The difference a tube can make

[Enzo]

I don't see it here as much. but over on the PV forum, we get a lot of confusion because the V numbers - which are schematic references - are not in straight 1-2-3-4 order across some amps - like the 5150 series. SO someone refers to tube #2 in the row as V2 when it isn;t.

[BluesDude]

Thanks for the comments. Very helpful.

[Pedro Vecino]

If you compare the effect of changing one (or five) 12Ax7 in a amp with the obtained one by means of raising the gain 6db. in any frequency of a graphical eq, little relevance is going to be. But the tubes handle texture in the sound (timbre), when an equalizer will never do it.
This effect in the texture the spectator is never going to perceive it in the majority of the occasions, but it will compose the element that you then will modulate playing the guitar. A "tactile" experience. And you, depending on the type of texture will play of different form.
Like any other electronic component, the effect is dependent on what the circuit allows and of how it fits in it, but the texture that can generate an ECC83 RFT (it is an example) in certain overdrive circuit you will not obtain it with an ECC83JJ. And articulation and fluency that an real ECC83 Mullard generates cannot will obtain it with one 12AX7EH.
Put five good ECC83 Tungsram in your Peavey 5150 and try to obtain it using tubes of current production. Before that it, you will achieve to make hamburgers with the texture and flavor of the best roastbeef
Sorry for my poor english.
Regards

[BackwardsBoB]

I think your English was very readable and expressive, and your points were valid and important. We may hold hamburgers in higher regard than you do.

I have the best luck just trying tubes. Even the same tubes from the same manufacturer vary quite a bit in gain, and this is especially important in the drive channel pre-amp.

I have really good luck with used, re-tested RCA 12AX7s. They're frequently cheap on eBay. When you do a full re-tube on an amp, the preamp tubes probably have lots of mileage left on them, and you can try them later in different applications. Used tubes are a good option if you're working on your own amp. Even BugleBoys become somewhat affordable.

You do need to be careful substituting a different member of the 12AX7 family (12AT7, 12AY7, 12AU7). The lower gain tubes can drive more current, and more importantly, their bias voltages are generally higher. For example, Carvin drives a reverb tank off the plate of a 12AX7 without a transformer in the BelAir, Nomad, Legacy and MTS. Substituting a 12AU7 (ECC82) with higher bias voltage into the circuit with the stock 220 Ohm cathode resistor boosts the bias current even higher, and can cause the 12AU7 to overheat, threatening the vulnerable heater circuit. If the cathode resistor is under 680 Ohms, beware. Most subs are safe, but the bias current can still change, altering the tube's bias beyond what would be expected from the gain change. I only point this out because lots of sites promote free exchange without caveats. With this proviso, the 5751, 12AT7 and the ECC81 are almost always safe lower-gain substitutes. For higher gain, most vendors will select high-gain outliers for a small premium.

You can get more dramatic results messing with the associated resistors and capacitors than you can with a tube swap, and resistors and capacitors are much cheaper. In the case of the Carvin reverb drive, it's easy to adjust the reverb loop gain with resistor changes.

[Pedro Vecino]

We may hold hamburgers in higher regard than you do.

Sorry! Sometimes one forgets these things... And handling so badly the English, I have very few resources.
I also use 12AX7 RCA. Especially as first tube in the Mesa Marks. His articulation and bite are inimitable.
Regards

[rockin roy]

If you were looking for crisp accurate reproduction then tube shoping would make more sense. In the case of guitar amps you are paying top dollar for tubes that were almost rejected for use in high fi equipment. Most of the qualities you are looking for can be obtained by changing bias, it is just easier to plug in diferent tubes. I think Fender is moving twords useing FET's as the first stage in their preamps to eliminate ground noise and then tubes to provide harmonics later. This is a little hard to accept if you really love tubes but it makes sense.

The orange drop caps. They are mylar. Smash one, unwind the coiled up peice you find inside and pull. It streches like a sandwich bag. They are good caps and cheap to make. You can pay big bucks for them if you want but it doesn't change what is inside. The reason they are replaced with polycarbonate (it doesn't strech and is more like celephane) is it retains a small charge after a signal goes to zero. I don't think you will hear it. The absolute best choice would be a tefelon cap (if you know someone who works in the space industry). I would replace the monoceramic caps and electrolytic caps if you find them in the signal path.

If you realy want to do the most to eleminate noise get away from carbon, use metal film. Cerimet pots are your best choice for low noise but are linier. Get one that is much higher value then you want and then put a metal film resistor in paralel with the wiper that is closer to the value you want. It wont be a log taper but it might be usable then.

