What do these tubes sound like?

Amplifier design is more critical, as are the transformers.

However, the tubes listed in your query are so different that you can discuss the issue because you don't normally find 6550 based SET amps or more modern amplifier topologies using the 300B.

300B: The over the top strength of this tube is its midrange. Treble is severely rolled off. As are the lower frequencies, which are the very definition of loose. Many people feel that the tube's magical midrange is actually a result of a high degree of overexaggeration. In a circuit designed to use a variety of tubes, this is the common feeling. But oh, when things are right, these tubes produce a lovely sound. Very immediate, lifelike, coherent, with a natural warmth and glow that solid state amplifiers cannot dream of reproducing. Moreso than with a lot of tubes, the 300B, even when used in a non SET amp, is quite dependent on the amplifier's transformers and speaker load.

6550: I should preface this by stating I am not a fan of this tube. In my opinion, I don't see much reason to use it, other than availability and some companies like Audio Research saying that it should be used in a retube of many of their amps. I feel that if you want a classic tube sound, use KT88s. If you do not want a classic tube sound use KT90s, which do everything that the 6550 does well even better, coupled with a more listenable and natural midrange. I find the sonics of this tube to be lean and forward; the antithesis of lush. Amps using this tube have often struck me as edgy, unnatural, dry, and lacking warmth. I often felt that owners really favored solid state sound, but revel in owning a tube amp. Most of the time, all of this was corrected by mere substitution with KT88 tubes. The strengths of the tube are its extension at both frequency extremes, stability, reliability, power output, and tube life. Given the choice, I opt for a good solid state amplifier over the 6550.

EL34: Sunny and warm midrange. The sonics in general are warm, lush, and full bodied. This is the tube which most people are thinking about when they talk about classic tube sound. Mostly because it's a tube that was featured in so many classic tube amps(Williamson circuit[which so many tube amps copied or modified], Dynace ST70, Marantz 8/8B/9, etc.). The strengths of this tube are its midrange, liquidity, richness, and non - fatiguing sound which immediately puts most people at ease and can listen to all day long. The bass is loose and not normally so well extended, and the higher frequencies are not as open and crystalline as they probably should be. Those who are into "accuracy" at night probably dream of ridding the earth of the EL34.

6C33C-B: I guess I should list the negatives of this tube before its strengths. The negatives are... Um, well, uh. It's not a widely available tube. Who knows how easy it will be to find 20 years from now, but hasn't that been the story of living with tubes over the past 25 years? It's also pretty expensive for new stock. Further, I believe it's manufacture is in Russia only, as a military tube, it may even be discontinued. It's operating conditions would incinerate other tubes, which would only be a consideration if one needed to switch to a different tube in the future. That's about it. It's strengths seem to be every thing other than what I just listed. It's bulletproof, stable, supposedly lasts a LOOONNNNGGG time. The tube has great power, bass, and extension. Midrange is lush and warm(I guess these would be a negatives to some), and very natural and musical. Highs are open and extended, but airy and smooth. In many listening experiences, I have first said "Wow!", then looked down to see this tube in the amplifier. Natural, musical, relaxed, and effortless have always been the case. Would I be out of line to say that if a tubeophile dreamt up the ultimate tube, this is probably it. Someone could probably rip my description to shreds by saying that amps and companies that use this tube are the creme de la creme.

Hey Trelja, thanks for taking the time to write up such a great description of each tube!! very helpful!

I completely disagree with the assessment of the 300B. “Treble is severely rolled off. As are the lower frequencies, which are the very definition of loose.” The performance of a tube at these frequency extremes is a function of amplifier design and speaker interaction much, much more than the tube. Amps using the 300B can and are designed that give a frequency response well beyond the range of human hearing. I recently sold a Wavelength Duetto 300B SET amp that was -3dB at 15 and 45,000 Hertz. Before that I had a VAC 30/30 that was 8Hz-85,000 Hertz -3dB. If this is a severely rolled off top or bottom end then I don‘t understand what those terms mean.

The loose bottom has more to do with the typical low power of SET amps and poor speaker selection, not the fact that a particular amp is using a 300B. Higher power push-pull 300B amps like the VACs have just as much or more bass control as any other amps of comparable power. If you use a low power SET 300B amp with a low efficiency speaker, you may well have a loose bottom and rolled off highs. Matched to an appropriate speaker they will perform as well or better than any tube out there.

They do have a glorious mid-range.

Herman, you make some good points. I did preface my statements with a line about amplifier circuits and transformers being more critical than the tube itself.

I agree with your statements about the VAC. However, their use of this tube in this manner is definitely in the minority, which is what I meant by not normally using the 300B in a modern amplifier topology. The vast majority of companies use the 300B in an SET amplifier. Kevin Hayes is a genius, and this line of amps of his are the proof.

I also said that the tube is more dependent than most tubes on both the transformers and speakers it is matched with, which you reiterated.

Still, I maintain that the treble and bass are reigned in. That's because in 95+% of the amps in which it is employed, that is what the tube sounds like. Which is the question at hand in this thread. Wavelength and VAC are among the best of tube amps, and Gordon Rankin and Kevin Hayes deserve commendation for their elegant products. How about when Audio Electronic Supply, Antique Sound Labs, Cary, Golden Tube, The Parts Connection(defunct), and the myriad less expensive companies that execute a 300B based amp? Do you think you'll see the same specifications that you listed?

Anyway, I don't really want to get into specifications when it comes to 300B tube amplifiers. Measurements on tube amps, and SET amps in particular do not cast these products in a good light. Normally, their specifications never look as sterling by anyone outside of the designer. Often, they fall apart like a cheap suit when subjected to testing that a horrid sounding mass - fi product aces. Like all amps, what you see through an 8 Ohm dummy load will be far different from what you see when you actually drive anything like a speaker. I don't listen to dummy loads, and I don't know many other audiophiles who do. I listen to music, that's where I base my assertions.

I respect the bass that VAC can produce with the 30/30, but did the Wavelength sound like it could do -3 db at 15 Hz when you listened to it? I have never heard the Duetto, but neither the Cardinal nor the Gemini I did hear would ever make me think about 15 Hz. I really like Wavelength products, but I wouldn't be buying one of their amps based off of the bass that they put out.

Compare the 300B to the 2A3 in the same amplifier circuit, and I maintain that despite the 2A3's decrease in power output, the lower frequencies will be more powerful, more extended, and more tight. I also feel that a similar, but not as pronounced effect will be noticed in the higher frequencies. The 300B will have the edge in what you so rightly stated as a glorious midrange.

I thank you for the provocative and interesting discussion. It's great to talk about tubes, a VERY personal topic.