floobydust wrote:

The main component that limits low-frequency response in any SET is the OPT. For these initial designs, I used the smallest Hashimoto SE OPTs... their H-203S for the 2A3 and their H-507S for the 45 which are rated at 7-watts at 50Hz. Despite their small size they are excellent in quality, both mechanical construction, shielding and sound quality. Tailoring the low-frequency response for any amplifier should be a design factor so you don't over-run the OPT. Such is the case in my design for these. I purposely wanted to roll them off on the low end so you don't have issues with core saturation and/or field collapse within reasonable listening levels.

Yes, I know but I do not particularly care about it as the DSET concept absolutely eliminate all those frustrations with OPT.

floobydust wrote:

Some thoughts on direct-coupling.... for all of the pluses people rave about regarding sonics and such and the removal of the alleged "evil" signal coupling capacitor there are also some negative points which you have hinted at. First, DC coupling does present some additional challenges in the design and maintaining proper DC biasing of the cascaded stages. In many cases, additional circuitry and components are used to compensate for this, many with adjustable resistances to lock it into spec. So that raises one initial question... does the addition of several resistance components where they are of different construction (wire-wound pots, cermet-film pots, wirewound resistors, metal-film, etc.) and/or regulator circuits to maintain DC biasing compensate for the removal of one single coupling capacitor? Which is worse, the cause or the cure? Second, as you noted there is something different in the sound at times. One possible cause is the fact that ANY DC offset and/or low-frequency underlying signal (like record warp) can push the circuit out of it's linear operating region causing high distortions at these extremes and also push the OPT into core saturation and field collapse. This is yet another reason to tailor the low-frequency response of low output amplifiers so they are not pushed out of their linear operating region from signal anomalies.

Valid points, we just discussed with Dima exactly the same, he does not feel comfortable with the direct-coupling, thought I feel that higher frequency the channel operated in the more benefits the direct-coupling has.

floobydust wrote:

Multiple stages versus one. Well, again, a choice that has to be made somwhere in the signal chain from start to finish. Let's start at the output stage... using my little design above, and the 45 triode. In the operating point I use, grid bias is approximately -60volts. Simple math shows that you need to be able to drive the grid at +/- 60 volts or 120 volts peak-to-peak for maximum power without driving the tube into A2 on positive swings or cutoff on negative swings. Due to the multiplying effect of input capacitance, you also need a suitable driver for the output stage. If you go thru the required math and use 20KHz and 60 volts swing you can calculate the required slew rate and minimum driver current to ensure you drive the grid properly... there's no free lunch here. The signal level and drive current must be met or you won't have a clean output stage. In a single stage design, you are completely reliant on the driving source. How many preamps can provide 120 volts peak-to-peak under these conditions? In such a design, the overall sound quality now becomes completely reliant to the what's driving it. Granted, if you design the entire system and take all of these points into consideration for design and implementation than you can manage it. If you plan on using other components... you've lost control.

An interning point. “The signal level and driving current must be met”, I was under impression that we meet the criteria of driving voltage not driving current. I thought that the driving current is necessary juts to push the tube capacitance, which is extremely low in the tubes I use, and other then that the driving current is just the way to load the interconnect before the amp. You feel that driving current play more roles in my situation? Do not forget that I use the single stage amp with 4.5V on grid, so the operation sits deep in A1 with no greet contra-currents in presence (in theory)

floobydust wrote:

As for the input/driver stage I eventually settled on, it has some excellent operating attributes. First, the driving stage (one triode of the 5814A) has ~2.8ma of current and can easily drive 150 volts peak-to-peak cleanly into the grid, meaning it can drive the 45 or 2A3 fully and at wide bandwidth as the response is flat past 40KHz. Yes, you use more drive currrent, but it is somewhat akin to killing a fly... you can use a fly-swatter or a bazooka... end result is still the same... dead fly. You can also look at it's square-wave response and note that it's crisp and clean which supports my calculations on drive current versus required slew rate and voltage swing. The input stage is the other half of the 5814A. The output of this stage is DC coupled to the driver... but, the operating points of each stage are selected to ensure it does not push the driver out of it's linear region. The input stage is biased at ~1.2ma of current and can handle a input voltage of 8 volts peak-to-peak without being driven into A2 or cutoff. Of course, this would result in pushing the driver stage well beyond it's maximum output level, but the design goal is to ensure the input stage has no possibility of being driven out of it's linear region or placing an odd load on whatever drives it, as class A2 would result is increasing current demands from the input.