Now the disclaimer. This is stuff I've sold to people who like to expiriment with this sort of thing. I personaly like things the way they come out of the box.

[Ward]

Well seeing as most of this thread is discussing pre tubes, I'd like to put my 2Cs worth in about power tubes. I build Marshall clones mostly and so obviously they need tubes.
For the past few years I've been buying used old stock EL34s, hooked on the idea that they are better, not only sound wise but reliability wise as well. Lately I've had an about face on these old tubes, I will say that Mullard XF2s are the best I've played, in saying that, the difference is both subtle and profound depending on your ear, taste, expectations etc.
A couple of years ago I was working on a friends old Fender showman, 4 x 6L6 amp. I talked him into buying some NOS power tubes for it, he did, they cost him an arm and a leg, when he came around to check out the amp we first off played the amp with the old tubes then put in the NOS, we both agreed that we could not hear one iotas difference. I felt great for my friend here.
That should have said something to me but no, I was still in NOS mode. They are hard to quit.
Yesterday however I think the penny has finally dropped, I was putting a new and supposedly superior OT ( output transformer ) into one of my 100W Marshall clones, as I biased the amp I discovered one tube was dead and the others had drifted all over the place, this was a 1980s NOS set of Tesla EL34s ( not JJs ) that cost me heaps and had only about 5 hours on them, they were gone, all I had in stock was a new set of JJ EL34Ls so I put em in, I couldn't believe my ears, they sounded great, so much better than the "better" tubes, sooooo much better. Now obviously seeing as one of the Teslas was dead you would expect some improvement with a new set even if they were JJs right? Well that being true I must say, the Teslas to my ears sounded the same from day one, so now I have come full circle as far as power tubes go, I started out with JJs years ago, have been forking out rediculous amounts for old stock and now I am finally back where I started.
Unless I get a good deal on some Mullards, yeah right, that'll happen soon, I won't be throwing any more dough away on old tubes. For the price, I think JJs are the go, next would be =C= another good sounding tube but cost 30% more, then nothin. AND, at volume it's even harded to hear a noticable difference, throw in a pedal and whadiya got.
I will say though that I still prefer old pre tubes over new production but the difference for some may be slight at best? It depends on the price of the old tubes whether they're worth it or not IMO. Tweaking amps, whether it be swapping out one brand of cap for another, or using CC or CF resistors, or swapping out tubes, it's all very subtle, of course, it does add up and for someone who can actually build an amp I think it's all for the better but for the guy who just buys an amp and then thinks a new set of tubes will improve it, mostly this will only be the case if there is a bad tube in there to start with, of course, this isn't the case for everyone but on the whole, I'd say NOS is an extravagant venture for power tubes. Just my opinion after wasting so much on them. Far better to get the best speakers, the best pickups, a good lead etc etc than throwing money away on old tubes.

[rockin roy]

As a kid I helped repair TV's (yah, a long time ago). Most often my job was to walk a grocery bag of tubes down to the drugstore to test on the tube tester. I'd end up with a pile on one side that really moved the needle and a pile on the other side for the trash. In the middle there was always a little pile of tubes that were not good enough to keep or bad enough to toss. I wonder where they ended up?

[Ward]

Yep, that sounds like the mongrels I been coppin.

[Danelectron]

I built a 5f2-a awhile back and have been using it to compare 12ax7s specifically. So far I have acquired some telefunkens(rather pricey) , bugle boy amperex(rather pricey) , RCA(ditto), GE, sovtek, Valvo, Tungsol(current production, I got a good deal on a wad of these to use to fire up first trial new builds), mullard and raytheon, sylvania etc.. These are mostly NOS as advertised. My observations are that there is quite a difference between these brands in the only preamp position this amp offers, but I'm happy to say I like them all. There are also subtle differences within specific brands as stated by someone earlier.
The best part of this is that it's fun to experiment. I found temptation to cut out of work to check the mail for an expected tube. I have one Valvo that breaks up really radical. I don't know if it's a defect or what, but very reminicient of Niel Youngs Live Rust solo on Out of the Blue(or Into the Black, The more violent sounding one). This tube exhibits the most varied tone from all the others. Kind of limited (in a super good way), but it definately will have it's place.
Another good point is when you find ones you like for whatever tone, it's almost as easy as pushing a button to use them.
One bad point is that like building amps, you get very addicted. You look up one day and theres flippin' tubes everywhere. I had to move some of my amps to make room for them.
Final footnote: The Tungsols that I bought so I wouldn't have to blow my expensive purchases sound good too. Now I'm on to testing current production tubes.

