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Melquiades Amplifier
Topic: DHT driver & input

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Posted by guy sergeant on 02-01-2007
Hi Romy,

I currently use a 3 stage transformer coupled amp with 112's, 71a's (as drivers) and your favourite 300B output valves:-) I'm not sure whether I'd go back to a capacitor coupled amp. I just acquired some Tango NC20 IT's to replace the NC14's that currently load the 71's and will be interested to see if they are as good as they are reputed to be.

It does seem that with DHT's how the filament supply is arranged has a huge effect on the resulting sound. All 6 of these valves are powered by Guido Tent's filament supply boards.

Posted by Romy the Cat on 02-01-2007

Splitting the Lamm ML3 thread:

There are some people who worship direct-heated tubes and attribute to them some ventures (like absent of higher harmonics and a special micro-fineness). There are other people who see in that micro-fineness an excessive granularity – I tend to agree, but my bias primary based upon ignorance…

I do not know exactly, as I hardly heard any SETs that I like generally and particularly a properly used SET. I personally had no seriously-made DHT in my room. Frankly speaking considering what I’m getting out of Super Milq I see no motivation to peruse anything else for my system. However, I would like to keep open mind I do not mind to educate myself about the capacity of the direct heated tubes.

Dima is considering 6E5P-2A3 for himself… but I would like to see a DHT amp use direct heated driver not only DHT output state. Above I said about seriously-made DHT, what did I mean? Most of the people when they build of design amplifiers they juts orange parts together in according of the rules of circuit operation and by mingling with those parts characteristic they try to get out of their amplifier different “Surrogate Sonic Effects”:

I find those “accidentals” amps that produce the “Effects” are boring. By demanding SERIOUSNESS in amp making I mean the creator of amplifier had very sell defend sonic statements. They he made his amplifier to express Sounds in accordance to the statements, in accordance to the ways in which the creator’ consciousness advised him. After all, an amplifier should be rendering humans intentions but not vise-versa…

So, If someone know any seriously-made, two-stages, probably mid-frequency-centric amp with direct heated driver AND direct heated output stage, preferably made around tubes of 30s-40s then I would go to listen or might borrow it. In exchange, to keep the person intrigued, I might lend to the DHT owner my full-range Melquiades….

The Cat

Posted by Romy the Cat on 02-01-2007

 guy sergeant wrote:
It does seem that with DHT's how the filament supply is arranged has a huge effect on the resulting sound.

Could you elaborate on  that “huge effect on the resulting sound”? What does it means and how did you come to the observation about those meanings?

Romy the caT

Posted by guy sergeant on 02-01-2007
I made a simple SE amplifier using the 6B4G for a friend. Initially, it was ac heated and sounded fluid & lively with a very agreeable gentle quality particularly with strings and woodwind. But, however I arranged the ac supply & hum bucking methods I couldn't get it sufficiently quiet and did feel that there was some strange upperbass imprecision on almost all of the music I tried. I wasn't sure whether this aspect was due to the output transformers or some by product of the remaining hum.

I started by supplying DC via a simple bridge circuit using fast recovery diodes and capacitance which significantly reduced the noise but which also flattened the pallete of colours the amplifier seemed to have at its disposal. Where it had been eager and colourful it became much less engaging. I experimented with various regulators but still felt that this 'washed out' character persisted. It may or may not be because of the fact that the passive components used in heating the cathode are in the signal path.

I read about the Tentlabs boards and liked the idea of using a high impedance supply which the signal might not 'see' When I fitted them the life, colour and spirit I had enjoyed with the ac heating returned (but without the hum) The output transformers, in this application, were fine.

I'd been meaning to try an all DHT amplifier for a while but had put it off because I hadn't been sure how to make it quiet without compromising what it might do well. For me, these boards work. There are other people in the UK thinking along similar lines (but different approach) to Tentlabs, and I've just received some 7.5v boards to use in a 10Y linestage I've been working on. It will be interesting to see if their solution has the same effect.

