DC is just an unnecessary expense and potential failure point.It maybe necessary in some DHT which were designed for DC heaters - but otherwise it brings no practical benefit.
If i can build an AC heated circuit without heater hum - anyone can and that is the simple concrete reality. It is a bad idea to encourage new builders to use the sticking plaster of DC heaters to cover up the failings of bad circuit layout. In the very rare instance where hum can be traced to the heaters then a DC supply is appropriate - otherwise it is a bad practice which seems to be gaining traction due to threads like this.
Shoog
If i can build an AC heated circuit without heater hum - anyone can and that is the simple concrete reality. It is a bad idea to encourage new builders to use the sticking plaster of DC heaters to cover up the failings of bad circuit layout. In the very rare instance where hum can be traced to the heaters then a DC supply is appropriate - otherwise it is a bad practice which seems to be gaining traction due to threads like this.
Shoog
Let me state that one of the reasons for the discussion on post # 22 and subsequent clarification in post # 119, is the possible magnetization of, either the heaters, or the cathodes, or both, due to use of DC current in heaters.
Note, however, that the electrodes of the valves can be affected by magnetization, but the cause is another, and is not the reason for this thread.
To answer your question, a drawing is worth a thousand words.
Unfortunately the only thing I have to draw is my old DOS program for PCB design, and I confess to pass the required format is not easy.
With a little imagination and the help of the drawings, I think words are unnecessary.
BTW, Q.E.D. is an initialism of the Latin phrase "quod erat demonstrandum", which translates as "which was to be demonstrated"
It's a bit pretentious for an explanation so crude, but it is elegant.😀
Attachments
Unless dealing with very low level signals, it really doesn't matter. Not so sure it matters when discussing low level signals (xcvr front ends).
There is a saying "There is no amplifier, better than its power supply"😉
In the old days, capacitors were costly, especially electrolytics, was common at that time see huge chokes, and huge electrolytic capacitors of... 10 uF.
By then it was common practice to use AC on the heaters, and this habit, passed from generation to generation.
Today, there are other things such as MOSFET transistors, operational amplifiers, Schottky diodes, etc.
It's called "Progress"...
It's been a lot of electrons under the bridge.😀
I was also a newbie once, at that time there was no Internet, only old books, old circuits, and old habits...
I was rescued from my confusion by the Dutch, with its magazine "Elektuur", since then I have no doubts in using DC on the filaments.
I want to remark that this thread is not about a particular assembly, but what happens inside the valves.
The demonstration on post # 98 is not very orthodox, neither elegant, but it could be a useful warning about the use of AC in the filaments.
But as Julius Caesar said when he crossed the electrolytic
Alea iacta est
I'm just a TV repairman, nothing I say could convince you...🙄
But what if a superhero of the forum, use DC on filaments in their amplifiers?
http://www.diyaudio.com/forums/tubes-valves/168994-cc-vs-shunt-filament-supply.html
However, there is the possibility that someone you like listening 50Hz/60Hz, and its harmonics...😀
In the old days, capacitors were costly, especially electrolytics, was common at that time see huge chokes, and huge electrolytic capacitors of... 10 uF.
By then it was common practice to use AC on the heaters, and this habit, passed from generation to generation.
Today, there are other things such as MOSFET transistors, operational amplifiers, Schottky diodes, etc.
It's called "Progress"...
It's been a lot of electrons under the bridge.😀
I was also a newbie once, at that time there was no Internet, only old books, old circuits, and old habits...
I was rescued from my confusion by the Dutch, with its magazine "Elektuur", since then I have no doubts in using DC on the filaments.
I want to remark that this thread is not about a particular assembly, but what happens inside the valves.
The demonstration on post # 98 is not very orthodox, neither elegant, but it could be a useful warning about the use of AC in the filaments.
But as Julius Caesar said when he crossed the electrolytic
Alea iacta est
I'm just a TV repairman, nothing I say could convince you...🙄
But what if a superhero of the forum, use DC on filaments in their amplifiers?
http://www.diyaudio.com/forums/tubes-valves/168994-cc-vs-shunt-filament-supply.html
However, there is the possibility that someone you like listening 50Hz/60Hz, and its harmonics...😀
There is a saying "There is no amplifier, better than its power supply"😉
In the old days, capacitors were costly, especially electrolytics, was common at that time see huge chokes, and huge electrolytic capacitors of... 10 uF.
