The world headquaters of the World Wrestling Federation is only a couple of miles from my home, and because of the prominent position I play in the local Stamford, Connecticut community, I was invited to their annual Christmas Party. Of course Hulk Hogan recognized me in my kilt and tube hat, and immediately pushed through the crowd surrounding me to get my authograph.
Let me pause for a moment and tell you something you probably didnt know about Hulk. Hulks doesnt buy his motorcycles or audio equipment off the shelf. All of his motorcycles are custom, which are Hawgs, are custom made for him. He has a responsibility to inspire his fans. Same is true for his audio equipment; he has become so refined musically that all of the compromises inherent in store bought equipment simply will not due.
So the first thing that Hulk asked me was about his single-ended triodes. It seems that for decades Hulk was using some very high horsepower solid state amps, and quite by accident when he heard a 300B SET he felt that someone had just hit him over the head with a chair...but the Hulk wanted and needed more triode hulk, so his questions were all about...how do I get more of that triode cream?
I find it interesting that Hulk Hogan is so tuned into the same vibe of our community where more and more men after hearing a 300B are saying...more, give me more...which is what real men say when ever they taste something they like.
The problem at the time was that I couldnt really answer the Hulks questions because the video crews of the local TV news needed to interview me, so I told Hulk that I would email him my latest thoughts on the subjects of triode power. I have posted my email to hulk on my web site for the benefit of all.
It was great meeting you, and as I promised I am sending you my latest thoughts on higher power directly heated single ended amplifiers.
So you heard your first 300B SET amp and you want more...you want that same five watt delicate aroma at fifty watts . I recommend you study Nobu Shishidos book on this subject. Nobu dedicated his life to this search for power while preserving refinement and pioneering a new single-ended pathway to power using large directly heated Class B RF transmitting tubes. And Nobu consistently broke the horsepower boundaries in this genre of amplifier. As you know his 100 watt WAVAC SET amplifier uses the 833 "cookie jar" tube. My long term experience with his 50 watt 805 amplifier was very heavy rock and roll cream indeed.
Hulk it is quite understandable when you see these large Class A and Class B triodes you are in awe of their beauty. No tubes are more totemic and totally phallactic. Some of these tubes glow so bright they literally light up a room like a light bulb. And the reality for us all is that because the Priests of the American Temple of Monkey Coffins have the creative vitality of the Communist party with their low effeciency ethic, gifted listeners have no choice but to procure higher powered directly heated triode amplifiers.
First let me discuss tube choices:
CATEGORY ONE: Classic industrial/transmitter tubes: What is cool about these tubes is that, unlike audio tubes, these tubes were designed for long term industrial use. They are rugged, well designed and will not need replacement for years, decades or a lifetime, depending on how you use them. Many of these tubes are used in small radio stations, air force bombers, or some weird industrial application, and have been around since the 1930s. The 833 tube that is in the WAVAC amplifier appears in an 1933 RCA tube manual! The 845, 211, 805, 838, 811, and their variations are heavy duty mothers. Though no one is yet certain, Western Electric, may be producing the 308 tube which was used in a gigantic audio amplifier on aircraft carriers. This monster tube has the right electrical characteristics for a completey on the edge amplifier, and Cary audio has already demonstrated the first amplifier using this tube. Both in Japan and America this tube has also been exploited by the DIY crowd because what could be better than 13 inches of hot glowing triode? These tubes were never really intended to be used in home audio amplifiers, which proves how really cool tubes are at adapting to changing times.
CATEGORY TWO:The Kron Category: Two days ago I was awakened by a call from Count Kron telling me that he was going to debut at the CES three new high powered directly heated triodes include KRONZILLA...the worlds first superhero tube. As you all know the current range of KR tubes including the KR 52 is leading the directly heated triode race in terms of power with refinement because they DONT NEED 10K transformers. When you surf the web both the 300BXL and 52 are the triodes of choice for those seeking more of that triode cream.
But there are four challenges facing the implementation of high horespower single-ended directly heated triode amplifiers:
1. OUTPUT TRANSFORMER LIMITATION: Designing a modern a single-ended output transformer is not easy, and much more difficult than implementing a push/pull transformer. Without getting technical...think of this type of transformer as your drag racer, which has its engine revved up on the starting line, so that when you pop the clutch, and accelerate you dont get bogged down. Now there is a limit to how much you can rev up your engine while you are idling or you will destroy your engine, and that is the problem facing higher powered SET output transformers which require more bias (idle) current, which means that the magnetic gap has to be bigger which is more problematic. It is usually the case that these bigger triodes require a 10K pirmary impedance which is three times as large as the "normal" 3K impedance (used with a 300B), which translates to a larger turns ratio, a bigger transformer stack and a multiplying of all the forms of transformer distortion that corrupt the signal.
The smaller output tubes sound like they have better transient response, more air, delicacy and life because, in effect, a transformer while transforming is also filtering, and a smaller transformer will do less damage to the whole-osity of the music signal than a larger one.