Posted by Romy the Cat on 02-01-2007

Welll, you still did not express yourself what are the sonic verdure of DHT from your point of view. You are not obligated I juts proposed you to do it if you feel that have any observations on the subject.

 guy sergeant wrote:
I started by supplying DC via a simple bridge circuit using fast recovery diodes and capacitance which significantly reduced the noise but which also flattened the pallete of colours the amplifier seemed to have at its disposal. Where it had been eager and colourful it became much less engaging. I experimented with various regulators but still felt that this 'washed out' character persisted. It may or may not be because of the fact that the passive components used in heating the cathode are in the signal path.

I personally very much NOT in a position to express an expert or reference opinion about electronics but I have my own undeniable experience that in my mind (and for me only) overrides anything that others say. I experimented with the very same issues you described during the times when I built my 7788-7721 phonocorrector and where I used DC on filaments. I made-many power suppliers for filaments and spend quite a time to listening them.

Tube rectification was the best form a perspective of colors but I never was able to get necessary bass and necessary “rhythm” form tube rectification. I was trying 3-4 different rectifiers and they were all the same, thought there was some difference between them.

The SS diodes driving caps very good bass but the devises that those power supplies drive practically unlistenable tonally. At low current they do sound fine but at higher currents for whatever reason this setting is absolutely disastrous. I found a compromise by lowering the first cap after the bridge with increase of current (of course there is a resistor between the firs and second cap).  The ultra fast but soft switching diodes are better diodes but in this application they do not sound good as well. In order to get any more or less civilized sound at 1A-2A I was forced to drop the first resistor to nF level.

The salvation come when I put a ultra fast but soft switching diodes with input choke. It was like an instant bliss- it had a full bass, full “rhythm” and dynamic but no deliration effects. Eventually I learned that the firs cap after indictor should be small and the first LC chain should form some kind of mimic of a reversed Bessel filter.  Sure the choke should have the necessary minimum inductance to the given current but it very easy to get. Interestingly that this first LC does not necessary kills a lot of ripples, in fact it will be a lot of ripples after it. However, it is ironic but ripples actually do not affect tone. I was driving a lot of equipment with juts a simple LC filter (with very small cap) and I loved how it sounded. Sure it has nose but even there thought the noise it was clearly auditable that it was very problem-free supply from a perspective of musicality. So, I personally do not recognize the input LC chain as a “filter” – it hardly filters anything but rather my “default entry point” form power supply to the rest of the circuit. (in case on constant current of course) From here everything is very simple: one more RC chain with the cap as big as your finance, space, ego or stupidity allows you.

This is what I learned worked for me and since I ma very restricted in my electronic diversification I use the same pattern in PS everywhere. If I make a PS for DHT it would unquestionably go for fast dies with LCRC, probably for a fully balanced LCRC with the last cap of enormous values. What until you guys see the PS for the upcoming Zaratustra II amps – it will be cartoonish…. But still all around the very same idea…

The caT

Posted by guy sergeant on 02-01-2007
What do you mean by 'sonic verdure'? Do you mean virtues?

If so I would say that they typically offer a lighter, unfettered presentation of timbre & dynamic range across the full frequency range provided that the HT and LT supplies allow them to. This has been most noticeable with the linestage project where the 10Y sounds boundless.

I really don't feel that the kind of low impedance power supply that you are describing (particularly if achieved through using large final smoothing caps) will give a good result with DHT's but please feel free to try it. I would contend that the nature and design of a filament supply to use with indirectly heated triodes is very, very different to that required of DHT's. Your LCRC supply will put that large final cap right in the signal path, you won't like the results and may again dimiss DHT's as the misguided fetish of the audio morons! Ah well...

Posted by Romy the Cat on 02-01-2007

 guy sergeant wrote:
If so I would say that they typically offer a lighter, unfettered presentation of timbre & dynamic range across the full frequency range provided that the HT and LT supplies allow them to. This has been most noticeable with the linestage project where the 10Y sounds boundless.

Hm, “lighter”? May I ask you to elaborate more on it? Also, you  do not milliamps anduse juts one SE DHT  amps and drive with it your full range speaker, right?

 guy sergeant wrote:
I would contend that the nature and design of a filament supply to use with indirectly heated triodes is very, very different to that required of DHT's.