Hm, interesting, I never seen/heard seen/heard seen/heard this 5814A. BTW, if you have any curiosity then you might try my driver.

http://audiodiy.hangszoro.net/viewtopic.php?p=27004&sid=e009865a60357dfd6f073a61a8872467

Put is at 200V with plate resistor no less then 15K and drive though it is 15-30mA..

floobydust wrote:

Another part of the design is the input bypass capacitor being chosen for a specific roll-off point, again to help reduce large low-frequency input offsets like record warp or rumble. The driver stage bypass capacitor is actually calculated for 1Hz or less as I don't want it adding anything like phase shift but simply following it's input signal. And lastly, the coupling capacitor to the output stage (it's the only one in the design) is also chosen for a specific roll-off point. In all, there are 3 time constants and they are not stacked but each is calculated for a predictable response on low-frequency. The end result was as required, 1dB down at 25Hz, which is 1-octave below the spec'd power level of the OPT.

Good point. The concept is totally irrelevant in DSET application buy still valid generally. Still it is a big question what shell die first – the filter or the OPT from the bottom. I you looked my straggling I had with in past with implementation of MF coupling capacitor as a high filter then you would know what I mean. What whatever reason the inner stage coupling capacitor is not always work good as a bandwidth limiting devise.

floobydust wrote:

So, what am I driving with these little guys... it varies. I do have quite a few speakers at home. I have Quad ESL-63 US Monitors ,but they are far too low on sensitivty for any appreciable SPLs.... but they are gems in their own right with enough power. For single drivers I have a pair of Fostex F120A in 10-liter enclosures I built which are also on the low side, but a few dB more sensitive than the Quads. However, the Feastrex D5nf setup in solid red oak BVR enclosures does have sensitiviy around 95dB. The amplifiers are okay provided you don't push too loud. Granted, having 100dB+ speakers would be a huge plus, but I can monitor output levels with a Mytek DDD-603 and ensure the amps can never be driven into clipping (with digitial sources only). They get loud enough for some very critical listening but of course not loud enough for a symphonic orchestra level. I'm not entirely done on speaker choices yet, but have additional higher powered SETs on the design board. Overall I would certainly recommend the smaller 2-watt 45 amp for driving a high-sensitivity tweeter in a multi-amp system. It's overall linearity is excellent.

Ok, I got the message. Still, as I understand that you are not in over 100dB would? The over 100dB environment in my view set another set of rules. It is not necessary that it would reverse what you say but it kind of different. It would be very interning to hear your thought after you play with well over 100dB sensitivity and it has a different impact to the view what amp shell do. I think instead of having a higher powered SET on the design board you might fish something like JBL 2440 from the ebay pond and see what happen next…

floobydust wrote:

Some very good points here... if I downloaded the correct schematic from your site for the 6-channel Melq amp (also has the term DSET in the title) then you have created a 6-channel SET amp with built-in crossover points. Your first comment makes sense but only for the SET stages that clip the low frequency response out. The full-range and low frequency SET sections are still succeptable to saturation and field collapse.

Yes, but the entire concept of DSET (or Dedicated SET) is disregard the min inductance always to have another channel as soon he saturation of OPT core might be an issue. I mean in DSET would the channel is designed for HF response only. The LF left over is handled by the LF DSET that is made by totally different rule of the SET game. BTW, to understand the Milq properly you might get the full-range Milq – it more illustrative wjat the amps is all about.

http://www.romythecat.com/PDF/Melquiades_SET.pdf

floobydust wrote:

Driving current is still a concern with any tube. You can use some basic formulas to calculate required slew rate versus bandwidth. Your input tube is biased around 4V per the schematic referenced above. My post was specific to the output tube being the 45 or 2A3. The same would apply, but of course the figure would be much lower due to the low voltage swing and whatever the total input capacitance of the stage is. Of course, this is fairly insignificant compared to the input cable capacitance. Looking at the 6C33 output tube, it's quite significant.... for sake of argument…

It is not for sake of argument. The 6C33 is VERY capacitive tube and it is now so simple to drive it. The DHT tubes from this respect are much mach easier and friendlier load.

floobydust wrote:

The 5814A is a ruggedized and improved version of the 12AU7. It has a beefier heater, tighter specs and generally a more robust mechanical structure, i.e., thicker mica supports and in many cases a 3rd top mica disc to enhance rigidity. Beyond this, you design with it like any 12AU7. A very good tube in general. Unfortunately I don't have Russian bottles in my collection... perhaps I should give the 6E5P a try... thanks for the recommendation.

