Author Topic: DHT ............LOVE? HATE? MAGIC??  (Read 230 times)

Offline mresseguie

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DHT ............LOVE? HATE? MAGIC??
« on: May 05, 2020, 05:47:01 PM »
Okay, gang.

Absolutely no politics in this thread. I want to learn about DHT. I know this thread is in the amplifier/preamplifer circle/tubes sub-circle, but I don't want to limit discussion to amps and preamps. There are DHT DACs out there, too.

I'm specifically curious to learn about what makes DHT so great. I'm considering upgrading my already impressive SW1X DAC III. One upgrade option is to add DHT. [Don't know how much it would cost yet.] Someone on AC turned me onto a long thread on DIYAudio. I've only just scratched the surface of that thread.

Talk to me. Why are DHT components so sought after?

Michael
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Offline P.I.

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #1 on: May 05, 2020, 07:44:12 PM »
Okay, gang.

Absolutely no politics in this thread. I want to learn about DHT. I know this thread is in the amplifier/preamplifer circle/tubes sub-circle, but I don't want to limit discussion to amps and preamps. There are DHT DACs out there, too.

I'm specifically curious to learn about what makes DHT so great. I'm considering upgrading my already impressive SW1X DAC III. One upgrade option is to add DHT. [Don't know how much it would cost yet.] Someone on AC turned me onto a long thread on DIYAudio. I've only just scratched the surface of that thread.

Talk to me. Why are DHT components so sought after?

Michael
This comes down to my basic tenets of audio.

I’ve always been a less is more guy.  Triodes are pure devices.  You put “X” in and you get “X+” out.  Simple - more voltage out than in.

Any time another aspect, component or device is inserted into the equation they bring non-linearities into play.  Elimination of non-linearities (distortions) gives a clearer picture into the recordings.  Add to this the fact that triode gain stages distortion components (there is always distortion) is predominantly even order - consonant - in characteristic.  I prefer my distortions to be musical and not sound like rocks being slammed together.
"A man with an experience is never at the mercy of a man with an argument." - Hilmar von Campe

Offline Triode Pete

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #2 on: May 06, 2020, 05:53:38 AM »
Okay, gang.

Absolutely no politics in this thread. I want to learn about DHT. I know this thread is in the amplifier/preamplifer circle/tubes sub-circle, but I don't want to limit discussion to amps and preamps. There are DHT DACs out there, too.

I'm specifically curious to learn about what makes DHT so great. I'm considering upgrading my already impressive SW1X DAC III. One upgrade option is to add DHT. [Don't know how much it would cost yet.] Someone on AC turned me onto a long thread on DIYAudio. I've only just scratched the surface of that thread.

Talk to me. Why are DHT components so sought after?

Michael

From my TWL website...

"In 1926, the ‘71A direct-heated power triode was introduced, followed by the ’50 in 1928, the ’45 and PX4 in 1929, the PX25 in 1930, the 2A3 in 1932, the 300A in 1936, and the 300B in 1938. Over 94 years after their introduction, these triodes continue to be the simplest lowest distortion amplifying devices ever made."

Like Dave said (in a nut shell), Simpler is Better... I like the K.I.S.S. principle!

There may be lower distortion devices, but they involve more complexity & perhaps negative feedback to become more linear...

Cheers,
Pete
« Last Edit: May 06, 2020, 07:05:57 AM by Triode Pete »
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Offline S Clark

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #3 on: May 06, 2020, 07:15:37 AM »
I'd never owned a speaker efficient enough to be driven by flea watt amps, but that changed when I picked up a pair of Altec Valencias for peanuts.  So, I'd never thought about a DHT amp before, but I could jump at a kit for the right price. 
“In the end, we will remember not the words of our enemies but the silence of our friends.” Dr. Martin Luther King, Jr.

