[Pez]

Been looking at a lot of different DHT SET designs and just wanted to get peoples general impressions as to which attributes make someone pick one of these over another. I know power is a big factor, but for now lets stick to sonics.

The tubes I am interested in getting opinions on are:

45

2A3

300B

211

845

No IHT tubes please, but if you have another DHT tube that you think is sonically superior to any of these I am all ears. Probably looking for a tube rectified, 0 feedback, ultra-orthodox type tube amp.

Thanks!

[Tyson]

845's are the best, because all the other numbers are lower.

[bigjppop]

845's are the best, because all the other numbers are lower.

Awesome... that's my kind of reasoning!   

[Niteshade]

Pez, here are some tubes you overlooked:

6N7
6SN7GTB
GM70
572B
813 (Pentode)

All these tubes are power tubes. The first two are indeed power tubes with decent plate dissipation. Parallel them for more power. GM70's, 572's & 813's are great performers and do not have priced based on hype.

[JoshK]

I think this topic is like which is best, tubes or SS?   Which is best, CD or LP?  etc.

The topic is argued to death on SET forums.   There are some generalities or "common wisdom" but I typically find common wisdom to be pretty off.  I think the driver has as much to do with the sound often associated with the output tube than the output tube itself.

Some of the generalities I have heard is that the 45 is ultra pure, precise, open but often a little lean.  It isn't any wonder since it is so lacking in power and bass takes power.  300B is often said to have glorious midrange but the highs and lows are rolled off.  The 300B isn't the easiest tube to drive and most vanilla drivers/topologies are going to stress the driver which would likely make this type of sound. 

The 2A3 is quite popular.  I think it is due to quite a number of reasons.  1) it is readily available.  There are tons of NOS 2A3s still on the market of a variety of makes so you can roll tubes till the cows come home, 2) it is relatively easy to drive, so usual suspect drivers can be employed.  3) it makes some power 3-4 watts, which is more than a host of DHT choices.  4) it has low output impedance so it makes winding an output transformer with wide bandwidth possible, which means its easier to make good OPTs for 2A3 amps, which is a very big part of the SET sound. 

Most 2A3s, not including the original but hard to find RCA harp filament single plate tubes, are essentially 2 45s parralleled inside one bottle.  The "dual plate" 2A3 is this, basically two 45 plates in parrallel.

The 2A3 also has many twin sisters like the 6A3 and the 6B4G.  The 6A3 and the 6B4 use 6.3 volt filaments (like EL34 et al) instead of 2.5V.  The 6B4G uses an octal base instead of the UX4 (4 pin). 

NOS 845s and 211s command insane prices.  New production chinese 845s can be good, but aren't as hardy or said to be quite as good as NOS. 

Both of these big bottles are transmitter tubes with serious plate dissipation capabilities, which also means they are often run at very high voltages which makes manufacturing of the amps both expensive and dangerous.  Of course, they can be run at lower voltages but then they put out power more like the 2A3 and 300B while producing way more heat due to the heavy filament draw. 

845s at high power operating points are very hard to drive due the need for lots of gain at low distortion and ability to deliver some current at the same time to avoid slewing (rolling off of highs).  This is not an easy task and designers spend a lot of time coming up with clever ways to do it.  Single stage 12AX7/6SL7 drivers need not apply.

The 211 makes the demand on the driver a bit less daunting as it has high gain, so it requires a bit less gain from the driver.  However, this comes with a price to pay.  This means more miller capacitance, meaning it is easier to slew if the driver can't deliver some current and second the output impedance is higher which means the output transformer is harder to make well and at this power it is already damn hard.

I believe the design compromises have as much or more to do with the sound of these amps than the tube itself, but I have no proof. 

The 845 is said by some to sound a bit like the 45 (clear, linear, etc) but will big balls.  Of course it puts out way more power so it should have more balls.  The 211 is said to be a little leaner.  I think this is due to the output tranformer difficulties.

Then if you want to get a little bit more obscure you also have the following DHTs.

VT52, 46, 50, PX4, PX25, AD1, RE204, WE 105D, GM70, 75TL, 75TH, 304TL, 801A/10Y, 71A

[Niteshade]

I made an 8 watt 6N7 amplifier and it fits the 45 tube description. It's a prototype and the lean quality can be corrected with better components and a different circuit. Other than that, I love the amps!

So far, I have avoided 300B's. Too expensive for what you get! RF tubes do sound good and I have both 845 and 813 amplifiers. Other, less expensive tubes and designs work just as well if not better.

NOTE: You'll oftentimes get better deals and performance off the mainstream path. Some of it is not hype. It is indeed more expensive to design around RF tubes. That's a fact.