There is a lot of data at this site about 6E5P. It is up to 40mA small 9 pin tube with gain of 30 and 4V on grid. Do you know any other driver that can with one stage to swing 120V at 30mA. It also has some interesting sonic qualities

http://www.romythecat.com/Forums/ShowPost.aspx?PostID=4805

There are tones of them on eBay for $2 each.

floobydust wrote:

On a side note, looking at the specs for the 6C33, I can't help but think that this tube might have had the western 6336 as a model.... maybe, maybe not. The 6336 is designed in a similar way and can actually replace up to 3 6080 paralleled tubes. Another beefy guy with two independant triode sections.

Nope, the 6C33 was one of the very few pure Russian designs, not stolen from West

http://www.romythecat.com/Forums/ShowPost.aspx?PostID=6140

floobydust wrote:

I think I'll agree less on this point... or perhaps we're defining things differently. My point is to limit low frequency to the output stage so you don't have issues of saturation or field collapse, not using it as part of a crossover turning point. In any case, using it a crossover turning point, it's only 6dB/octave and you'll probably want it steeper than that for your MF crossover.

Acalsy I do not know at this point how I will end up for my MF crossover. If I do for DHT and two stages then I would need to reevaluate where I would put the crossover. I might keep it as it is now or might be the coupling cap will work out for me this time. Another option is to put a between the 6E5P and DHT tube a fast inner-stage transformer with around 1H-2H inductance and very limited turns. If I kill all LF before the driver state (as I do now with me RL filter) then I have no capacitance signal path that might be a good way to go (let discard the caps in PS). The point is that with no inductance, very low power and with a fast core the fast inner-stage transformer might have negligible phase problems up to 100K-200K and it might be a good coupling solution.

BTW, do anybody know any indirect heated triode, perhaps larger then 9 pin that I might still employ as the one-stage amp. It would need to have 40-50 times gain at 1K on plate (and proportionally changed), more then 3-4V on grid, work at sub 400V and have final power at least of a couple watts.

floobydust wrote:

I do agree that the internal structure makes a big difference... but, if the tube specs properly and has adequate immunity to mechanical induced interference, then you should not be able to discern any major difference in sound quality, at least not in well made NOS tubes as the industry had the same technology, materials and processes.

floobydust wrote:

Finally, here's the Sylvania 2A3 with the coil spring supports

Very good, floobydust. They are exactly my thoughts about the “period tubes” as well. In addition to that I think that factor that call “Holly Ignorance” did take place with some vintage tubes. They might not have too high demands for the quality of the tubes 60 years back but they have not yet developed bad technological habits back them. It is very similar to making speakers drivers – in past they did not have high demands to quality but they did not have back then the nowadays idiotic ideas how sound might be taken out of loudspeaker by barbaric methods.

Saying that I have to note that that idea of contemporary production by sensible and knowledgeable people of some vintage tubes do look attractive and the Chechslovakians are a good illustration. The concern that I have is that they might replicate and I am sure improve the contraction. However, I do not think that the today tubes makers might do anything with materials. It is highly possible that all materials sources by all manufactures from the same “generic” suppliers – considering the quality of today tubes production no one would cook metals and coatings specifically for tubes. Well, how different would it be from many other fields?

floobydust wrote:

I don't really know anything about the YO185 but would like to see some info if available.

http://www.romythecat.com/GetPost.aspx?PostID=9344

http://www.romythecat.com/GetPost.aspx?PostID=9407

floobydust wrote:

The 10Y was obsolete long ago and the preferred replacement was the 801. While they are similar they are not identical. There are two significant factors that differentiate these from the 45/2A3 variants: 1- They use a thoriated filament/cathode which requires 7.5V. 2- They require a fairly high load impedance (around 7K) and higher plate voltage (around 600V). The down side is also two-fold, higher impedance OPTs are more difficult to make and keep an extended high-frequency response. The filament/cathode design will require a DC supply to keep the hum out. You won't gain any additional output power over the 2A3... about 4-watts max. It will cost more to implement and it's doubtful if you'll get any (audible) improvement over a 2A3.