Offline rollo

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #4 on: May 06, 2020, 08:39:14 AM »
  They have a "Presence" to the reproduced sound that other tubes cannot duplicate. I would vote "Magic"

charles
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Offline P.I.

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #5 on: May 06, 2020, 11:29:49 AM »

DHT tubes indeed are magic, especially used single ended.  They have a linearity that is natural, not beaten into supmission by negative feedback. It is the feedback that is the magic killer. I still have a 572 tube here that I acquired as a spare.  They are now readily available again.  Their scarcity was what prompted me to sell my Cary mono blocks.  They had 20 HUGE watts that had bass response to the earth's core.  I'm saving my $$$ to acquire another pair when I find them.  The Cary SLP50B with the mods I made to it (including using a 6H30 Reflektor Tube) and the 572SE MkII amps was an amazing combination.  This plus the light generated by that 572 was all the light needed for listening at night.

What I really want is a pair of Border Patrol 300B amps... they are stunning!   Too much money for this old man, though  :(
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Offline mresseguie

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #6 on: May 06, 2020, 12:16:09 PM »
Thanks, guys.

Question: In your opinion(s), is it better to have DHT in an amp, a preamp, or DAC?

Secondary question: Since I already have tube amp and pre that I love, doesn’t make most sense in my situation to insert DHT into my DAC?

Michael
Daedalus Audio Apollos; Fritz Loudspeakers LS/5-R
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dB Audio Labs Tranquility SE DAC w/Jupiter Caps
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Offline P.I.

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #7 on: May 06, 2020, 09:29:15 PM »
Thanks, guys.

Question: In your opinion(s), is it better to have DHT in an amp, a preamp, or DAC?

Secondary question: Since I already have tube amp and pre that I love, doesn’t make most sense in my situation to insert DHT into my DAC?

Michael
Michael,

Let logic prevail.  You have a pre and amp that float your boat, right?  Then a DAC with DHT  I/V conversion or output buffer is where I would suggest that you look.  There is that “righteous soulfulness” that goes along with DHT SET. 

This from a dude that was stupid enough to sell his  :roll: ...
"A man with an experience is never at the mercy of a man with an argument." - Hilmar von Campe

Offline rollo

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #8 on: May 07, 2020, 08:04:50 AM »
Michael, you have two choices IMO. A Amp or DAC.


charles
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Offline steve

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Re: DHT ............LOVE? HATE? MAGIC??
« Reply #9 on: May 07, 2020, 10:18:06 PM »
I pondered whether to post any information, either pro or negative, but I have some information that virtually no one ever posts, or has seen, so I have decided to post it here. Some time ago, I also posted at some info on AC. Anyway, here goes.

I must add that some two decades ago, there was a fierce marketing campaign on to push SET amps, especially using DHT tubes (along with profits). All kinds of superlatives, specs etc given to DHT amps.
Virtually no one had/has the equipment to separate truth from fiction.

There are hardly any accurate/natural sounding amps available of any type. The main difference claimed
is the "midrange magic". This is partly due because:

1. The DHT distortion claim is 2nd harmonic in nature. This sounds good except:
 
     A. the distortion spec is virtually no better than any other tube. Below I compare a 300b to my
         SET using IDHT, and my PP amps. In both cases, my amps have much much lower distortion.

     B. that there are 3rd, 5th, and 7th order products produced, just like other 3/2 power tubes. Check bottom
         of post to view Eimac data.

2. The midrange "magic" is also due to weak frequency extremes (parafeed operation may help the bass). The weak frequency extremes are due to low transconductance input/driver tubes, poor quality, small size of coupling capacitors, and DC current through the output transformer (OPT) reducing the primary inductance and increasing the distortion (See RCA Radiotron Designers Handbook.)

The result is the mid-range dominates.

3. The SET amplifier is basically a simple build, regardless of tubes used. However, there are hidden faults
inherent in the design.