By then it was common practice to use AC on the heaters, and this habit, passed from generation to generation.
Today, there are other things such as MOSFET transistors, operational amplifiers, Schottky diodes, etc.
It's called "Progress"...
It's been a lot of electrons under the bridge.😀
I was also a newbie once, at that time there was no Internet, only old books, old circuits, and old habits...
I was rescued from my confusion by the Dutch, with its magazine "Elektuur", since then I have no doubts in using DC on the filaments.
I want to remark that this thread is not about a particular assembly, but what happens inside the valves.
The demonstration on post # 98 is not very orthodox, neither elegant, but it could be a useful warning about the use of AC in the filaments.
But as Julius Caesar said when he crossed the electrolytic
Alea iacta est
I'm just a TV repairman, nothing I say could convince you...🙄
But what if a superhero of the forum, use DC on filaments in their amplifiers?
http://www.diyaudio.com/forums/tubes-valves/168994-cc-vs-shunt-filament-supply.html
However, there is the possibility that someone you like listening 50Hz/60Hz, and its harmonics...😀
If there was any I wouldn't like it - since there isn't I will stick to AC heaters
Shoog
So far we have not considered the effect of the resistance and capacitance between cathode and heater.
An elegant presentation on the subject
http://www.diyaudio.com/forums/tube...itors-cathode-preamp-tubes-5.html#post3216284
If that does not convince you, nothing will...
An elegant presentation on the subject
http://www.diyaudio.com/forums/tube...itors-cathode-preamp-tubes-5.html#post3216284
If that does not convince you, nothing will...
Last edited:
If that does not convince you, nothing will...
It doesn't. From the spec sheet of a type I've used before: 6FQ7:
Grid to (H + K) -- 2.4pF
No indication as to what the capacitance between the heater wires and cathode are, but even if it was two orders of magnitude greater: 240pF:
Xc= 1 / (2pi * 60 * 240E-12)= 11.05M
The cathode resistor was: 68K (cathode follower) so what's that voltage division?
68E3 / (68E3 + 11E6)= 0.006= -44db
That would be a worst case scenario, and I highly doubt there's 240pF between the cathode and heater. You don't have to start worrying about heater isolation until you're well above the shortwave frequencies. (6M and below)
For highly sensitive RF applications (e.g 6AL5s used as passive ring mixers, or other "front end" applications such as active mixers) then DC heater power might make sense, as you wouldn't want any 60Hz leaking through at microvolt levels to modulate the incoming RF. Even there, you're talking about ~100dbv of amplification from antenna to loudspeaker, distributed between AF gain stages and IF gain stages.
It might apply to some low level, high gain, AF systems like preamps for MM or MC cartridges. For designs that operate at the usual line levels (tape decks, CD players, MP3 players, sound cards, etc) it's not necessary to DC power the heaters of IDH type VTs.
For line level projects, I've tried it both ways: AC heating and DC heating. It made no difference, even with the AC heater supply left floating to avoid a possible Vhk problem.
Wow ! -44dB, for a Cathode Follower ! Only due Ckf ! Impressive numbers !
Lack consider Rkf, and the induction phenomenon is even more important...
BTW. If AC makes you happy, go on...😉
As Argentine proverb says:
Tastes are tastes said an old woman and sat on top of an anthill...😀
Lack consider Rkf, and the induction phenomenon is even more important...
BTW. If AC makes you happy, go on...😉
As Argentine proverb says:
Tastes are tastes said an old woman and sat on top of an anthill...😀
That's ignoring the output impedance of the CF too, which will probably be <1k, bringing the attenuation to better than -60dB...
Hola loco, tenés razón, pero mira lo irónico del caso, no estoy hablando sobre mis prejuicios, sino sobre hechos medibles.
Muchas, pero muchas veces, en la fft de un ampli, se puede ver claramente, este boludo alimenta los filamentos con alterna...
Lo mas loco es que hay "Expertos" que pretenden tapar el sol con la mano.