Perhaps, I do not know. I never tried to impose any power supplies to any DHT.

The caT

Posted by guy sergeant on 02-01-2007
By 'lighter' I mean that the DHT amplifying stage subjectively has less inertia and is able to change direction more quickly. I suppose nimble might be a better word.

At the moment I usually do use the amplifier 'full range'. (My speakers will not go anywhere near as low as yours) although I have used a cap coupled 845 PP amp for the LF occasionally. To be honest the transformer coupled amplifier is so much better at low frequencies I prefer to use this amplifier on its own. I've yet to try your DSET approach although it does seem a sensible idea. I'd like perhaps to improve the speakers first.

Do read the Tentlabs technical notes on why they think a high impedance DHT supply is preferable. It is explained well enough there. My experience confirms for me the validity of their ideas.

Posted by Romy the Cat on 02-01-2007

Thanks, Guy, for your explanations. Still those “have less inertia and are able to change direction more quickly” I feel has more to do with out intellectual visualization of  how DHT work. I do not think that inertia would be correct concept and heaters do not change the evaporation rate dynamically form cathode. For whatever reason you do not talk about Sound in context of this kind of technical subject. Well, it is fine… You are perfectly with your constitutional rights….

Thanks also for pointing out the Tentlabs flosks. I juts read it. I do not know if what they suggest makes sense. I did not play with DHTs and I have no leverage to judge them.  In IDHT Melquiades I use all possible methods to drive the power supply  impedance as low as possible, who know it migh be with DT it is different…... Perhaps the Tentlabs guys are fine but the comments in their “reviewers” sound absolutely idiotic, not to say self contradicting. People praise the batteries powers supplies and then say that high impedance PS are the best equivalent of batteries…. because of the high impedance. Am I missing anything?  Also, it looks hat they do not use chokes, not to mention many other things that do use…. Anyhow while I read at that site I was not impressed … not to mention that a companies whose site’s have a pop-up pages with ads selling Vaigra and OME software are probably worth attention. Very sad…

Surely it is not my objective in this thread to discover how to heat a DHT. I kind of more was looking for a DHT inspiration. I would like to come across an DHT that would make me to wonder about its sound. So far whatever I head DH sounded more like bad amplifiers…. I do not think that it was because the DH tubes but it eliminated an ability to talk/think further…

It would be interested to have the same tube in DHT and IDHT interpretation and to listen it. I head that 2A3 were made as IDHT (dual) - I wonder if someone one them. Anyhow, I will keep my mind open and perhaps someone would impress me with DHT. Some folks told the foresails about the A1 triodes but looking at what else they those peoples did it more impact me with apologetic feelings then with desire to demonstrate any attention to their foresails …

Anyhow, if some one would bring in my room your serious and full of objections SET (driver AND output should be DHT) then it might be educational…. perhaps for both of us…..

The CaT

Posted by guy sergeant on 02-01-2007
The references to inertia and lightness are not to do with how a DHT works electrically but to do with how sounds reproduced by them 'can' be ie without smearing or overhang. Its a characteristic I hear in live unamplified music and one that is endearing to me. I may be wrong to presume that it can be captured by the recording process but I don't think so.

I don't really have a yardstick for indirectly heated triode power amps. All of the ones I usually hear are godawful OTL designs although as I said before, I did once hear a very pleasant 6336 based amplifier. I've heard various 6C33 based amplifiers at shows but have never found them particularly interesting but then shows aren't the best places to form conclusive opinions. I've heard plenty of poor systems using DHT's at shows too.

With regard to the Tentlabs website, I don't get any pop-ups from it and I pay little attention to what reviewers say. We've discussed this before, reviews & magazines are infotainment and shouldn't be irritating or be taken seriously. You have to try things that seem interesting yourself, not rely on the hearsay of someone with entirely different priorities & questionable (to you) needs. The filament supplies looked like a sensible solution to an awkward problem, I tried them & they worked for me.

