GoodSoundClub - Romy the Cat's Audio Site - Some very good points... and... possibly more logical reasoning?

02-06-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	152
Post ID:	9655
Reply to:	9651

The YO186’s sockets and prices

KM,

Yes, it turned out that the B4/B5 sockets are not a problem at all. I do not like the original sockets with springy contacts and I like the contemporary sockets that hold the pins with full micro-tubes.

Regarding the YO186’s price - this is difficult. There is no price form them as there is no market for them, they just not available for sale. There are some prices perhaps in Russia but considering that they have just a few of them change hands per years then the prices might be whatever asked. The reason why I got them because I came across a party of 10 tubes. I would not buy 2 or 4 of YO186 as I would never find more if I like then and need them more but I figured out the 10 of them might be a life-long supply. I will not incriminate myself by saying how much I paid for them – it was more then might be considered sane. I just will say that it was comparable to the prices of the period 2A3, but still lover then it would be for a brand new RE-604.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-07-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	154
Post ID:	9662
Reply to:	9661

My attitude toward tube rectification.

It is only if you chose to employ tube rectification. Many people claim that tube rectification affects sound greatly in this or that way and they are right, it does. However, it does only because the circuit is designed to be affected by rectification. Let see what we have in case of tube rectification. Uselessly after the rectifier we have a small cap to ground then in best case a choke and another small cap. In better case we have another few CL or RC chains. The rectifiers can’t handle fast inrush of current to charge big caps. To put time delays is expensive, so most of the tube amps end up with 20-100uF anode cap. The ripples looks like more or less killed, and AC coming from tube look like has some path to ground. However, the capacitance of the last cap before anode is small and cap does not act as brick wall, shunting all AC right the way to ground, letting the AC voltage from plate to “see” choke and to see the rectifier tube. Sure, in this case the sonic characteristics of choke and rectifier maters.

Look what I do. I use SS rectification and invariably input choke filter with additional RC chain. The key in here is to use the last cap of a large value that would decouple the PS from AC voltage. This way rectification is less irrelevant and I did a bunch of the tests to confirm it. In fact I found that tube rectification had lighter lower frequency harmonics that I did not like.

I can give you an interesting test to look into it yourself. Take you normal tube rectified SET mono-blocks (A and B). Drive A amp normally but B amp connect in a kinky way. You need to power the driver stage off the B amp from the last cap of the A amp’s power supply. Then feed the A amp with signal but listen not the A amp but the result of penetration of AC voltage unto the B amp. Diving the last cap on the A amp down you will make the AC voltage from plate of A amp to find ground deeper into A amp’s choke and rectifier. The further ground is the better sound you will hear via the B amp. Your objective shall be to have the worst sound from B amps, or in the best case absolute silence from it. In this case the A amp will be indifferent to anything behind the last cap. I made those experiments and … I do not listen the sound of rectifiers. I do not say that it is imposable to make good sounding amp with PS elements being “in AC path”. I just try do not do it…

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-08-2009

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floobydust

currently roaming the US
Posts 62
Joined on 01-19-2009

Post #:	155
Post ID:	9665
Reply to:	9662

Tu-be or not Tu-be, seems Tu-be the question.

I've used both tube and solid-state rectification over the years and much is well documented for power supplies, i.e., old ARRL manuals, Tube manuals, etc.. In most cases small value filter caps were shown, as you really couldn't get much in larger values beyond 40-50uf with high voltage ratings and they were quite large... and electrolytic. As you start to examine older electrolytic capacitors they were somewhat odd and putting too much capacitance on the rectifier tube would result in some (internal) fireworks display. So recommended cap values were kept small.

Enter the age of solid-state rectifiers, high PIV and current ratings and many (me included) went in this direction. In my view, the real advantage was the introduction of better quality and high volumetric efficiency capacitors like Sprague DX and Mallory CGS computer-grade units. These made it possible to provide large reservoir low-impedance supplies. If you use good quality (electrolytic) caps, then you shouldn't need to parallel additional small-value caps to compensate for alleged poor performance. Multiple paralleled caps of disparate types typically result is some form of "tank circuit". If you hear audible differences by adding a small value cap in parallel with your large value filter caps, I would suspect you have the wrong caps in the first place or you're hearing the result "tank circuit" interactions.

In my recent Class-A SET designs, I've returned to a vacuum-tube rectifier with a classic pi-filter. Reasoning behind this is three-fold: 1st- with a small 2-4 watt Class-A SE mono amplifier, you do not have large changing current demands on the supply, 2nd- there are now some really excellent large value/high voltage film capacitors available and 3rd- A properly chosen rectifier tube will provide adequate delay to allow the filament in a DHT to heat up and stabilize before the B+ ramps up. As previously noted, designing such a supply can be a challenge, but if managed properly, you shouldn't hear any sonic change by swapping (good quality) rectifier tubes. If you do, I would suspect that you either have (or had) a bad rectifier and/or the power supply design does not isolate the voltage ripple properly and/or output impedance (relative to load) is too high making it sensitive to component changes.