Lo mas triste es que hay gente que viene al foro en busca de aprender, y cuando se dan con cosas como esta, terminan mas confundidos que cuando entraron.
Yo solo soy un reparador de TV, pero algunos "Expertos" son Ingenieros Electrónicos, hasta profesionales diseñadores de Audio y eso es algo que me cuesta entender.🙄
Te podes imaginar el RTP3C de Allen Wright, con los filamentos alimentados con alterna?
Una locura, no? 😀
A lo mejor la frecuencia de la red y sus armónicos tenga su encanto...😀😀😀
Hello buddy, you're right, but look at the irony, I'm not talking about my prejudice, but on measurable facts.
Many, many times, in the fft of an amp, you can clearly see, this guy powered the filaments with AC...
The crazy thing is that there are "Experts" who claim to cover the sun with the hand.
The sad part is that there are people who come to the forum for learn, and when given with things like this, they end up more confused than when they went.
I'm just a TV repairman, but some "Experts" are Electronic Engineers, professional Audio designers and that's something difficult to understand.🙄
Can you imagine the RTP3C from Allen Wright, with filaments powered with AC?
Crazy, right? 😀
Maybe the mains frequency and its harmonics has its charm...😀😀😀
Muchas, pero muchas veces, en la fft de un ampli, se puede ver claramente, este boludo alimenta los filamentos con alterna...
Lo mas loco es que hay "Expertos" que pretenden tapar el sol con la mano.
Lo mas triste es que hay gente que viene al foro en busca de aprender, y cuando se dan con cosas como esta, terminan mas confundidos que cuando entraron.
Yo solo soy un reparador de TV, pero algunos "Expertos" son Ingenieros Electrónicos, hasta profesionales diseñadores de Audio y eso es algo que me cuesta entender.🙄
Te podes imaginar el RTP3C de Allen Wright, con los filamentos alimentados con alterna?
Una locura, no? 😀
A lo mejor la frecuencia de la red y sus armónicos tenga su encanto...😀😀😀
Hello buddy, you're right, but look at the irony, I'm not talking about my prejudice, but on measurable facts.
Many, many times, in the fft of an amp, you can clearly see, this guy powered the filaments with AC...
The crazy thing is that there are "Experts" who claim to cover the sun with the hand.
The sad part is that there are people who come to the forum for learn, and when given with things like this, they end up more confused than when they went.
I'm just a TV repairman, but some "Experts" are Electronic Engineers, professional Audio designers and that's something difficult to understand.🙄
Can you imagine the RTP3C from Allen Wright, with filaments powered with AC?
Crazy, right? 😀
Maybe the mains frequency and its harmonics has its charm...😀😀😀
I haven't seen any "measurable facts", especially the stray capacitance between heater and cathode. If this was so critical, then why is it not in the spec sheets? How is it that you don't see heater isolating RF chokes being used with GG amps and CFs until you are well below the upper end of the ham bands (10M)? If you're gonna make the case that it makes a difference, then give us some figures. What is the actual magnitude of this capacitance?
How do you know this? There are ways for AC to get into the output: magnetic "conduction" from a PTX (especially the more aesthetically pleasing "drop in" types) through a steel chassis to an OPT. Stray capacitance from the primary of a PTX around a filter chain (especially choke input with the choke in the DC return). Undetected oscillation in one stage that radiates into the PTX (diodes also make excellent mixers). Hell, I've seen tiny 60Hz pips in the FFT of solid state amps that don't have heaters.
The crazy thing is that there are "experts" who put all their effort into scoring points and worrying about that which is not worth the effort instead of concentrating on optimizing where it'll actually do some good. We already know that if you're gonna go the DC route, you'd best make certain it's clean DC. Dirty DC is worse sonically than AC. If you have IDH VTs, and line level input signals, AC or DC won't make any meaningful difference. Just make sure you reverse bias the slightly N-type semiconductor that red hot aluminum oxide becomes, and you're good to go.
If you're discussing DHTs and DHPs, then we can start a whole nother cat fight: AC v. DC v. voltage regulated DC v. constant current DC v. high frequency AC -- all of which have their supporters and detractors who'll never arrive at a consensus.
