have speaker jacks to avoid this issue. It also makes things easier for the tech to perform other types of maintenance as well-maintenance that requires removing the chassis from its wooden sliding tray to get at the components on the underside of the chassis.

The sheer number of screws required to remove an AC 30 chassis/head from the cabinet are another reason! :)


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Fri Jul 09, 2010 11:09 pm 
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Location: Appleton
All amplifiers create distortion at any level. Tubes emphasize even order harmonics while transistors emphasize odd order harmonics.

The ear is much more sensitive to odd order harmonic distortion so it picks up on that readily and identifies it as unnatural or out of place. Also, when pushed hard, tubes naturally compress the signal, easily creating yet more even order harmonic distortion, which still sounds normal to the ear, doesn't call attention to itself.


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Mon Jul 12, 2010 9:42 pm 
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Location: Scotland
Quote:
Tubes emphasize even order harmonics while transistors emphasize odd order harmonics.
Actually this is completely untrue, but one of the common myths about why tubes sound better.

All amplifiers create similar types of distortion. It's almost impossible to tell a single tube gain stage apart from a single transistor gain stage whether it is clean or distorted. For a typical single-ended preamp gain stage (of either technology) there is an equal mix of odd and even harmonics.

However, one of the big differences is that tube amps tend to use output transformers, which in a push-pull design inherently cancel *even* order harmonics (yes, that's right). However, this only applies to harmonics generated by the power stage itself - ones generated earlier, both odd and even, are amplified equally.

Quote:
The ear is much more sensitive to odd order harmonic distortion so it picks up on that readily and identifies it as unnatural or out of place.
The transformer is also tone modifier, which tends to suppress square-wave characteristics (*not* odd-order harmonics, even though a square wave is a Fourier synthesis of all the odd harmonics), which are inherently unnatural-sounding - there's no natural sound generator which produces a square wave, it's something which only exists with electronics - and modify them into something more like a triangular or saw-tooth wave which is inherently more natural-sounding. This is nothing to do with the harmonics generated by the gain components though.

Quote:
Also, when pushed hard, tubes naturally compress the signal, easily creating yet more even order harmonic distortion, which still sounds normal to the ear, doesn't call attention to itself.
This also isn't true. Tubes don't compress any more than transistors - but the more primitive, high-voltage/low-current power supplies in vintage tube amps certainly do, and the cathode bias used in the power stages of many such amps does as well. Transistor amps by comparison tend to use stiffer ('better') power supplies and more constant types of bias so they sound more linear.

If you don't think any of this is correct, try playing guitar through a tube hi-fi amp into full-range speakers (so you can actually hear what those harmonics are doing, unlike with normal guitar speakers) and you will find it sounds very nearly as awful as a solid-state amp... though not quite as much so because there is still an output transformer. If you want to eliminate the output transformer too, you can DI the preamp of a standard guitar amp... and listen to the harsh "transistory" distortion.

The transformer isn't the *only* difference either - you can build a solid-state amp with one, and it won't magically sound like a tube amp, although it will sound better - but it's the combination of all the circuit elements and characteristics working together that make tube amps and solid-state amps sound the way they do, not to do with which harmonics are generated by the active components.


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Wed Jul 14, 2010 7:24 am 
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Yep, what BA said. The odd order harmonic myth comes directly from the Fourier square wave synthesis and the fact that transistors, when driven into clipping produce a flat topped waveform rich in odd order harmonics...


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 Post subject: Re: Tube amps-Your info and thoughts?
 Post Posted: Thu Jul 29, 2010 7:55 am 
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Joined: Wed May 05, 2010 12:47 am
Posts: 66
Location: Kansas City
Back in my younger days, I worked for a magazine dedicated to audio and video installation and systems design. We ran a pretty cool article on audio perception and the psychology of hearing. When it comes to what we hear organically vs. digital, there is a difference when it comes to recording (at least the article states). CD audio, I believe, limits what is recorded and reproduced to the scope of human hearing 20Hz - 20kHZ. Although we cannot hear sounds outside that range, the author posited that we can perceive them as harmonics of tones that do lie within the range of our hearing. A tone recorded and reproduced without those harmonics would sound thinner. Hearing a symphony in a concert hall, for example, would enable us to perceive those harmonics and yield a richer audio experience; hearing a CD recording would not. The author went on to theorize that analog recording and stereo gear preserved more of those harmonics. Not sure how much of that applies to the current discussion, but I always found that interesting.

Personally, I used to play through an old mid-grade solid state. I eventually traded that for credit toward a mid-grade tube combo amp and later bought a '65 reissue of a classic amp. Personally, I prefer tubes. I know it's not fair to compare the much more expensive classic reissue to the mid-grade solid state, but the first time I fired that amp up, I just felt at home. My Ric just sings through it (as do my other guitars). Such brightness and sustain, and that overdrive is just plain heaven. Granted, I have to crank it pretty loud to get that overdrive. There are ways to get that down with some minor amp modifications, but I don't mind annoying the neighbors. In fact, it's my way of retaliating for all the power tools and lawnmowers I hear early weekend mornings.

But I digress...

I know tubes are a pain. Replacements vary widely in quality, and replacements/maintenance can be a pain. After switching tubes, reacquiring the exact same tone can be a futile nightmare. That's ok with me. I don't need that total level of control over my tone, and I'm happy to turn over some of that control to my amp and guitar. It's kind of like organic versus digital photography. Sometimes the random organic unanticipated variables lend a degree of character and life to the art. Whereas something built from the ground up in the digital domain might lack that life were I to build it myself. I need some randomness to give my music dimension and life. Others, however, may not, and that's perfectly cool. Maybe I'm just a lazy (you said bad word).

Anyway, apologies for the diatribe here. Just my two cents.


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