6L6GT vs. EL34/6CA7 and WHY?

[Runco990]

Forgive the dumb question, but everywhere I look, the 6CA7 and EL34
tubes seem to be the same tube. As in EL34/6CA7 in one breath. I do not see anywhere a totally seperate 6CA7 tube.

I thought they are the same. Am I mistaken or are you guys having fun with me?

Marc

[Runco990]

After another intense google session I did indeed find an article that explains the difference between the EL34 and 6CA7, subtle as it is.
You gotta love google.

Never thought I'd learn this much in 2 months going to tubes.

Marc

[anatech]

[Ty_Bower]

To me, when I think 6CA7, I think of the "fat bottle" tubes. Like the (now out of production) Ei Yugo 6CA7, or the Electroharmonix 6CA7-EH.

When I think EL34, I think of a "skinny" tube, where the glass is no wider than the base. More like an EL84/6BQ5 on steroids.

[ray_moth]

The reason why some people like pentodes while other people like beam tetrodes is largely a matter of personal taste and sometimes prejudice or peer pressure.

The reason for the existence of both types of power tube in the first place came about when the beam tetrode was developed to get around a patent that had already been taken out by rival manufacturers on the pentode. Beam plates were found to be a practical alternative to the suppressor grid for overcoming the tetrode 'kink'.

Once the beam tetrode was established, its manufacturers naturally carried on producing it and endeavoured to gain and maintain a good share of the power tube market. The pentode manufacturers did likewise. Hi-Fi amp builders seemed not to be particularly devoted to one tube type or the other, but guitar amp builders were somewhat polarized, e.g. Mashall liked pentodes (EL34) and Fender liked beam tetrodes (6L6).

Pentodes and beam tetrodes do much the same job but are not always plug-compatible, because they have different needs. In general, pentodes can tolerate higher screen voltages and higher values for grid leak resistors than beam tetrodes. This can make pentodes a bit easier to drive. If beam tetrodes are subsituted in amp designed for pentodes, without making any circuit changes, it could cause poor performance or tube damage.

[Cycline3]

Originally posted by Runco990
"It just sounds better" is not enough for me. I need some electronics theory to back this up. Anyone want to take some of the Voodoo out of this for me?

Marc, you're in the wrong hobby then! Tubes will never measure up to solid state. I think you need to take a leap of faith here and realize that for all of our technology - we can't measure the numbers that actually represent what makes one amp sound better than another.

Tubes are constructed differently and with different materials and thus sound different, just like a paper woofer sounds different from kevlar one.

As for 6L6 vs. EL34 -- it is a matter of personal taste. I prefer the EL34 in my guitar and audio amps myself, but others like the 6L6. However, if I had to choose between chinese EL34s and NOS GE 6L6s.... I'd take the 6L6s because they would be a much better tube! Again, tube construction matters! As for choice, there seems to be a good selection of both tubes in production. You can try both in your amp and see which you actually do prefer! That's part of the fun! Let the tube rolling commence!

Probably the best advice I can give you is have patience. Tube amp building and learning is something you really acquire over years... not days. The good thing is, even poor quality tube gear still usually sounds really swell.

Also, one addition as was noted above --- the 6CA7 and the EL34 are electrically equivalent tubes, but not constructed the same. Obviously the plates are completely different -- inside the EL34 is a true pentode and the 6CA7 is a beam tetrode. So while they are plug and play exchangeable... they will sound different!

[Miles Prower]

Originally posted by Runco990
OK, so in an attempt to better educate myself, I thought I'd ask the experts for opinions on this. I did search, but got no real answer....

Fact is: you're not gonna get any "real answers" simply because psychoacoustics includes a considerable amount of variables, and no one really knows what to measure. Look at the specs: 807 Class AB1 has a THD figure of 1.8%, and the 6V6 comes in at 3.5%. So 807s must sound better, right? So how is it that the raves for the sonics of the 6V6 are universal? Some folks have doubts as to how 12AU7s sound, but I haven't seen anyone say that 6V6s sound bad.

I did a project using 807s, and found that the THD spec was spot on. However, running completely open loop, with no feedback of any sort, the 807s had an edgy nastiness in the upper mids and highs that was very annoying and would quickly wear you out. I included both local NFB (indeed, the inventor of the type (O. Schade) recommended lNFB) and gNFB to tame that, and make for a really good-sounding amp.

The latest project was based on the 6BQ6GTB horizontal deflection power final. The loadline for that came in with an h(3) estimate of 5.0% (although it measured more like 3.0%) but still higher than the 807 amp when running open loop. You'd think that the 6BQ6s'd sound worse. However, that wasn't the case, as there was hardly any outright pentode nastiness unless the volume was set too high anyway. For this design, based on what I heard while playing it open loop, I decided to not install any local NFB, and rely on gNFB only to take the edge off the highs, and for improved woofer damping. How does something like this happen? How is it that the "superior" audio VT needs more help from NFB than a type that wasn't intended as an audio final, and whose spec sheet includes no data for audio useage. Indeed, the 6BQ6 sounds like a 6V6 on steroids from what I can tell. Good thing no one has discovered this since 6BQ6GTBs are widely available, and at a price way lower than any "audio" VT, and it can certainly hold its own with the 6L6s/6V6s/EL84s/EL34s/KT66s/KT88s/ad infinitum.

Then you have the whole true pentode/beam tetrode/pseudotriode/triode controversy. The wrangles over topologies (PP vs. SE; Ultralinear vs. parallel lNFB vs. no NFB) Classes, and who knows what else. And that's before you even get to the small signal VTs. I figure that the best thing to do is say "T'hellwiddit" and put that "evil" gNFB to good use for what it was intended to do: make the end performance less dependent on the open loop performance and components.

Sandy amp designers have it a good deal easiler, since there aren't these fusses over transistor or IC types ( and there's a reason for that as well).

[vinylkid58]

Originally posted by Miles Prower

Good thing no one has discovered this since 6BQ6GTBs are widely available, and at a price way lower than any "audio" VT, and it can certainly hold its own with the 6L6s/6V6s/EL84s/EL34s/KT66s/KT88s/ad infinitum.

No kidding, good luck finding a NOS GE6L6 for $2. The 6BQ6GTBs are better looking anyway, with that cool top mounted plate connection.

Jeff

[anatech]

Hi Miles,

Sandy amp designers have it a good deal easiler, since there aren't these fusses over transistor or IC types ( and there's a reason for that as well).

Ahhhh, I disagree.

LOL!
Have you looked at the Bob Cordel threads? There is a high amount of voodoo and snake oil in every audio pursuit. There is even talk of how good the old Germanium transistors sounded in the SS forum.

Then there are the classes and output stage configurations, input stage configurations. It never ends. So, it's about the same as here.

-Chris

[Salas]

Its only that silicon bits aren't tri nippled like Golden Gun Mr. Scaramanga, alight, and above chassis! If you got your snake oil, it better shine on a sultry curve... Heat fins are boring!