[Quiet Earth]

Great post Josh  I haven't heard most of the tubes that you mentioned, but I totally agree with your point about proper gain staging. Gain and power staging are key in amplifier design.

When you say "readily available" I have to raise a small flag. If readily available means that there are a lot of 'em on e-bay, then that's a "qualified" readily available. The buyer must be ready for a certain amount of trial and error before they receive what they thought they were buying. That's just my experience anyway.

Also, I'm not not sure if 300Bs are the most expensive power tubes. For example, new in box matched JJ's 2A3s and 300Bs cost about the same. I don't really see a bargain when it comes to choosing a power triode.

[JoshK]

Great post Josh  I haven't heard most of the tubes that you mentioned, but I totally agree with your point about proper gain staging. Gain and power staging are key in amplifier design.

When you say "readily available" I have to raise a small flag. If readily available means that there are a lot of 'em on e-bay, then that's a "qualified" readily available. The buyer must be ready for a certain amount of trial and error before they receive what they thought they were buying. That's just my experience anyway.

Also, I'm not not sure if 300Bs are the most expensive power tubes. For example, new in box matched JJ's 2A3s and 300Bs cost about the same. I don't really see a bargain when it comes to choosing a power triode.

The JJ 2a3 is a 300B with a 2.5V filament.  If you operate a 300B at 2A3 op. points you get less distortion as a result. 

[Pez]

Damn Josh, thanks for the extensive info. Not at all what I expected but certainly puts into perspective how complicated a decision like this can become!

[lonewolfny42]

845's are the best, because all the other numbers are lower.

 

+1 .....and they sound good as well... 

[JoshK]

Essentially SET amp design is all about tradeoffs.  There is a power vs. low voltage (usually mutuall exclusive), ease to drive versus ease to make good output transformer for, weight versus compromised filtering, etc, etc.

SET designs are strictly class A, so there aren't ways to cheat by allowing crossover into class B. You get out roughly 1/5-1/4 what you put in (assuming half way decent SE efficiency). 

[Niteshade]

Do people consider using expensive tubes that are even more expensive to design & build around a reasonable thing to do, on average?  Saying something is expensive is a relative term, I realize that- but not when looking at the ratio of wattage to dollars to performance.

[JoshK]

Do people consider using expensive tubes that are even more expensive to design & build around a reasonable thing to do, on average?  Saying something is expensive is a relative term, I realize that- but not when looking at the ratio of wattage to dollars to performance.

But hi-fi isn't about good economics, its about getting the best sound at all costs.  Purist SET lovers, rarely are willing to accept IDHT, strapped pentodes or parrallel output tubes as a solution, considering all of those solutions as an inferior design.

People spend so much money on this hobby.  Just look at the number of >$1,000 power cords, and then consider that $300/pr for new production 300B tubes isn't that big of a deal.  KR, EML and new production WE 300Bs at $700-1000/pr seem to sell very well. 

[Niteshade]

I see your point, but their assumption that expensive triodes are the only conveyance for high quality sound is 100% wrong. They do possess a specific flavor of sound, but I would never, ever call it superior. It is simply different. I like the richness of 813's (pentodes) & 845's myself!

How many of you have heard an 813 amp? It's a large RF pentode, about the size of an 845 physically. I cannot tell much of a difference between the two. The specific qualities of warmth and richness are abundant in both tube types. I find them superior to 300B's so far. I find they both have a smooth (a little overly smooth) upper frequency response.

But hi-fi isn't about good economics, its about getting the best sound at all costs.  Purist SET lovers, rarely are willing to accept IDHT, strapped pentodes or parrallel output tubes as a solution, considering all of those solutions as an inferior design.

People spend so much money on this hobby.  Just look at the number of >$1,000 power cords, and then consider that $300/pr for new production 300B tubes isn't that big of a deal.  KR, EML and new production WE 300Bs at $700-1000/pr seem to sell very well.

[JoshK]

I see your point, but their assumption that expensive triodes are the only conveyance for high quality sound is 100% wrong. They do possess a specific flavor of sound, but I would never, ever call it superior. It is simply different. I like the richness of 813's (pentodes) & 845's myself!

I am just describing what I see as audiophile popular "wisdom".  There is also a very elitist aspect to this.  If it is common and easy to come by it makes it a lot less exclusive and more pedestrian, so the snobs will shun it, consciencely or not.

I have a small collection of 813 and GM70s myself.  They can operate near similar op points, so a little jiggering of the socket should allow to compare.

[Quiet Earth]

Niteshade,
Couple of friendly points, to help your manufacturing curiosity. Just my two cents.......

