Hello everyone,
I have a single ended 211 power amplifier that used to have AC heaters on the 211, and then got 'upgraded' to have DC heaters from the same AC transformer output at 10.5V.
This occurred around 20 yrs ago and I can't recall why (I think it was considered a good idea at the time). The circuit is super simple 47000 uF cap to ground, 0.82R in series followed by a 47000 uF to ground with a 2.2 uF Wima bypass. The original balance pot on the cathode remains in place but obviously there is very little AC left and whilst it can be used to sort of reduce the minimal hum it does not really make much difference.
The amp is pretty quiet and causes no problems BUT I keep reading about the better SQ of AC heated filaments in DHT and I have no memory of the before and after DC heater with this amp, it was a long time ago and I was not actually using it then, a friend was.
So for a morning or probably more like a days work and some cable to try this - what do you think, likely to be beneficial in terms of potential sound quality improvements or likely to make very little difference apart form adding some hummmmm!
Thanks for sharing your thoughts and experience
I have a single ended 211 power amplifier that used to have AC heaters on the 211, and then got 'upgraded' to have DC heaters from the same AC transformer output at 10.5V.
This occurred around 20 yrs ago and I can't recall why (I think it was considered a good idea at the time). The circuit is super simple 47000 uF cap to ground, 0.82R in series followed by a 47000 uF to ground with a 2.2 uF Wima bypass. The original balance pot on the cathode remains in place but obviously there is very little AC left and whilst it can be used to sort of reduce the minimal hum it does not really make much difference.
The amp is pretty quiet and causes no problems BUT I keep reading about the better SQ of AC heated filaments in DHT and I have no memory of the before and after DC heater with this amp, it was a long time ago and I was not actually using it then, a friend was.
So for a morning or probably more like a days work and some cable to try this - what do you think, likely to be beneficial in terms of potential sound quality improvements or likely to make very little difference apart form adding some hummmmm!
Thanks for sharing your thoughts and experience
Who in their right mind builds a TUBE amp with 47,000uF x2 of filtering?
That's utterly rediculous.
That's utterly rediculous.
Lol, it's for the filaments.
Anyhow. People claim AC sounds better but if you look at the output you'll see harmonics visible. The bottom line is whatever you think sounds better.
these are both 47000 16V....and it was done by a professional who makes and sells amplifiers. I have no experience to comment!
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In my experience (I've built three SE 845/211 amps) it's going to be too noisy--distractingly so. I used a common-mode choke in the filament supplies, which gave them a smoother sound. You could add some here if you want to, or you could swap in one of several regulated supplies available for DIYers, but otherwise I'd leave it alone.
I've used 10,000uF capacitors for a four tube 12AX7 preamp unregulated filament supply, and there was still significant ripple.
Scaled up, that's equivalent to the 211 with a 100,00uF capacitor in the filament supply.
You do. It's intermodulation between the AC heating (Line frequency, plus overtones against the signal). The sidebands are easily visible, if you take spectrum of the output. The IMD products have no relation to any natural distortion, so it does not help to make an overall natural sound.
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Okay, the heater circuit heats the filament (or heater in indirectly heated tubes). So it would be more sensitive to higher frequency noise on that supply. A clean AC supply is much more efficient than a DC supply, and fewer filter capacitor issues down the road. If you use a regulated supply for DHT heaters you will have less opportunity for noise.
Now. Time to think of the system. The gain in DHT circuits is low. Especially in output circuits. That means that noise in this supply is less of an issue than it the supply powered earlier tubes that had more gain afterwards. To be honest, we can measure noise below 120 dB below -10 dBV, or 1 watt pretty easily these days (I can go much lower). However you really can't hear much below -80dB (look at your room noise for an idea of dynamic range). Therefore, while improvements can be made, and may be much talked about, realistically these improvements won't buy you anything.
What this means is that your choices should be more concerned with reliability as long as noise levels are adequate. These tubes were designed in an era where performance was awful compared to what we easily achieve today. So techniques used back then had relaxed performance goals. While we can get much higher performance today, and it is worthwhile - to a point, don't get caught up in extreme levels of performance. You simply will not hear it.
Sound quality. That depends entirely on the signal path as long as you don't have problems in HV supplies or heater supplies. So for sound quality, you're concentrating on transformer quality, stabilization of the circuit and layout (believe it or not). Circuit design is a major factor of course. Don't confuse sound quality with filament supplies or HV supplies (as long as they are problem free).
-Chris
Now. Time to think of the system. The gain in DHT circuits is low. Especially in output circuits. That means that noise in this supply is less of an issue than it the supply powered earlier tubes that had more gain afterwards. To be honest, we can measure noise below 120 dB below -10 dBV, or 1 watt pretty easily these days (I can go much lower). However you really can't hear much below -80dB (look at your room noise for an idea of dynamic range). Therefore, while improvements can be made, and may be much talked about, realistically these improvements won't buy you anything.