I exposed the facts, if you want measurements, do it yourself, that is not my duty here.
If you take the trouble to read, the thread is not about to post # 126, but if you are concerned about Ckf
http://tubedata.itchurch.org/sheets/010/e/ECC81.pdf
http://tubedata.itchurch.org/sheets/030/e/ECC88.pdf
http://tubedata.itchurch.org/sheets/030/e/ECC186.pdf
http://tubedata.itchurch.org/sheets/117/e/EC8020.pdf
http://tubedata.itchurch.org/sheets/010/e/EL34.pdf
I recommend you also read "Valve Amplifiers" by Morgan Jones, (Chapter 5 in third edition) explains there better than me...
There you can also find heater isolation RF chokes.
If we talk about some more or less serious design/build, if the fft shows two peaks of IM in 50Hz (60Hz) / 100Hz (120Hz), it's unmistakable symptom of AC powered filaments.
If the amp is doubtful origin, one can expect anything as the source of hum, then I momentarily disconnect filaments, if the hum disappears immediately, the filaments are responsible.
But this is very basic, you should already know it.
There is no amplifier, better than its power supply.
It seems to me that you don't have made your best effort powering heaters.
If you can't design a clean DC heater supply, I recommend the standard LM317, "A la Morgan Jones", or a very original approach with LM317/LM337 "A la SY"
http://www.diyaudio.com/forums/diya...oise-thoroughly-modern-tube-phono-preamp.html
I don't think that you would like my own PSUs, are too complicated. 😀
Mire don popilín, hear you please that Osvaldo from Banfield talked to the group. A couple of things. The true is the true and is supported from scientific findings and probably one big thing is the model that support them.
There were one reason much important that we talk by phone. When the heaters were developed for indirect heat valves, much and very much energy the engineers made and put in the bench. The valves and its cathodes became more efficient and more cheap the devices became cause with this cathodes they didn't need of make DC in those times, in focus more with the economic factors as than the quality.
If in those times you want get this DC type one, you needed Big rectifiers, and big capacitors and there Was an mission impossible neither "Lalo Shifrin couldn't listen good music.....
Right now the way is too but too different. You can get monster capacitors, diodes and regulators. The people of Audio Freaks don't hesitate nothing at the hour of get DHT and expensive vacuum tubes rectifiers, shunt regulated power supplies that waste energy and ticked the CO2 layer in the atmosphere only because they like class A amps for find "That theoretical Sound" that at the end of the story is impossible to determinate because at the end of the story "is a Subjective experience"
Now I have hum, stupid hum in my recently got Sansui 1000A. And I just replace all the capacitors from the power supply doubling the values because is easy. And the 6AN8 I have are so sensitives to the Heater hum. How much must I need to put DC there? I can do it this afternoon with a couple of tribulations.
With this example I try to explain that is easy to put DC in heaters and avoid to fight after with another problems, only cause the engineer tried to avoid the hum twisting the filaments and did declare in the books than this valves "could use with AC". But these were not a Decree from the engineers.
Now is cheap and easy to use DC with all the benefices. The audiophile that persist in use AC there is free and belong to the field of extravagances that human been uses. Please big friend, don't waste your time, you convince to me and many others but always you gonna have detractors. But one more thing .
At the end "the doubt", this mechanism is the source in find more info from the physical phenomenas.😀😉
Best Regards
Hi Dady, good to see you around here !
My dear friend, you never cease to amaze me with your advice and comments, not to mention your Audio work, designing, building, tweaking, repairing...
Turntables, CD players, amplifiers, and your magnificent DIY speakers !
And you are a Medical Doctor !
Chapeau !
And yes, you are right, I'm wasted my time, the only hope I have is that people who come for help can find something useful, all of us were "newbies" once.
I don't want a "sound" in my amps/preamps, I go valves only for linearity, not for fashion.
However, I don't own the truth and also want to learn.
In this case "the doubt" is about why the venerable Kondo San, among others, used AC powered heaters, even in DHT.
Even when you can not only measure, but hear the damn hum.
Having seen so many reports about the "warmth" and "musicality" of AC powered heaters, I was looking for a somewhat more founded response.
Never found it.