My SET 45 amp uses power supply iron (power transformer and filter choke) that is rated 300% higher than what the circuit requires, this results in cool running, good regulation and a clean/quiet output. The rectifier tube is also rated for a typical operating current 300% more than what the circuit draws. Of course the proof is in the operation. Using a 5V4G rectifier, a 15 Henry choke and a pair of 40uF/630V Axon film caps and less than 40ma total current draw, scoping the B+ output at normal operating conditions reveals virtually no ripple and/or voltage fluctuation. One side note.... the initial prototype used a pair of 100uF/450V CGS caps. No issues with the 5V4G but I noticed random voltage spiking on the scope trace... switching to the Axon film caps eliminated this. I suspect the random voltage spiking to be the result of chemical processes within the electrolytic cap unless someone else has a better reason.

Regards, KM

... just because you're paranoid, it doesn't mean they're not after you ...

02-09-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	156
Post ID:	9689
Reply to:	9635

It looks like DHT DSET is shaping up.

This post is a continuation of my late desiccation with Chris from:

http://www.GoodSoundClub.com/TreeItem.aspx?PostID=9641

David Slagle have made the OPT for YO186

http://www.intactaudio.com/forum/viewtopic.php?p=3560

Ideally I would like to try in their 20:1, 25:1 and even 30:1, loading the output tube less and less and to see how S2 driver will behave. David does not do re-mapable secondaryies but he does replaceable coils, so it might be still coming. Still, I think 20:1 might be a good place to start. The inner-stage will be transformer will be 70% nickel, 20% of chocolate, 5% of rose’s smell and 5% of penicillin. Go figure how it all will work together. Theoretically this transformer "as is” would allow to drive any 2A3/45 type of tube in a good “unloaded plate” mode. Let see where this fly will lend. The inner-stage transformer will be here in 2 weeks and then I am planning to start destroying my Sun Audio kit with 6E5P-2A3 and to experiment with my new version of DHT Milq before I apply the changed (if they were worthy) to the 6ch Melquiades DSET.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-12-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	157
Post ID:	9729
Reply to:	9466

The Sylvania 2A3 NOS report

Okay so I got the NOS Sylvania "Spring Top" dual filament 2A3 tubes and have been listening to them for a while, now I am ready to make a report on the tube.

The tube is well built and structurally sound. Tapping gives a very small "tabla" sound dying away quickly, but there is also a moderate amount of persistent jangling, in comparison to the other tubes I have been discussing, but not as much as the Sophia, which went on for minutes. From this I expect the Sylvania to be sort of in the middle of all the tubes, more musical distortion, better presence than other NOS tubes. Yes, this is roughly what I found, in fact.

The frequency extension is limited; not very much in terms of bass response at all, in comparison to the new manufactured tubes. Within the frequency range the timbre produced is correct within the midrange and reasonably close in the higher frequencies, though in the upper range, there is some malcontent. The waveforms are not precisely reproduced, giving a rounding of the attack and a sluggishness in the decay. In this respect it is worse than new manufactured tubes but better than other NOS tubes. There is more harmonic distortion with noticeable congestion and sibilance. It adds warmth to the sound, giving a very slightly romantic feel, much less than other NOS tubes like the mono plates, but the flavor is there nevertheless, although I am splitting hairs.

The differences are very slight and I think would be unimportant for most listeners, considering the huge price difference between the NOS tubes and the new manufactured tubes. IF I had never heard the new tubes from Sophia, Kron, or Emission Labs, there is no question there is a lot to like about the NOS tubes. Compared to the Russian or Chinese tubes, the sound is more balanced, the timbre more correct, the presentation more appropriately relaxed. Of the NOS, I absolutely agree the Sylvania 2A3 is quite nice, giving a more correct, less romantic presentation.

However, there is no comparison to the expensive tubes from Kron, Sophia, and Emission Labs. These are all in a separate category. These produce a very different sound. It is like this: on the old black and white TV sets, there were controls for brightness and contrast. The NOS Sylvania tube has the controls set quite well, but it is a totally different ballgame from a new color TV. Now, some movies, like Citizen Kane, depend on black and white. It would not work in color. Likewise, the NOS tubes present the music in a unique way the new tubes do not.

However, for me, I am focused on the connection to the Sound, and this is something the three new tubes do very well, most of all the Kron, but also the other two. If you have the money to spend on the new tubes and this is your goal with the Sound, there is no question you should do it.