Your power supply design approach seems a little dogmatic to me (and won't work in this application in my view) however if it works for you, stick with it. I'm sure there are many people in the US who use all DHT power amplifiers and one or two of them might even be persuaded to submit them for your appraisal. If they do, ask them how they have implemented the filament supplies.

Posted by Romy the Cat on 02-01-2007

Yes, it was kind of interesting. The Tentlabs site does not have anymore those popups (and my machines are environmentally clean). I was so surprised when I sow it that I even went to their web site from my “absolutely clean “server that never ever goes Internet. Anyhow it is not so relevant

What is really interesting if does exist any sonic difference between DHT and IDHT. There is difference between different tubes and between different productions. Would this difference between different tubes more visible then the difference between DHT and IDHT construction? I really do not know. The engineers suggest about some essential advantage of one of other construction but it says a little to me about Sound. I as well have seen and heard plenty of crappy sounding DHT, frankly speaking in most of the cases I head poor sound and I did nit even care to learn what tubes were used. I generally have tendency to express interest only if the result was worthy and I do not accumulate needless audio knowledge.

It would be fun to see some kind of DHT devotee who knows what he does and who can demonstrate the boundary of DHT application. There are a lot of people who make noise about the subject but I never was exposed to anything convincing.  If I have some semi-local serious guy with noble DHT objectives than I might supply him with some interesting tubes. Approximately 8 years ago I bought in German, practically for nothing, a collection of 50-60 tubes; mostly pulls form German radios of 30s. I found it recently in my storage in and I think it might be used somehow. I do not need any amplifiers for myself but if someone is capable and serious about their objective then I would furnish the person with some interesting tubes. As the payback would like be able to learn with results. I know… it is all utopia but if I do not make somebody do the things then I know that I will not be doing it myself....

The Cat

Posted by guy sergeant on 02-02-2007
The 112's on my amplifier were made in 1926. I think they sound good but I actually chose them because I wanted low gain. Regardless of that there is a certain different pleasure to be gained from playing modern recordings using tubes made over 80 years ago. If anyone then thought about it at all, I suspected that they might have expected us to move on from that techology by now. I suppose I could switch to a TriPath or B & O Icepower based digital amp but I'm not sure its progress.

With regard to my earlier posts I was trying to describe sound. Making references to specific musical pieces isn't necessarily helpful to those people who don't have the same pressing, in the same condition, of the same piece of music, played back on the same turntable through the same phono stage etc. Its like me trying to describe the sound of my mother's voice to you. I could but you'd need to hear it to be able to recognise her.

Posted by Romy the Cat on 02-03-2007

If you look among the links of my site then you would see the Netherland's Rob who is deep into the direct heating.

It would be fun to have someone of his level of craziness to demonstrate what direct heating could offer, if any. Some of the things (not all of them) that Rog says at his sute I do appreciate…

The Cat

Posted by aaverhoeff on 03-04-2007
Hello guy sergeant,

I am interested in your experience with the NC14.
Could I send you some questions as a private mail (pm)?

My email is:
(replace _@_ by @)

Best, Arjen.

Posted by be on 03-04-2007
DHT amps can sound good or maybe charming is the right word, but I believe it is due to an error related to the concept of oops described elsewhere on this site.
This is the result of the filaments resonating and contributing with a sense of life and sparkle in the midrange and treble.
You can identify the sound quite easily by knocking on the tube when not playing, the sound you hear will be there in a subtle way, always! Making the music interesting and kind of stimulating for most people.
I built an enormeous 300B amp once and tried a lot of 300B tubes and they all had the same trait but tuned a bit differently.
It is also possible to elicit the voice of the tube by playing certain tunes, here strongly plucked electric guitars are well suited, and then stop the cd in the mibble of the sound, the tube will continue it for a while!
I tried to suspend the tube and dampen it, but it did not seem to help much, so the effect is posibly also due to electrostatic forces internaly.
All other DHTs I heard had the same problem or bonus.
I must add that I dont know if transmiting type of tubes also suffer from this problem, they operate the filaments on a much higher temperature, probably making them softer and less prone to resonate?