#1. As a consumer, I don't want to buy an amp that uses uncommon tubes or tubes that are only available from ebay. I want to be able to buy new replacement tubes from a retailer that stands behind their sale. Sure, I can buy NOS tubes on the bay if I want to, but not because I have to. This may not seem reasonable to the DoItYourself hobbyest or Factory Direct seller, but as a typical consumer I think it's fair.

#2. Expensive Power Triodes. I keep hearing that my single ended 9 watt amp uses expensive triodes (300B). Can you please tell me what an inexpensivetriode is? One that I can buy brand new, with warranty, from a reliable tube vendor?

Or does expensive mean that I should switch to single ended EL34s because they are so much cheaper than 300Bs. Then I defer to point number 3.

#3. I like to make my final choice of which finished product sounds the best and which one is worth spending my money on based mostly on what I hear. This is in conjunction with learning the academics on forums like this one. It also means going to a bricks and mortar store and auditioning the damn thing for myself. This proves to be the best way for me to buy gear without having to resell it on Audiogon. I realize that this is a very old school train of thought, but if I were manufacturing a product that I really believed in, I would start building a good relationship with some dealers and do business the old fashioned way. This would also give me tremendous feedback about my product, which would be used to fine tune my business model. Just my two cents in a twenty dollar world. Don't get upset  .

#4. The best sound quality (from a consumer point of view). Based on #3 above, when I hear an amplifier that sounds better than my single ended 300B amp, then I will move on to that, regardless of the topology. I'm willing to change when the evidence is clear.

[Niteshade]

All power triodes are expensive relative to most audio pentodes.

I don't have a problem with folks who like triodes. I happen to like them too. I'm pointing out the very real fact that there are alternatives that can sound as good or better that are more cost effective.  I can say this based on another fact: Not all hardware is created equal and assumptions should be thrown out the window.

Brick & Morter stores: I am not going to comment, just set fourth a fact: They add 50% give or take to a product's initial price. The question I will submit: Is it worth it to pay, say $3,000 instead of $2000 for something? I'm not being critical. This is just a question based on a fact.

When a product is on tour, you can try it for a week and then receive a full refund after it's shipped to the next participant or returned. This way people can try products out without a permanent obligation, in their own home.    The best part: If the individual likes what they hear, they get the product free of shipping charges and without the added 50% markup. A win-win situation.

[mgalusha]

Jason, what you really want are some of the KR T1610 power triodes. They can dissipate 150W and have a cool factor off the charts. 'Course they probably cost as much as your car, are likely hard to drive and are just the thing to have with a baby in the house. Just kidding of course but they are some big, bad ass triodes. About the size of a wine bottle they say.

[mgalusha]

On a more serious note, you're welcome to come by and listen to the 211 amps and I'm sure I can get Jerry to bring his 845's down as well. I did have Jim Rebman's little Tektron with 2A3's for a week to give it a checkup and I liked it as well though it really needed more power to work well with the Abbeys.

The Cyber 211's will make right at 16W into 8R before visibly clipping on the scope, the 845's will manage 24W. As Josh mentioned, both of these are tough to drive though there are some heroic designs to manage this. I have been gathering the parts to build the tube labs 845SE, which uses a power MOSFET to provide enough current to drive the 845 into A2 and it will grunt out about 40W, provide of course one has sufficient power supplies. Almost forgot, I have a "Mr. Liang" 845 amp as well. It's going to be the doner for my 845SE but it's still stock, or nearly so. It uses a 300B to drive the 845's but only manages about 12W before it clips.

Mike

[Steve]

845s at high power operating points are very hard to drive due the need for lots of gain at low distortion and ability to deliver some current at the same time to avoid slewing (rolling off of highs).  This is not an easy task and designers spend a lot of time coming up with clever ways to do it.  Single stage 12AX7/6SL7 drivers need not apply.

Hi Josh,

I am glad you brought this information forward. For the general public, I have a white paper that discusses the distortion problems of drivers/input stages and how it affects higher order harmonics at the output, as well as other causes of distortions. It is important to keep the input/driver stages harmonic distortions low as those harmonic distortion products combine with the output tube's distortions to produce higher order harmonics (let alone intermodulation distortion products).

http://www.sasaudiolabs.com/theory9a.htm

The higher the drive necessary (higher the negative bias voltage is), the harder it is to minimize both harmonic and intermodulation (IM) distortions. A rough general rule is that IM distortion is 3.2 times the harmonic distortion, regardless of what type triode is used. It is very important to design an SET amp very carefully for superior results.

Cheers.