Adrian

02-12-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	158
Post ID:	9730
Reply to:	9729

The Citizen Kane syndrome.

drdna wrote:
However, there is no comparison to the expensive tubes from Kron, Sophia, and Emission Labs. These are all in a separate category. These produce a very different sound. It is like this: on the old black and white TV sets, there were controls for brightness and contrast. The NOS Sylvania tube has the controls set quite well, but it is a totally different ballgame from a new color TV. Now, some movies, like Citizen Kane, depend on black and white. It would not work in color. Likewise, the NOS tubes present the music in a unique way the new tubes do not.

This comment of your about “some movies” makes developed nerviness in me. What in your view in the Kron, Sophia, and Emission tube would not allow them to operate in monochrome setting? Are they so saturated with color that they toss them where they shell not? I do not want to be completely taken away by your association but am a bit concern the you still give some black/white credit to NOS Sylvania. Can you more elaborate on it? Where is from you view is the place where the NOS Sylvania still hold the ground?

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-13-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	159
Post ID:	9731
Reply to:	9730

Sylvania 2A3 in a World without Color

Romy the Cat wrote:
<P>
drdna wrote:
However, there is no comparison to the expensive tubes from Kron, Sophia, and Emission Labs. These are all in a separate category. These produce a very different sound. It is like this: on the old black and white TV sets, there were controls for brightness and contrast. The NOS Sylvania tube has the controls set quite well, but it is a totally different ballgame from a new color TV. Now, some movies, like Citizen Kane, depend on black and white. It would not work in color. Likewise, the NOS tubes present the music in a unique way the new tubes do not.
</P>
<P>This comment of your about “some movies” makes developed nerviness in me.  What in your view in the Kron, Sophia, and Emission tube would not allow them to operate in monochrome setting? Are they so saturated with color that they toss them where they shell not? I do not want to be completely taken away by your association but am a bit concern the you still give some black/white credit to NOS Sylvania. Can you more elaborate on it? Where is from you view is the place where the NOS Sylvania still hold the ground?</P>The Cat

I would not say that the Sylvania tube does anything better than the three new tubes (by Kron, Sophia, & Emission Labs). When I was done with the listening tests, I removed the Sylvania tubes and put them away. When the Kron tubes were re-inserted the Sound returned.

To explain, with a black and white TV, you will never run into problems like "too much green", aspect ratio wrong, HD dithering algorithm not working right. It just doesn't happen. However, you may find a black and white TV that really excels for what it is. All the NOS 2A3 tubes have some distinct limits: they all seem to have no real bass response, and give a slightly warm, slow, mellow presentation. This can be nice if you like that sort of thing. (I mean by comparison the new Chinese tubes sound awkward and harsh.) Within the NOS limits, the Sylvania does very well, but it never goes "outside the box." It just does very little wrong, and in the problems I have heard in NOS tubes, the Sylvania balances them. If you have ever heard NOS 6SN7 tubes, the perfect comparison is the Tung-Sol VT-231 round mica. Can't really complain, it accomplishes the audio checklist, but it lacks the connection to the Sound.

However, the three new tubes (KR, SE, EL) go into a new territory. In my opinion the price difference with the new tubes is justified. Sell all your NOS tubes and buy one pair of new tubes without hesitation.

Adrian

02-13-2009

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floobydust

currently roaming the US
Posts 62
Joined on 01-19-2009

Post #:	160
Post ID:	9736
Reply to:	9731

Are NOS and new manufacture comparing oranges to oranges?

Adrian,

Thanks for a most interesting post. I can't fully respond to this as I don't have the new tube brands you have. I posted earlier regarding my personal findings with the EML 45 solid-plate versus NOS however. Ultimately I found that my Sylvania made 45 NOS tubes to perform better and preferred them, especially in light of the mechanical sensitivity I experienced with the EMLs. The latter will certainly cause audible distortions induced from the sound itself modulating the internals. As a result I found the (known good) NOS 45 to provide a more neutral and accurate sound.

Some of your comments do cause me to wonder about some things... mainly the conditions of your tests. It's unclear (at least to me) what amplifier you are using as a test subject and what are the specifics regarding it. Things like circuit topology, biasing points, loading, driver stage details. In some cases, new amplifiers and/or DIY amplifiers have been customized for a specific tube. As I found previously the EML 45 needs additional bias current to perform it's best when compared to NOS 45 tubes. So if the amplifier used was biased specifically for the Kron 2A3 (just an example) then perhaps the NOS 2A3 was no longer running in an optimal setup. Of course, I'm only guessing here... but did you measure the operating points and performance of each tube in the amplifier or only listening tests? In my humble view, if you don't verify proper operation of each set of tubes, then the overall test is somewhat suspect.