Posted by Romy the Cat on 03-04-2007

Well, I least of what “be” proposed is true then it opens up a whole new perspective of thinking.

So, toward this end, since in DHT the filaments are cathodes we could intentionally stress the filaments and by doing it what could inflict sound. Sure it would wary with the way how filaments hanged and particularly since they are heated equally across the whole length, but still…

In context of what “be” suggested it might be understood why some people claim that DHT sound better when filament run by AC voltage. Those people go onto a huge length of experiments and complicity to fight with hum, and perhaps the never defeat it but they believe that “with AC it sound better”. Who knows, perhaps some residual ripples of the 50-60Hs AC do shake the heaters in “positive manner”.

Posted by Paul S on 03-04-2007

No question in my mind that the tubes themselves contribute to the sound we get from tube-based systems.  Funny how I go to such lengths to get "quiet" tubes and use dampers even as I realize that even the quietest tubes are doing their bit to/for the end product.

But surely this tube noise is a matter of degree?  For instance, I once owned the original Music Reference RM-9, which could use EL-34 variants, KT-88 variants or 6550 variants.  Not only were there plenty of differences between the tube "families", but there were also similarities between members of the same "family" that did not seem to be "electrical" so much as "mechanical".  Germane to this discussion, I found the very popular KT-88s to be flat-out too noisy, although other listeners "preferred" the "richer and more immediate/lively" sound.  Likewise with AC powered filaments in some set-ups, where the noise just over rode the other pleasant "effects" for me.  Shades of the "lively" TT set-up... 

Back to the "oops" theory, I suppose, along with all the other "problems" we encounter.  How can we use them to our advantage...

Best regards,
Paul S

Posted by Romy the Cat on 09-23-2007

 Merlin wrote:
Directly heated triodes …. It has fully regulated power supplies and absolutely zero AC filament hum.

That bothers me tremendously is the half-ass approach of high-end products and the fact that for exuberant amount of money, that looks like should assure ambitions solutions and objective methods, the high-end companies still do not go all the way into what is possible of at least available for a premium high-end pay.

For instance everyone knows that DHT sound way more interesting if the filaments are AC driven. To drive them AC requires quite expensive super-precisely symmetric in capacitance and impedance domain transformers. So, Lamm made his ML3 SET with direct-heated GM70 but the amp has use DC in filaments. Sure, it makes the amp “secure” regarding the filament noise but… can something bold and ambitions implementation-wise could be asked form an amp with $125K price tag? If not to demand from those products the “high-end implementations” then from which products it should be asked?

The caT

Posted by Romy the Cat on 11-20-2008

This subject does not bother me too aggressively as I recognize absolutely no sonic demands or listening temptations to change anything in my playback. However, there is a theoretical and conceptual curiosity on my part and I would like to learn what a good direct-heated triode would do in regard to my single 6E6P stage driving MF channel.

I would like to have a good 1W-5W direct-heated SET that was educated to sound right by its owner and to connect it to MF channel of Macondo (15R), I would like to see what it might lead. So, if any of you New Englanders have a good sounding direct-heated SET then feel free to contact me and perhaps we can do a listening session together with your SET and my Macodno’s MF channel. From my side, as the reimbursement for your efforts dragging you amp in my place, I might promise you an educational experience about sound that you most like will not get otherwise.

Rgs, Romy the Cat

Posted by gordan on 01-28-2009
guy, i noticed you've mentioned a DHT 10Y linestage.

i'm wondering what are your thoughts if there is a relatively easily obtainable (in say lifetime quantitiesSmile) DHT (or triode stripped DHP or DH tetrode a la 307A or 807) capable of driving 801A safely into A2 class, interstaged or direct coupled?

i agree with your findings re tent labs DC filaments supply - i have a rather similar thing in my current 10Y SET amps and they do the job correctly on all the 3 stages the amp utilizes.

the reason i'm mentioning 10Y/801A family is that they are still affordable on a silly tube market - you can buy a lifetime supply for a price of a RCA 2A3 NOS pair, plus they IMHO sound better - less prejudiced towards a romantic SET sound we all know (and some try to avoid).

best wishes

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