I could only make some basic physical/mathematical conclusions, but nothing more...
Although I have my suspicions about the effects of modulation, my limited knowledge in electronics is insufficient to make any conclusive statement, remember that I'm just a TV repairman.
Audio listening experience is some subjective, so put equations here is very difficult.
Maybe mains frequency and its harmonics have their own "warmth/musical" charm after all...
Nevertheless I will continue using DC on heaters, it has null derivative, so more chance to avoid a "sound". 😀
My dear friend, you never cease to amaze me with your advice and comments, not to mention your Audio work, designing, building, tweaking, repairing...
Turntables, CD players, amplifiers, and your magnificent DIY speakers !
And you are a Medical Doctor !
Chapeau !
And yes, you are right, I'm wasted my time, the only hope I have is that people who come for help can find something useful, all of us were "newbies" once.
I don't want a "sound" in my amps/preamps, I go valves only for linearity, not for fashion.
However, I don't own the truth and also want to learn.
In this case "the doubt" is about why the venerable Kondo San, among others, used AC powered heaters, even in DHT.
Even when you can not only measure, but hear the damn hum.
Having seen so many reports about the "warmth" and "musicality" of AC powered heaters, I was looking for a somewhat more founded response.
Never found it.
I could only make some basic physical/mathematical conclusions, but nothing more...
Although I have my suspicions about the effects of modulation, my limited knowledge in electronics is insufficient to make any conclusive statement, remember that I'm just a TV repairman.
Audio listening experience is some subjective, so put equations here is very difficult.
Maybe mains frequency and its harmonics have their own "warmth/musical" charm after all...
Nevertheless I will continue using DC on heaters, it has null derivative, so more chance to avoid a "sound". 😀
Well I have read all posts of this link, but dont see the answer to the question about AC or DC in the heaters, I have finished the change today in my amp 6c33 with 6ac7 in the preamp stage.
I only have change the preamp filaments to DC with FM317 regulator.
I adjust to 6,2v DC
here nobody say what happend with the sound when you change AC to DC..........
when you change the filaments to dc you have a different amplifier with differents details of the music I dont know if is better but sure is different I need more time to have a conclusion about this changes.
I only have change the preamp filaments to DC with FM317 regulator.
I adjust to 6,2v DC
here nobody say what happend with the sound when you change AC to DC..........
when you change the filaments to dc you have a different amplifier with differents details of the music I dont know if is better but sure is different I need more time to have a conclusion about this changes.
IMHO, the only difference would be a mainly hum and a little hiss diminution when using DC heating instead of AC, with all the rest of the circuit being indeed perfect about hum and hiss before, otherwise you could not tell the efficiency. Here is what I do :
- this is worth to do in phono and preamp sections.
- this is worth too when heating directly-heated tubes like 10Y/VT25, 50, 2A3, 300B for perfect quietness.
- this is compulsory on tube guitar overdrive pedals indeed.
- For power section, it is useless if the tubes are cathode heated : a GND CT reference is enough (or equivalent).
Here is my OTL amps (built in 1993, still alive), with all the tubes heated on AC, the 4x6080 being heated on 6.3VAC, totalizing 10A. The preamps 12AX7/U7 are on 12.5VAC, with positive reference to GND (+50VDC AFAIR) in order to maintain F/K voltage above the datasheet's limit.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I never noticed any difference in sound or tone due to DC or AC heating, at least on preamp section. But yes, there may be a little one on directly-heated tubes, possibly due to a slight modification of the curves tied to filament steady polarity ? I noticed nothing significative in that field...
A+!
After one day listen the amp with the change in the heater to DC, you must know that the 6ac7 is a pentode e little rude in high frequencies this normal in every pentodes in the preamp stage. Well after the change to DC now the amp is different in details and timbre, I am a maniac of the details and the micro information but is true that same times the excess of info change to rude same passages of music. With this amp the piano and violins at high frequencies and volume is a little rude now after the changes is very smooth but too I have lost small info, the music is less spectacular but is most true. The balance is that know I will follow with the dc heater, I will begin to adjust again the coupled capacitor to try to recuperate more details as I like, maybe the K40 will replace by Teflon ft3.
- Status
- Not open for further replies.