I also have to question if many of the new manufactured tubes with old tube types (ala 45 and 2A3) even qualify as being a "true replacement" or is really a different design with "planned specification adherence" to the original. Case in point, I've read that a certain new 2A3 tube is identical to their 300B tube with a different filament voltage. I've also seen heavily extended ratings for some 2A3 tubes with plate dissipation well beyond 50% of the original. My case (again with the EML 45, as it's the only one I can truly comment on) makes it pretty clear that the new manufactured version is in no way, shape or form a true 45 DHT as there is nothing in common with the original right down to every internal component. Not to mean it's not a good tube, but to point out that is not a true version of the original.

Based on my experience with the EML 45, I would not be inclined to purchase a pair of their 2A3 tubes... but the Kron tube seems intriguing and I may look into their 2A3. In any case, again, thanks for the candid review/comparison. As for the 45... I couldn't possibly agree on selling my NOS versions for a pair of the new manufactured ones... no way!

Regards, KM

... just because you're paranoid, it doesn't mean they're not after you ...

02-13-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	161
Post ID:	9737
Reply to:	9736

That all is incorrect in a way….

KM,

Very good points. There is one more moment that I would like to pay attention. The new prediction tubes are more powerful then vintage tubes. They all claim 1 extra watt because “better materials were used”. So, I wonder, if it would be possible that in some cases Adrian’s old tube run out of power as Adrian did mention bass deficiency. Also, the new tubes might have less grid current and as soon the 2A3 runs out of negative grid voltage and grid current begin to rise then the old tube might need more powerful driver.

So, without a demeaning the results of Adrian’s finding I would propose that his observations are good as they are but if we would demand a definitive comparing then more methodologically kosher environment shell be used. I would say that to be on a save site it need to be sure that both old and new tubes are used in the equal way. I think two measurements are necessary. First one, is to show how a given tube battles A2 class or how linear it is with positive voltage on grid. Let agree the for 3W tube it matters. Second, I would like to make sure that each tube individually set it the right operation point. I would like to drive a full power over the tube and to see that currant and voltage would clip at the same time. Ok, now it the interesting moment – what to do it they are not the same. To change operation point? To change loading? All of it affects Sound it and the question would be: what is the sound of tube vs. what the sound of the given operation?

I have to note that the Adrian’s comment about the saturation of colors most likely are the not the properties of operation but the properties of the tubes themselves. We do not know for how long but it is what it is. Still my general views on audio suggest me that comparing of tube is necessary to do only in context of the whole framework and in context of the specific intentions of reproduction. Let say for instance that Adrian has a park of all drivers out there and he reports that Silvania 2A3 with one specific driver sounds identically to the Emission Labs with another driver under identical clipping and A2 conditions. I think it would be a useful and indicative illustration. Unfortunately not one does it, .... and frankly speaking…. no one need it… the live is too short to waste it to those things…

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-13-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	162
Post ID:	9739
Reply to:	9736

NOS vs new 2A3 tubes

First of all, this not an attack on NOS tubes and it is all meant to be just sort of fun and educational. I happened to have all these 2A3 tubes side by side for comparison, so why not? I also have done the same thing with other tube types like 6SN7 but since nobody on this website uses 6SN7 in a circuit, I do not think it will be interesting to post it.

floobydust wrote:
I can't fully respond to this as I don't have the new tube brands you have. I posted earlier regarding my personal findings with the EML 45 solid-plate versus NOS however. As a result I found the (known good) NOS 45 to provide a more neutral and accurate sound.

Anyway, no response necessary. I am just doing this for fun. Keep in mind also that the NOS Sylvania tubes are very good and to my ears better than many of the new manufactured tubes from Russia, China, etc.

floobydust wrote:
I also have to question if many of the new manufactured tubes with old tube types even qualify as being a "true replacement." Not to mean it's not a good tube, but to point out that is not a true version of the original.

Well, yes, does it really matter, so long as it achieves the goal in the circuit if it is a "true 2A3." I don't see it as a Formula 1 race. However, I get the point, which goes along with my feeling that the Kron tubes and the two mesh plate tubes are sort of revolutionary with distinctly different sound, not characteristic of the limitations of the standard 2A3 tubes. An example: the side mirror was created in racing when a rear view mirror view was obscured by the engine/frame. The car was disqualified that year anyway, but side mirrors are now standard. We should not reject or exclude improvements to design.

floobydust wrote:
Some of your comments do cause me to wonder about some things... mainly the conditions of your tests. It's unclear (at least to me) what amplifier you are using as a test subject and what are the specifics regarding it.

It is the Moondog 2A3 circuit, basically which can be seen at http://home.earthlink.net/~ivol/audio/moondog.htm.

floobydust wrote:
Perhaps the NOS 2A3 was no longer running in an optimal setup. In my humble view, if you don't verify proper operation of each set of tubes, then the overall test is somewhat suspect.

Sure, but on the other hand I would say it is a fair test in that all tubes were run under identical conditions.

floobydust wrote:
Based on my experience with the EML 45, I would not be inclined to purchase a pair of their 2A3 tubes... but the Kron tube seems intriguing and I may look into their 2A3.