     A. The damping factor varies from near infinite (right at clipping), to the min RP/OPT, for any type SET amp.
The reason is that the plate resistance of the tube varies with signal level, regardless of tube type,
DHT or IDHT. PP basically does not have this problem and yet can also be designed for true accuracy/naturalness
claimed by SET fans, and with more power output. The only drawback, the design is more complicated requiring more expertise.

     B. The intermodulation distortion (IMD) is very generally 3 times that of the harmonic distortion (HD) figure. Thus for 5% HD, the IMD is some 15%. For 10% HD, the IMD is some 30%.

4. The lowest distortion tube ever produced is the new JJ E88cc/6dj8, JJ 12at7, 12ax7 line of tubes, and
by a wide margin. We are talking some 1/9th or less distortion, or -18db or less than any 6sn7 or other
tube. A tube with that low of distortion is difficult to work with though.

As mentioned above, below is the distortion products (.pdf) of a typical 3/2 power tube, either DHT or IDHT. The distortion characteristics shown are vs signal drive. Notice 3rd, 5th, 7th harmonics shown. The distortion harmonics vary with amount of signal level at the grid. It also means that at certain signal points, a particular harmonic might be suppressed, or exaggerated.

Below is distortion data of 300b vs power output vs RL.

Just the 300b tube, 4% harmonic distortion (HD) at 6.5 watts output. (see graph below)

My KT88 SET entire amp measured ~2% at 7 watts. So I have to question the low distortion claims of 300bs.

My 20 watt triode push pull (PP) amp produces 0,05% at 1 Watt and 2% at 20 watts (with no global negative feedback of course). At 7 watts the distortion is a few tenths of one percent.

If we discuss intermodulation distortion (IMD); IMD is the sum and difference frequencies produced between two or more musical signals. These sum and difference frequencies are generally not part of live music. Generally speaking, IMD is ~ 3 times that of HD figures.

My KT88 amp IMD is ~6% at 7 watts output.
My PP 20 watt amp has 0,15% at one watt output, and ~6% at 20 watts.
Just the 300b tube has 12% IMD at 6.5 watts.


Another aspect we need to consider is the combination of input/driver/output tubes in an amp.

300b needs up to 200 volts p-p drive signal for full output.
 
KT88 needs 100 volts p-p.
 
6sn7 types have limited gain, so two stages higher distortion to obtain the 200 volts p-p. Older tube
types have poorer high frequency response than new. However, many newer tubes are not that good to begin with.

The saving grace might be that the frequency response of older, low gain tubes starts dropping 1/3 the frequency vs a good high transconductance tube. 12AT7, X7 types are much much worse.

5. Distortions combine to create new orders. For instance, 2 stage amp, 2nd harmonic from driver tube combines with the 2nd and 3rd from output tube to create 4th and 6th harmonics. 3rd order combines with 2nd and 3rd to create 6th and 9th harmonics. Notice the 7th harmonic is created in a 3/2 power tube so we can obtain 3rd and 7th for 21st harmonics etc. Now add a third stage to the circuit. (The higher the harmonic/order the more sensitive the ear is.)

6. Lastly, one of the main advantages claimed is intimacy. I have noticed that, close up sound at the speaker, but also virtually no sound stage, so two dimensional. Maybe another has heard sound stage?
That is why I left SETs.

Not to toot my own horn, I have auditioned a "Pro Musica" (Champaign, Illinois) latest upgrade to the
Stereo ST70 amp, and have never heard an SET amp come close to the overall reproduction of that amp. Unfortunately, "Pro Musica" is no longer in business, the one in Chitown is not the same guys.

I will say, though, that vs many many other products out there, a DHT amp beats the crap out of them. But I am not going to spend thousands when I can obtain the best for less. But then I am a designer which gives me a leg up over most folks.

If one finds a Pro Musica, 3rd upgrade ST70 edition, I would highly recommend it with NOS tubes.

Enough of my rant.

steve
« Last Edit: May 26, 2020, 05:53:32 PM by steve »
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