What do you guys see for tonal difference between the two. I have a Carvin MTS amp equipped with 6L6's and a bias switch and I was thinking about trying out some JJ EL34's just for fun and was wondering what to expect.
I switched out the tubes in my Mesa Boogie from 6l6s to EL34s. The 6l6's were the stock tubes, and as such the amp had the signature dual rectifier sound. The high gain settings were just exactly what everyone knows these amps for. The EL34s made a huge difference in the midrange of the amp, and my boogie sounds way more Marshall-esque now. The high gain is where I notice the difference the most. With the 6l6s there seemed like there was almost no limit to just how high gain this thing would go. However, that is not really my thing, and the more subdued, but much more musically and harmonically rich sound of the EL-34s suits me much better. All that being said, I know that Mesa Boogie sells tubes that are tested to fit into very tight tolerances, and different brands of tubes, and which amp you stick them in are going to give you vastly different results. And to answer the last question you asked, neither of these tube sets gave me a lot of unwanted noise, however the overall volume of the amp seems to have decreased a wee bit with the EL-34s. This is all just my limited experience in a single amplifier and with tubes that were all manufactured by a single company, so while this was an A/B type of situation, it is very limited in scope.
Well, 6L6's can be 25 or 30 watt max dissipation tubes depending on the model. This causes much confusion about 6L6 tubes and the data sheets and so on. EL34's are 25 Watt max dissipation. Not sure if this is responsible for the louder part, but I tend to see 6L6GC's (30 watt) tubes in the 120 watt amps.
If you can use EL34's in your amp, I would suggest trying JJ Tesla KT77's. They are drop in replacements for EL34's. In some respects the Mahogany vs Korina comparison applies here. The EL34's are darker and warmer, the KT77's have a bit more bite to them. I found in my amp that the EL34's were a bit muddy for my tastes and the KT77's were the ticket for me. Oh yeah, while the KT77's are drop in replacements, I don't want to mislead you, you still need to bias the amp if you get a set.
The 6L6GC being 30watt.... really a bit of misnomer, because it is - only in UL output amps, of which most guitar amps are not. The last big monster silverface Fender amps were, and are noted for their brittle tone, and terrible breakup. They do excel at "clean" though. So if you see a 60w Super Reverb (with no rectifier tube) or the same thing as a Bandmaster Reverb (MUCH rarer), or 135w Twin Reverb, or Dual Showman or Super Six Reverb or Quad Reverb.... dont expect it to break up at all in any sort of nice toned way.
The analogy for the breakup in these amps is like wanting some 4-wheelin fun on an old washboard road, and finding that you just fell off the edge of the Grand Canyon.
And they cant be changed back very easily or cost effectively.
There IS a good, no.. EXCELLENT tube out there for high wattage on the 6L6 pinout. Its the 7581. Those are like super-6L6's, that use the same everything - same bias, same heater current, etc etc, but with larger beefier plates and cathode. They were able to do this by holding very tight cathode-to-heater distance spec, and just generally upping the quality and keeping things really close together in the tube. The tube is built like a set of bolt on boobs on a fashion model. Solid and there! Expect to pay out the wazoo for them, but they're the top dog if you want clean, but good tone, in your 6L6 powered amp. That is, if you want to play bass through your Dual Showman (a wonderful amp for bass BTW), pop in 7581's and those low notes wont be a problem, because the amp has the iron for it.
-CB-, what do you think of 5751 for 12AX7s? I put one in the third slot of my preamp on the recommendation of a coworker. Makes the preamp distortion nicer in my opinion, though I can't get it as saturated.
ah.... ya know the 6751, 12AT7, 12AY7, 12AV7....and my fav, the 12AU7, its whatever works and sounds as you want it to in your amp.
Some of the nicest toned tubes I ever heard, were the EI made (Serbia) 12AX7's, IF, and only IF you can find quiet ones. OMG... nice nice tone. Nobody like 'em because you had to buy like six or eight to get a quiet one, but when you got it, it was nice. What to do with the noisey ones? Use them in Vibrato oscillators, where noise doesn't matter. But still, thats a lot of vibrato tubes.
There are a lot of good tubes out there today. Find some EI or RCA (the JAN Philips are a bit brittle, maybe shy from those) 12AU7's and try them in various locations. Generally, they'll sound really nice if used in the 2nd stage or later, and get driven with a fair amount of signal. Similarly, as a phase inverter they sometimes let you crank up there a bit. Not quite so nice as a reverb driver, since although they can handle the current, they just dont have the oomph to drive the reverb hard. If your reverb is ungodly though, they'll tame it right down.
You can't really predict the exact tone - to many variables. Goin in knowing that such and such tube is lower or higher gain, is a good thing, and lets you make educated guesses. Still... you have to try and see.
Just to add to the discussion, what about a KT77 as a replacement for EL34 or 6L6's. I play a Peavey JSX, which comes with EL34s, but has a switch to use 6L6s. The guys at Eurotubes claim that the KT77 is the hot ticket for this amp. In general, how does a KT77 compare to the EL34 and 6L6?
What qualities do different 12AX7 tubes (or their compatible replacements) have when switched around in your preamp. I haven't done much fiddling around with my amp, just with guitars, but now that i've got a coupole warmoths that i love, i'm looking into toying around with different tubes and such.
Just to be technically correct, the KT77 is a replacement for the EL34, not the 6L6. For me and my amp, I was able to test it against an EH EL34, and bias them to the same point. I found the KT77 to be not be as dark, a bit more definition. It was closer to the sound I was going for. Not as smooth, a bit angrier. I think that trying to describe this will unfortunately be like trying to describe the difference between preamp tubes, hard to do without trying them your self. I got mine here, but this place has a description of them at the bottom of the page. It is a sales pitch but...