The mesh plate tubes are quite different; do not discount them.

Romy the Cat wrote:
So, I wonder, if it would be possible that in some cases Adrian’s old tube run out of power as Adrian did mention bass deficiency. Also, the new tubes might have less grid current and as soon the 2A3 runs out of negative grid voltage and grid current begin to rise then the old tube might need more powerful driver.

So, without a demeaning the results of Adrian’s finding I would propose that his observations are good as they are but if we would demand a definitive comparing then more methodologically kosher environment shell be used. I would say that to be on a save site it need to be sure that both old and new tubes are used in the equal way. I think two measurements are necessary. First one, is to show how a given tube battles A2 class or how linear it is with positive voltage on grid. Let agree the for 3W tube it matters. Second, I would like to make sure that each tube individually set it the right operation point. I would like to drive a full power over the tube and to see that currant and voltage would clip at the same time. Ok, now it the interesting moment – what to do it they are not the same. To change operation point? To change loading? All of it affects Sound it and the question would be: what is the sound of tube vs. what the sound of the given operation?

Again, it is just a my own test in my own circuit with a few listeners. I would say that my impressions of other types of tubes generally coincide with the many stated on various forums, so I do not think my set-up is abnormal in any way; it is a real-life application for 2A3 tubes and I expect any 2A3 I buy to function in it.

I again just mention that the Sylvania 2A3 has a "kind of neutral sound" - not audio neutrality for the Sound as has been discussed here before, but more regular audiophile neutrality, with middle of the road balance and omission of errors. It is not a bad tube, actually a very nice traditional 2A3.

Adrian

02-13-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	163
Post ID:	9741
Reply to:	9739

The identical operation environment?

drdna wrote:
First of all, this not an attack on NOS tubes …

A very strange introduction. Since when people post at this site feel a need to ask apologies for attack or not attack anything? Also, where this phase “attack” ever came from? Adrian I can assure you that people who find useful for them to visit this site, not to say post here, have no personal spiritual investment into any agenda. So, would you attack the NOS tubes or not attack them it recognize as nothing else them your assessment of NOS tubes. If people feel that you “attack” the NOS tubes then the people are idiots and who care what they feel. I do not know many idiots in audio who feel that expressing a justified criticism is a personal attack. I have seen intense cases when people go to extremes, whoring own wife and losing all dignity and respect to truthfulness/really just because somebody express a skepticism toward to their sound (like that dirt from the PA’s Mill). I true hope that those attitude are not reveling in this site and there is no need to remind that your objectives are not “to attack”.

drdna wrote:
Again, it is just a my own test in my own circuit with a few listeners. I would say that my impressions of other types of tubes generally coincide with the many stated on various forums, so I do not think my set-up is abnormal in any way; it is a real-life application for 2A3 tubes and I expect any 2A3 I buy to function in it.

Well, it is not a conversation about your set-up “being abnormal in any way” but about evolution methods. It you replace your 6SN7 with other vintage then it would be not a big deal and the result will be demonstrate the difference in the tube. Even if you run twice more current over your driver tube it will not affect sound a lot. The output tube and partially in no feedback amp is a different story. Some NOS and the new tubes are so different then need to be used differently in order to have own best respectful applications. I just say the it is very difficult subject and juts puling the tubes in and out is NOT always send the very different tubes in identical operation environment.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-13-2009

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floobydust

currently roaming the US
Posts 62
Joined on 01-19-2009

Post #:	164
Post ID:	9742
Reply to:	9741

Preferred 2A3 operating point

Adrian, Romy, et al,

Okay, I don't take any of it as an attack... so none of that bothers me.... I'm fine with it... again, it's a view on what you heard based on your test scenario, nothing more and I certainly welcome the review. Now that I understand it... here's some of my (personal) viewpoints on this.

The Moondog design goes back a good 10 years now, is a straight-forward design and there's basically nothing wrong with it. If you do some modeling you're running about 15.5 watts of dissipation on the plate and pushing over 4.5 watts output. Running the higher B+ voltage (350 volts) with a 1K cathode bias resistor and the 2.5K load results in higher distortion than the text-book operating point, which is B+ of 300 volts and a 750 ohm cathode biasing resistor and the 2.5K load.

From my findings with the (NOS) 2A3 and higher voltages, going to a higher plate load impedance makes a large difference by lowering distortion. My basic 2A3 SET design uses a 3.5K load with a 866 ohm cathode bias resistor and a 350 volt B+ supply. This was far more optimal and provided much better (clean) low-frequency response and a noted reduction in measured distortion and better wave-form symmetry. I also tested with a 2.5K load and a 1K cathode bias resistor.... so at least with NOS 2A3 tubes, performance suffered.

