If you want to try 'em for yourself, and are concerned with the twice line frequency modulation by AC filament heating, run two valves in parallel with their filament connections opposing. The real challenge with DHTs is getting enough isolation from AC power line garbage, while still making the "cathode" unipotential to signal. Lots of folks have given up and gone to DC heating. But never say die!
All good fortune,
Chris
All good fortune,
Chris
could be many reasons, personal taste, 45 clipping at volume, etc. there is a huge difference in output power between the amps.
in my system, all my friends and family prefer the SET. i could not find a single person prefering the PP EL84 amp. could be many reasons, such as cosmetics or something.
Was the PP EL84 run in Triode class A with ZNFB, otherwise the comparison is not fair. This is the problem with comparing totally different topologies - people rarely build the PP amps to the same standards as the SET amp and then wonder why they sound different.
Shoog
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I also had this experience before, SE tube amp had rich 2nd harmonic, the EL34PP I heard had very fast ,detail sound which different than other PP amp I heard was the same with rich second harmonic.
Hi!
With all plate curve measurements I did, DHTs have been more linear than IDHTs. Especially in comparison to triode strapped pentodes. There had been some experiments done by S. Bench, comparing IDHTs to DHTs and DHTs with oxide and thoriated tungsten filaments. He measureed the change of mu with signal ampltitude. In this test the DHTs had mroe constant mu and among DHTs those with thoriated tungsten filaments had been better
Best regards
Thomas
With all plate curve measurements I did, DHTs have been more linear than IDHTs. Especially in comparison to triode strapped pentodes. There had been some experiments done by S. Bench, comparing IDHTs to DHTs and DHTs with oxide and thoriated tungsten filaments. He measureed the change of mu with signal ampltitude. In this test the DHTs had mroe constant mu and among DHTs those with thoriated tungsten filaments had been better
Best regards
Thomas
i find sets too whimpy for my tastes....the speaker we used was a modified Sony 4 inch FR in a transmission line box......we played Joe Morello's take 5 at volume and one guy came up to me and asked me, where did you put your subwoofer? he was flabbergasted to find out that all we had was a 4incher.......
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I also had this experience before, SE tube amp had rich 2nd harmonic, the EL34PP I heard had very fast ,detail sound which different than other PP amp I heard was the same with rich second harmonic.
with a Broskie CCDA line preamp, the EL34 pp amp sounded better than the 45 set with plenty of volume to boot....
ultralinear pp shuguang EL34 shuguang tube amp.....with global negative feedback......i do not know what the standards for SET amps are, but i do know what i heard and i liked it.....
Data and procedures are generally only given for tubes with specified low microphonics. It's sorely lacking for others. As far as I'm aware, there is no one universal standard.
edit: Here's an example of one where the procedure is specified and data are given:
http://tubedata.milbert.com/sheets/138/6/6111WA.pdf
Here's an example where the claim is made, but with zero supporting data:
http://tubedata.milbert.com/sheets/079/5/5879.pdf
No, reversing the filament connection does not reverse the second-order distortion. Think about it! To reverse the second-order you would need one filament to have quadrature AC supply.Chris Hornbeck said:
I have always assumed that people like DHTs because they are unusual and big and expensive. They seem to be preferred by the sort of people who proudly display their valve amp, as though it were an art object. Any increase in linearity (if it indeed exists) is due to their low gain caused by wide element spacings, not the direct heating. This just puts more pressure on the driver stage. It is conceivable that some people prefer them because the net result is more distortion.
Somehow I have never heard of anyone making a ZNFB (better way to abbreviate that, tnx) amp with pentodes (or beam power tubes). Wonder why?
Generally speaking, perhaps the biggest advantage (despite all other potential disadvantages) is that the harmonic spectrum *appears* to have less "hash" in the highs, and things like the human voice tends (again a rather broad generalization) or should I say *often* sounds more natural and less mechanical or electronic.
Even harmonics or not, less higher order harmonics or not, that's the general effect of SE DHT amps as heard, compared to PP amps, PP w/NFB, and/or solid state amps.
In my experience the better ones are quite good, rather neutral. There are those that are not quite so good, and less than neutral. But few ever get grainy or harsh, or have hash... some do have HF droop, but not the better ones.
DF96, I think Chris Hornbeck was referring to hum cancellation by using two tubes in parallel, heaters in anti-phase, not second harmonic production.
Personally, I don't care what the amp is made of as long as when I listen to it I don't hear *it* and *it doesn't impose itself* on what is being played...
...oh as far as displaying "art" or "totems"? I see plenty of solid state amps, commercial and otherwise that are impressive, beautiful, and even grotesque (at times) that are/were intended to be seen and are "on display" in salons and homes. Don't think it is limited to just DHTs. And, why not?
_-_-bear
Generally speaking, perhaps the biggest advantage (despite all other potential disadvantages) is that the harmonic spectrum *appears* to have less "hash" in the highs, and things like the human voice tends (again a rather broad generalization) or should I say *often* sounds more natural and less mechanical or electronic.