[FXA]

You do need to be careful substituting a different member of the 12AX7 family (12AT7, 12AY7, 12AU7). The lower gain tubes can drive more current, and more importantly, their bias voltages are generally higher. For example, Carvin drives a reverb tank off the plate of a 12AX7 without a transformer in the BelAir, Nomad, Legacy and MTS. Substituting a 12AU7 (ECC82) with higher bias voltage into the circuit with the stock 220 Ohm cathode resistor boosts the bias current even higher, and can cause the 12AU7 to overheat, threatening the vulnerable heater circuit. If the cathode resistor is under 680 Ohms, beware. Most subs are safe, but the bias current can still change, altering the tube's bias beyond what would be expected from the gain change. I only point this out because lots of sites promote free exchange without caveats. With this proviso, the 5751, 12AT7 and the ECC81 are almost always safe lower-gain substitutes. For higher gain, most vendors will select high-gain outliers for a small premium.

What about a 12au in v3 of the Blues Deluxe. Is there a possibility of overheating. I've been advised by many that there is no problem. it doesn't hurt to have another opinion.

[MWJB]

The PI tube is usually more tolerant to lo mu tube subs, as the tube draws more current, plate voltage drops & dissipation accross the plate resistor rises, but also cathode/tail voltage rises to with respect to ground...evening things up a little.

If you are concerned, measure voltages at the PI node, then pins 1 & 6, then subtract the voltage at pin 8 from previous measurements. Square the voltage drop accross the plate resistors & divide by their value in ohms to get W dissipation...theoretically should be under 0.25W to be "safe as houses"...but be aware that plate resistors in modern Fenders fail anyway, even with a 12AX7...so I'd say use the tube you like best & if a plate resistor fails sub it for a better quality 1W job, there's no guarantee it will last forever with a 12AX7 anyway.

[FXA]

Great and complete answer. Since I am not an amp tech I like the second part of the answer best. It is a 1/2 watt resistor.

[daz]

My experience is that tubes CAN and sometimes do make what I at least consider a big difference. Put it this way....from the worse to the best (from my ear's perspective as to whats worse and whats best) the margin is wide enough that i might sell an amp for how it sounds with the worse tubes in it, yet might consider it a very good am,p with the best in it. I do agree with Enzo in general tho, which is to say the majority of them are close enoufg so that most people won't hear the diff or won't care.

As an example, if i HAD to use only the new tung sol 34's in my amp i would have to start using a different amp. With EH or several others i find my amp absolutly bonerific. There is that much difference to my ears between those. As for preamp tubes, i don't find as much difference as i do with output tubes, but enough that i can be somewhat disappointed in my tone with certain ones. But i could still use those and be relatively happy.

There is no yes or no answer to whether or not tubes make a considerable difference. What it really comes down to is the individual and how sensitive they are to tone and feel and what thier expectations are.

[lassoharp]

I think it helps to think about this subject in terms QC and economics. I don't think the modern production plants can afford to pay sorters what they were paid 60 years ago and I doubt they can afford to keep their overall QC at the same level that giants like RCA and Western Electric could in their heyday. Poor performers came off the assembly line in 1945 and 1995. The modern market for tubes is a fraction of what it used to be and for all the plungers there's plenty who love the idea of a 'matched' quartet of 6550s at bargain bin prices. If someone is willing to take a chance on a Chinese special that costs 1/8 as much as modern premiums or NOS then it makes sense for a manufacturing facility to crate those up for sale instead of what may have happened to those same tubes in a different era - crush them.

If some tube hawk has ten cases of a tube nobody would give a buck and a quarter for one day and within a week the market jumps to $50. apiece - count on hearing more marketing copy filled with just the right set of adjectives most seekers want to hear. The reasons behind the boom can be complex. Maybe a grain of it is based on some real world valid performance observation. Once it gets past a certain point the chasing mentality takes over and for some - I honestly believe there are those who simply choose to spend exorbitant amounts on whatever is currently top dawg on the must have list just so they can say they've got it - pure prestige buying. 800.00 for a piece of glass that has a tax value of 2 pennies.

And lastly, a little pyschology. When someone drop 300 bucks each on some NOS 12AX7s and sticks them in their Marshall . . . they have to sound good if you know what I'm getting at. When faced with the reality that $900 worth of preamp tubes doesn't really sound that much better - if at all - than any of the dozens of modern X7s they've already 'experimented' with would be a hard egg to swallow.

I do think there is some validity to the assertion that some NOS power tubes can withstand higher plate voltages than some modern equivalents, but I see that as more of a QC/ durability issue than tone or sound quality.