I have a "gut feel" that the new manufacture 2A3 versions may perform better than the collection of NOS tubes I used for validating my design (literally over 50 of different brands) at the operating points of the Moondog. Again, a gut feel... nothing more. One last point to consider.... I've not seen any specifications for new tubes which state what the interelectrode capacitance values are. As pretty much all of the new tubes are NOT the same materials and/or internal construction, it's unlikely they are the same in these measurements. This could result in an audible difference based on the driver circuit and available slew rate and current flow. If I were to obtain a pair of KR 2A3 tubes (I'm thinking about them... but they are very pricey!) I would certainly go back and optimize the operating points for them. I had to do this for the EML 45 tube and it paid off in better performance (ad more power).

Regards, KM

... just because you're paranoid, it doesn't mean they're not after you ...

02-13-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	165
Post ID:	9743
Reply to:	9742

The sound of the 2A3 however?

floobydust wrote:
Running the higher B+ voltage (350 volts) with a 1K cathode bias resistor and the 2.5K load results in higher distortion than the text-book operating point, which is B+ of 300 volts and a 750 ohm cathode biasing resistor and the 2.5K load. From my findings with the (NOS) 2A3 and higher voltages, going to a higher plate load impedance makes a large difference by lowering distortion. My basic 2A3 SET design uses a 3.5K load with a 866 ohm cathode bias resistor and a 350 volt B+ supply. This was far more optimal and provided much better (clean) low-frequency response and a noted reduction in measured distortion and better wave-form symmetry. I also tested with a 2.5K load and a 1K cathode bias resistor.... so at least with NOS 2A3 tubes, performance suffered.

Perfectly reasonable, however I would be very interested to know the way in which the sound changed with the adjustments, beyond oscilloscope measurements with the different ways you tried it. This would be useful information to me.

Also what is interesting is that the general observations I have had are similar to those of others who have used these tubes in different circuits. That is the sonic differences remain consistent. So I wonder how profound would be the sonic impact of the optimization of the circuit you speak of. No doubt a tube must be operated correctly to do its best, but the question to me is how big is the reward and in what respect it affects the sound.

Adrian

02-14-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	166
Post ID:	9747
Reply to:	9742

Circuit modification for 2A3 optimization

floobydust wrote:
If you do some modeling you're running about 15.5 watts of dissipation on the plate and pushing over 4.5 watts output. Running the higher B+ voltage (350 volts) with a 1K cathode bias resistor and the 2.5K load results in higher distortion than the text-book operating point, which is B+ of 300 volts and a 750 ohm cathode biasing resistor and the 2.5K load. From my findings with the (NOS) 2A3 and higher voltages, going to a higher plate load impedance makes a large difference by lowering distortion. My basic 2A3 SET design uses a 3.5K load with a 866 ohm cathode bias resistor and a 350 volt B+ supply. This was far more optimal and provided much better (clean) low-frequency response and a noted reduction in measured distortion and better wave-form symmetry.

Okay, so do you have some specific suggestions for modification of the exisiting circuit? I am willing to do it and then repeat my comparison tests to see what result the changes will give.

floobydust wrote:
I have a "gut feel" that the new manufacture 2A3 versions may perform better than the collection of NOS tubes I used for validating my design (literally over 50 of different brands) at the operating points of the Moondog.

I would agree. I usually think the NOS tubes are better also. However, the improved design 2A3 are actaully an improvement to my ears. Too bad about the price.

Adrian

02-14-2009

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floobydust

currently roaming the US
Posts 62
Joined on 01-19-2009

Post #:	168
Post ID:	9749
Reply to:	9748

2A3 voltages, loads and realized output power

Adrian, Romy, (Dima),

First, I most certainly agree that the textbook operating point for the 2A3 is not optimal and can be improved on, hence my own design from a few years ago. If you are sticking with a 2.5K load, you will simply not get the most from the 2A3, distortion will be higher and waveform symmetry will suffer. This is validated by hundreds of hours of research/testing which included calculated load lines, software simulations and most importantly, bench time with over 50 different NOS 2A3 tubes using different load impedances, plate voltages and bias currents. Measurements were done using a Fluke digital meter (for DC voltage measurements), Tek 2215A dual-trace scopes, HP 400FL True RMS meters and a 334A Distortion analyzer with a clean sine/square oscillator.

From all of my research on this tube, I feel quite comfortable stating that 3.5K is the optimum load. Going lower increases distortion and going higher results in a loss of power with no tangible benefit. At 275 volts and a 4.1K load (15-watt Pd) you'll be lucky to get much more than 3-watts. You simply don't have the voltage to swing. I prefer ~290 volts on the plate (plate to cathode measurement). I also run the plate dissipation up a bit higher to 17-watts. Note: I don't see this as any sort of risk provided you have adequate ventilation around the tube. What is critical is NOT to exceed the rated cathode current of 60ma, as this will decrease the usable lifespan of the tube.