Hm…  I do not know. I have some sources that I respect who in fact very much encouraged me to go for those thoriated tungsten cathode tubes with very high impedance in plate just because strictly considerations. I less care about the high-frequency response as in my care it will be DSET for 1kHz and up (3200Hz electrically) and therefore the transformer shell not care any inductance. If I go for LF cut off let say 400Hz then it will be possible to use reasonably-minimum amount of widening and HF would not be a big deal. The only thing that holds me is that many of 10Y/VT-25 out there are dead or “wrong version”. I did explore the subject. With 2A3/45 it is more attractive as there are so much more options…….

floobydust wrote:

Finally, I'm not sure where your preceived need of four transformers comes from. I have 45 and 2A3 designs which are flat out to 45KHz at full power with low distortion and the only transformer in the signal path is the OPT.

When I said four transformers I meant that I can see 4 type of the tubes. The 2A3 with 700-80R on plate, YO186 with 1200R on plate, the 45 with 1800R on plate and 10Y with 5K on plate. Hey are requires different transformers.  I do not like taps. I like to have transformer with remapable sections. The 2A3, 45 and YO186 still might be possible to care with one transformer; the 10Y would need a very different beast. Also, I have a filing this time to try something different. I might go with DHT for a slower core OPT but to load anodes more idle – I have a feeling that it might bring me where I would like to be. I am thinking about 4.5K-5K for 2A3 – I mean a lot of impedance, as much as my S2 will be able to handle. I even will to give up a bit speed of my code for trying it…. In my single-stage IDHT amp I have no gain to afore this luxury.

floobydust wrote:

What is/was your thoughts on circuitry?

I invasion absolutely nothing fancy. It might be the very same Milq’s driver stage:

http://www.romythecat.com/PDF/Melquiades_SET.pdf

with only differences that as the output tube will be cathode-based DHT. I still debate if to couple it with good quality cap of transformer of 1H inductance. Bothe ways have attractive sides. Anyhow, I begin to sound like Lynn Olson with his inexhaustible BS-talk about his bogus loudspeaker project…

floobydust wrote:

Okay, I think I understand.... and thanks for the link on the YO-186... if I can ever locate some of these I'll be sure to grab some (hmmm, a trip to Russia perhaps). As tubes get very hot internally, there were some procedures for trying to eliminate the possibility of "out gasing" from the tube elements, if they were exposed to internal heat levels beyond their ratings. Transmitting tubes were a good example as many of these had cherry red to orange anodes for CCS operation. Even the high powered VR pass tubes (6336 and 6528) had anode materials and processes to ensure "out gasing" would not be a problem when deployed in high-current applications. It's not very clear how much of this exists today with some of the new manufactured tubes.

This is one of many subjects that so much attracted by in YO186. It reported that tungsten cathodes have no such a problem (or less) but the oxide cathodes with their higher efficiency have a tendency to gas the tube. When the electrons are boiling on the cathodes it reportedly some kind of gas get created that in a long run screw the tube and the can’t be properly be absorbed by other gas-handling methods. To minimize this effect the pre-fabricated cathodes before they placed into the tubes exposed to overburning. The over burning  reportedly is some kind of sophisticated  ceremony where cathode is heated to very high temperature, much-much higher then it even will see in regular life and then submerges in some kind of cold chemical broth.  It is reportedly a sophisticated and expensive ceremony that was done in past and allegedly discarded by today makers of the tubes. So, according to my Russian sources the YO-186 was exposed for overburning three times (!!!) before the cathode was accepted for this tube. I do not want to create a myth about it but if it was true them it very much goes along with the vision that in past people did not try to save on the things that that are important.  I do not know if all of it true but allegedly the YO186 was one of the very few tubes that was exposed to triple overburning.  Perhaps the facts like this explains why some of the older tubes run for 50 years and still “measured as new” (even I personally do not support this notion)

Floobydust,

I have a question to ask. Those dam Ruskies when they did the YO186 then made it to have an absolutely idiotic pin layout. The layout is very simile to 2A3 but one of the pins a few mm away, far enough for me to consider that it would  not be save to bend the pins. So, what I heard is that in 30-40 Germans made the similar pins and I wonder if any tubes sockets for them are available? I told that there is a Germany aftermarket company that make those add sockets very recently. So, since you are in Germany, or any other Germans – did anybody see the “faulty” not-fitting 2A3 tube sockets? It is not imposable to accommodate some other solution to YO186 but I would prefer to buy off the shelf socket and do not be bothered with it.