What this means is that if you are going to use a phallactice triode, the quality of the output transformer is much more critical, and more expensive.
2. DANGER: These bigger classic triodes need much higher voltage 800 to 1300 volts power supplies and that can be pretty scary and expensive because high voltage capacitors are much more expensive, and high voltage tube rectifiers are also very expensive. DIYers who want to live long happy lives and manufacturers who dont want liability problems are reluctant to explore these tubes because of the more dangerous voltages. Quite frankly, this is the reason that I have not, and you have not, put the effort into these whopper triodes. I am not sure I can stand higher voltage shock therapy, though I love the 400-500 Volt treatments.
3. DRIVER CIRCUITS: You definetly need more of everything here and that usually means more complexity, and you know what happens when circuits become more complex. For example this challenge was met by Dennis Had in his high powered 805 amplifier which uses an 845 by using a 300B driving an interstage transformer which drives the grid of an 845 This is the Nobu formula of using, in effect, a small single-ended amplifier as a driver stage. This is also the formula that Gordon Rankin uses in his new high powered amplifier which uses the KR52. You need more higher quality/linear voltage swing/low impedance driver stage to make these big mother tubes jump with life. In Italy many use a 2A3 as a driver tube.
4. EMPIRICISM; Because so much more work and experimentation has been done with the lower voltage tubes we all get the benefit of the world wide accumulated wisdom...like the accumulated wisdom of hotrodding a Chevy motor, and this means these higher power triode circuits do yet have the benefit of this energy.
5. PARALLELING TUBES: A common idea is to use 300Bs in parallel to get twice the power, or to put you into the single 845 power ballpark. This can be a good idea, but if both tubes are not perfectly matched you are going to loose the harmonic whole-sity that is the hallmark of single tube circuits. This is a popular idea in Japan because they love the aroma of 300Bs.
6. THE KR PATHWAY: The new KR tubes may be the most sensible pathway to more single-ended power because Count Kront has designed a new category of high powered directly heated triodes. While I use the KR300BXL to get maximum triode cream at 5 watts, the same tube can be used to get 20 watts out of one tube and many are taking this path....and the voltage is a safe 500 volts.
7. POWER SUPPLIES: Higher powered tubes need much more sophisticated power supplies, and this is especially important because of the lower register abnormalities of all SETs. It is very easy to get an overly bloated low end with higher powered triodes. In the Italian and Japanese DIY magazines you see lots of chokes and gagles of tube rectifiers...if you get my drift?
MULTIPLE SETS of SETS
You quest for power is elevated to the highest possible path when you decide to use a tube crossover and have a dedicated amplifier for each driver. In a two way system, with two 8 watt SET ,you will have an equivalent of twice the horsepower....meaning 30 watts, and better transient response, clarity and much lower distortion because you removed the passive crossover. Two medium quality 8 watt amplifiers and one tube crossover will give you a much higher quality sound than one higher quality 16 watt amplifier, and may be less expensive over all. Sadly Americans arent into this trip yet, because the Mr, Smart Guy can use a 2A3 on his tweeter/midrange and a 300B on his woofers, and take advantage of the maximum triode cream for each.
Because you have read my articles about the Sun amplifier you know I am on the verge of becoming a single-ended heretic, because in its current highly tweaked form this push/pull amplifier has captured my musical imagination in a major way...it is so damn single-ended...but it is more. The key is its simplicity, transformer phase splitter, high quality output transformers, and 300B tubes.
My quest is to get you and American designers to pay more attention to this "push/pull" formula, and there is no one yet exploiting this idea in America, so let me give you my concept:
1. Use KR 300BXL tubes and run them so that they are pumping out 30-40 watts, which is a hugh amount of power
2. Make sure there is a totally independent power supply for the input stage, that is well filtered and regulated
3. Use the KR 10 as a driver tube, and a transformer phase splitter
4. Use a tube rectifier and choke for the plate supply
Now the same basic formula can be applied to the higher power KR tubes, because the key to this formula is the use of directly heated triodes, not pentodes in the output stage.
And yes, these will be expensive amplifiers, but they will also be the most refined push/pull amplifiers you have ever heard, never be obsolete and drive almost all the speakers that are worthwhile using.
PENTODE PUSH/PULL AMPLIFIERS
If America could get over its high horespower amplifier fetish, then the American masters could direct themselves to designing really refined pentode amplifiers...meaning no more than 75 watts. Today there are very high quality pentodes available, and the key to their modern use is to design circuits that dont need all of that bogus feedback, use transformer phase splitters, and much more advanced power supply design.
Less complicated, meaning less output tubes, gets you much closer to the clarity that you expect in single-ended circuits. It is impossible to get lots of tube to be perfectly synchronized as they push and pull, and you can hear that discombobularity, once you have used single-ended triodes as your referen
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