In my existing (implemented) design, I have a 350-volt plate supply, a 3.5K primary OPT, and an 866 ohm cathode bias resistor (bypassed). Pd is 17-watts, cathode bias current is 58ma and it puts out a solid 4.5-watts with good NOS tubes before any clipping occurs, and the clipping is symmetrical. The performance is also very consistent with the majority of the 2A3 tubes I have. There are of course some NOS tubes which are not so good... I even have two with grid leak problems despite using a 249K grid resistor.

Still, I'd be very interested to hear what Dima finds in his testing.... and of course which tubes he winds up using for his tests.

Regards, KM

... just because you're paranoid, it doesn't mean they're not after you ...

02-14-2009

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drdna
San Francisco, California
Posts 526
Joined on 10-29-2005

Post #:	169
Post ID:	9750
Reply to:	9749

Optimal operation of 2A3: an experiment

floobydust wrote:
[The Moondog amplifier has] a higher B+ voltage (350 volts) with a 1K cathode bias resistor and the 2.5K load.

Romy the Cat wrote:
...the most proper operation of this tube will be at 275V on plate and 4.1K load.

floobydust wrote:
3.5K is the optimum load. I prefer ~290 volts on the plate (plate to cathode measurement). I have a 350-volt plate supply, a 3.5K primary OPT, and an 866 ohm cathode bias resistor (bypassed). Pd is 17-watts, cathode bias current is 58ma and it puts out a solid 4.5-watts.

So it would require a new OPT to be made with around 3.5-4K primary impedance. The power the amplifier puts out is already far too much. I always have the volume dial around 1-2, so this will be okay. I don't have such an OPT on hand so I will need to buy one...

Will that be an adequate test or would you suggest changing the values of R9 and R10 also?

Adrian

02-14-2009

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Paul S
San Diego, California, USA
Posts 2,672
Joined on 10-12-2006

Post #:	170
Post ID:	9751
Reply to:	9749

Tubes, Whole Circuits, Expectations and Sound

It sounds like a lot of the circling has to do with which 2A3 "sounds better", outright. In any case, I'm guessing everyone would agree that it is specious to argue about which 2A3 sounds most like some internally-established aesthetic benchmark for 2A3s. I certainly hope no one cares about that. The idea is to get the "Best Sound", period; right?

The fact is that "new 2A3s" are often thinly-disguised 300Bs, and they can easily up the ante with respect to power, which often gets short shrift from flea-power afficionados. Well, if it's power one wants from a 2A3, then why not start out with a clean-sheet design based on one of the new breed of "2A3s"?

As it happens, I prefer the best part of the "neutral" sound "character" of old, tres-expensive 45s to anything else I've gotten to listen to long enough to establish a sense of its contribution to the sound. Yet, I have never actually owned a 45. The reasons for this are purely practical; basically, it lacks the range and power to drive acceptable speakers well enough to play Music to my satisfaction. The 45 sounds great; but it can't make great Wagner. And as I progressed with the more-powerful 2A3, I wound up with the same problem, even with A-2 via the very-hearty older Sovteks (which the circuit was built around, BTW). I can only guess whether others have FR speakers that are somehow efficient enough to overcome the problems I encountered; but I have my suspicions...

With respect to circuit design, one of the most facinating things I have learned about electronics for hi-fi is that any theoretical solution to a given problem requires an all-inclusive, 4-D, total-system perspective; and still one is apt to wind up scratching one's head at results. From Miller Effect to ESR, on and on, real world circuits are "dynamic" in every sense, and they are in every sense woirthy adversaries, to say the least. For instance, although I have no idea where the actual power goes, I have begun to see a pattern of diminishing net returns with respect to the smaller SETs, to the point where I wonder if their "potential" can ever be practically realized as Music in Full Glory.

Regarding 2A3 selection, my impression here is that we all +/- understand the in's and out's of operating points; but we all have different systems and it sounds like we also have different expectations at this time.

Lastly, the choice of an output tube for MF-only DSET for a single 109 dB horn-loaded compression driver casts an entirely different light on the subject, I think. If there is a real possibility, then this might be close to a case where one need only look at the straightest part of the plate curve of a 2A3 (or 45) and build to that, irrespective of "power". I have had some luck adapting phono stages this way; but so far, no keepers from amongst the small SETs I've played with.

Paul S

02-14-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	171
Post ID:	9752
Reply to:	9750

Gain is not power.

drdna wrote:
So it would require a new OPT to be made with around 3.5-4K primary impedance. The power the amplifier puts out is already far too much. I always have the volume dial around 1-2, so this will be okay. I don't have such an OPT on hand so I will need to buy one...