Even harmonics or not, less higher order harmonics or not, that's the general effect of SE DHT amps as heard, compared to PP amps, PP w/NFB, and/or solid state amps.
In my experience the better ones are quite good, rather neutral. There are those that are not quite so good, and less than neutral. But few ever get grainy or harsh, or have hash... some do have HF droop, but not the better ones.
DF96, I think Chris Hornbeck was referring to hum cancellation by using two tubes in parallel, heaters in anti-phase, not second harmonic production.
Personally, I don't care what the amp is made of as long as when I listen to it I don't hear *it* and *it doesn't impose itself* on what is being played...
...oh as far as displaying "art" or "totems"? I see plenty of solid state amps, commercial and otherwise that are impressive, beautiful, and even grotesque (at times) that are/were intended to be seen and are "on display" in salons and homes. Don't think it is limited to just DHTs. And, why not?
_-_-bear
Im a musician, not a EE, so I can't explain how the characteristics of DHTs operate. But I'm entirely convinced that DHTs sound better than IDHTs on a one to one basis where they are roughly comparable in mu and plate resistance. For that reason I've used nothing else for years. But I'm not just talking of output tubes - the big gain in sound quality is with input tubes like the 10Y, 26, 4P1L (in triode) etc. I use them with DC filaments with Rod Coleman regulators and choke input DC supplies. I also use filament bias on all the stages, including the output stage. That's what my ears tell me.
All the arguments about nostalgia etc. are entertaining, but for me it's simply a question of sound quality. I'll carry on using DHTs until something better comes along. That won't be indirectly heated tubes, it'll be some kind of solid state device.
All the arguments about nostalgia etc. are entertaining, but for me it's simply a question of sound quality. I'll carry on using DHTs until something better comes along. That won't be indirectly heated tubes, it'll be some kind of solid state device.
Maybe a solution to the "AC on the filament causing junk in the audio output" would be to run the filaments at some very ultrasonic frequency (like 100KHz, switching power supplies operate around there). The audio would see artifacts at frequencies around the 100KHz ultrasonic frequency supplied, but those could be easily filtered out.
Just thinking out loud here, maybe there's an obvious flaw here I haven't seen yet...
Just thinking out loud here, maybe there's an obvious flaw here I haven't seen yet...
HF heating would work fine, provided that the HF was clean.
Other things being equal, an IHT would be better than a DHT because its cathode would be a true equipotential plane. It just needs a bit more heater power. AC heating of a DHT will create some hum IM - this could make the sound slightly 'richer'. DC heating of a DHT means increased distortion at low currents because one end of the cathode will cut off first.
Other things being equal, an IHT would be better than a DHT because its cathode would be a true equipotential plane. It just needs a bit more heater power. AC heating of a DHT will create some hum IM - this could make the sound slightly 'richer'. DC heating of a DHT means increased distortion at low currents because one end of the cathode will cut off first.
Thanks. Looks like gathering real data takes some pretty expensive equipment otherwise not seen on the bench. I do remember an informal test of 300Bs where a speaker was aimed at the tubes and feedback was measured but that was a specific comparative test. As far as the pencil eraser test goes, I've found that high transconductance triodes like the 5998 are thumpier than DHTs.
John
I'm with Andy on this one. I've bought, built and modified preamps using the 6SN7, 2C22 and 26 tubes, and the 26 I built is the one that's staying in my system. It just sounds better to me.
By better I don't mean syrupy and distorted, I mean clearer, cleaner and at the same time appropriately warm. It did take me a whole lot of work to get there, though, with mass loaded and rubber mounted sockets on a separate subchassis to deal with microphonics, separate power supply with choke input HT and filament supplies (with Coleman reg boards) to eliminate hum, cascoded CCS plate loading, battery grid bias through an LL1676 input transformer, 80% nickel autoformer outputs/volume controls, etc. but I just love how it sounds.
And having a sound that pleases you is the name of this game, right?
And yes, I do display it as a piece of audio jewelry as well...shoot me for my indiscretions ...Check it out:
By better I don't mean syrupy and distorted, I mean clearer, cleaner and at the same time appropriately warm. It did take me a whole lot of work to get there, though, with mass loaded and rubber mounted sockets on a separate subchassis to deal with microphonics, separate power supply with choke input HT and filament supplies (with Coleman reg boards) to eliminate hum, cascoded CCS plate loading, battery grid bias through an LL1676 input transformer, 80% nickel autoformer outputs/volume controls, etc. but I just love how it sounds.
And having a sound that pleases you is the name of this game, right?
And yes, I do display it as a piece of audio jewelry as well...shoot me for my indiscretions ...Check it out:
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I'm sure that is part of the explanation. My first breadboard 26 hummed audibly and made a clunking noise every time I turned the attenuator due to microphonics. It took a lot of time and effort to get it right, but now it is dead quiet (quieter than my 6SN7 preamp) while being extremely musical.
I wouldn't call IDHTs "lesser". I do however believe from my experience that IF you want to spend the considerable effort, time and money on the surrounding circuitry and chassis, that the 26 sounds better than the 6SN7 or the 2C22 in a preamp.
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