Adrian, what you report that your amp “puts out already far too much” is gain not power. You have two driver stages each of them 20 times gain, so you have too much gain, not power. BTW, if I were you I would get rid one stage as it is absolutely not necessary in this design. I do not like high-gain 2A3 –who heed high gain if it is not supported by sufficient power? I did have 2 stages, one stage, one parallel 2A3 and one 6E5P (which is 30 times gain with one stage). I do not like too much gain for given power as it driver the power tube deeper to A2 – way would we want it? BTW, when you go from the “standard” 2.5K load to 4.2K you will lose some gain.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-14-2009

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	174
Post ID:	9755
Reply to:	9754

6C33/2A3 DSET?

drdna wrote:
How about using the 6C33C for the low midrange-woofer, the 2A3 for the upper midrange, and the 45 for the tweeter? I suspect if each circuit can be optimized, that they can do their best within each frequency range.

Hm…. I do not think that it makes sense in your particular playback. You use Edgar’s refrigerator subs that use own LF SS amps (that use EQ of I am not mistaken), so you do not use the full advantage of SET LF sound. To construct 6C33C DSET juts for sake of upperbass driver doss not sound reasonable to me. Now, if you intend to drive you subs and upperbass from 6C33 then it is while another story. Then you might have 2-way DSET with let say 500-600Hz break and it might be an interesting solution. The key would be to found out what kind loading the refrigerator subs would demand and if the 6C33 will have enough power to drive the LF. It would be also nice if the upperbass would be OK with the same loading as bass would demand. Then you can go line level-crossover for MF (big advantage) and do not case about the power from your 2A3. Theoretically it possible to make a situation when the 6C33 and 2A3 would be driver from the same PS but it would be too difficult…

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

02-14-2009

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floobydust

currently roaming the US
Posts 62
Joined on 01-19-2009

Post #:	175
Post ID:	9756
Reply to:	9752

SET usable power and making the most of it

Well... tis for all reading/following this thread.

As Romy pointed out, having high gain is not the same as power. And as Adrian hinted at... the overall system paradigm is important. If you're only barely cracking the volume control on your amplifier or preamplifier then it should be obvious that you have more gain than you need. Personally I don't put volume controls on power amplifiers... I prefer ONE point of control, not multiple... but to each his/her own.

If you're designing and building your own equipment then managing the system as a whole becomes less of an issue. If you're picking piece parts (either built, kit or implementing somebody else's design) then you need to manage the various gain of each component and determine how to best integrate them into a system. As far as the gain in the amplifier goes, it's a moot point IF you manage the overall system gain properly. I've done two SET designs over the past few years... and they are quite different on gain, yet have very similar specifications. There are both technical and financial reasons for each design but both have been optimized for performance, not gain. Also, both take into account the OPT winding/phase and result in a non-inverting design.

A brief word on power.... the 45 triode in a proper design will deliver a solid 2- to 2.5-watts and can be flat from 20Hz to 50KHz (or more) depending on the design, components and how it's actually built. A 2A3 triode will deliver up to 4.5 watts in the same application... please note that this is ONLY a 3dB change (double the power). As such, it's not really surprising that you (Adrian) realized little benefit from the 2A3 over the 45... you didn't gain very much (power). Having speakers which have higher sensitivity is a real requirement for using low power amplifiers. And even then, the last 1 to 2 octaves will require some additional help for anything beyond moderate listening levels. There's no free lunch to acheiving SPL levels.... it's a match between the sensitivity of the speakers and the available output power, i.e., no magic involved.

If you plan on using 2- to 5-watt SET amplifiers, you need to mate them with speakers of adequate sensitivity AND which will mate well with a low powered SET, of which most (if not all) have no negative feedback and have low damping factor. This places a much greater demand on the type of speaker that will perform well with the amplifier. Personally, I find the sonic neutrality and open soundstage of a properly designed SET to be the dominant factor that makes me want to use one. The (technical) reasons are beyond the scope of this post however. The down side is two-fold: 1- The electrical and mechanical parameters of the speaker (impedance curve, self damping, moving mass, etc.) can wreak havoc with any SET design. 2- Low frequency performance will be limited regardless... as you walk down the scale of organ pipes you simply need more power and larger drivers to deliver those low pedal notes. Getting the last couple of octaves will require additional support and you're not going to manage it with low powered SETs.

As for modifying your Moondog amplifiers, I would recommend against it. While you can effectively reduce the overall distortion and gain a bit of additional power, it's not worth gutting the amplifier and start swapping out expensive parts. If you're not happy with the amount of power now, NO change will fix it as you simply can't gain enough power to deliver Wagner.... also what speakers are you driving with the MDs? You would likely be better off with a different (SET) amplifier which has enough power to meet your needs.

Regards, KM

... just because you're paranoid, it doesn't mean they're not after you ...

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