What this means is that your choices should be more concerned with reliability as long as noise levels are adequate. These tubes were designed in an era where performance was awful compared to what we easily achieve today. So techniques used back then had relaxed performance goals. While we can get much higher performance today, and it is worthwhile - to a point, don't get caught up in extreme levels of performance. You simply will not hear it.
Sound quality. That depends entirely on the signal path as long as you don't have problems in HV supplies or heater supplies. So for sound quality, you're concentrating on transformer quality, stabilization of the circuit and layout (believe it or not). Circuit design is a major factor of course. Don't confuse sound quality with filament supplies or HV supplies (as long as they are problem free).
-Chris
I wonder what the ripple current rating is on those 47000uF 16V capacitors is?
I put a 22000uF 35V cap on the 12.6V DC heater supply on a HK cit I (9 12ax,at7's)back in the
early 80's, I didn’t check the ripple current rating on the caps, that lasted about a week.
I put a 22000uF 35V cap on the 12.6V DC heater supply on a HK cit I (9 12ax,at7's)back in the
early 80's, I didn’t check the ripple current rating on the caps, that lasted about a week.
It's simple. Those pushing ancient technology are not technically savvy for one. Two, it is an expensive, inefficient technology where certain folks can make a lot of money. Three, it does sound completely different and maybe some people like that compared to current "not great" products.
In any event, people like this sound some times. It's a choice or personal preference, so you can't argue it.
In any event, people like this sound some times. It's a choice or personal preference, so you can't argue it.
http://v2.stereotimes.com/post/audio-note-ongaku-integrated-g70-preamp-and-ge1-phono-stage
The 211 valve has a great sound quality reputation, and has a very linear output for a single ended design, so it's used for these reasons.
It can easily be shown that with DC heating of a filamentary cathode the current at the negative terminal is by the sum of plate and screen current higher than the current at the positive end, regardless whether there's a »balancing« trimpot, regardless where the filament is grounded. Aside from the fact that this must end in unequal cathode wear, the plate current needs to flow through the heater PSU if the filament is grounded improperly (= not at it's negative terminal). Hence the heater PSU may well affect the amplifier's performance.
The best way is AC heating, with the heater winding CT'ed. It doesn't show any of these disadvantages. This is how it has been and still is done with big transmitting or modulator tubes.
Best regards!
The best way is AC heating, with the heater winding CT'ed. It doesn't show any of these disadvantages. This is how it has been and still is done with big transmitting or modulator tubes.
Best regards!
So, I'm supposed to believe in what some audio website review says?
I don't, sorry.
Their opinions and praises mean nothing to me as an experienced old audio tech.
Because those audiophile reviewers are PAID to say nice things, regardless of the product's actual performance or specs.
But you go ahead, buy into that hype, it's your money.
You asked why an old transmitter valve is used in a power amplifier and I was providing a bit of context and history as this particular amplifier was one of the first to use this valve and has a somewhat iconic status. I have no opinion on the integrity of the review, and like the majority of the population have no intention of spending ridiculous sums on an amplifier. I do however use the same valve in my own one because I enjoy the sound, on a much more modest budget 🙂
I agree. However, in a single-ended amp noise is going to be an issue with AC filaments, especially with a 10 volt filament. There are ways to overcome this imbalance, one being a bipolar filament supply, or some of the DIY regulator boards I mentioned above. Many, many SE amps use DC filament supplies for the output tubes and I don't think this uneven cathode wear, under the circumstances, is that big an issue. I built an SE 845 amp with DC filaments for a friend 20 years ago and he still uses it without issues. I think he replaces the 845s every few years. Maybe they would last longer with AC filaments, but the trade-off would be an unacceptable noise floor.
An amplifier with a DHT (Direct Heated Triode) output tube.
Here are some examples of what you get:
1. DC on the filament; with a flute playing a note, Concert A 440Hz
The flute has its note, and also naturally produces some harmonics.
Flute fundamental 440Hz, some 2nd harmonic 880Hz, and some 3rd harmonic 1320Hz.
Sounds just like a flute.
The amplifier may have some 2nd and 3rd harmonic of its own too, but so far we only have 3 frequencies.
All is well, and we can relax and enjoy listening.
Good
2. AC on the filament; 60Hz power mains; with a flute playing a note, Concert A 440Hz
440Hz, 880 Hz, 1320Hz, but you get something more, because of AC heating: 2 X 60 Hz = 120 Hz.
You will get 120Hz sidebands on each an every note and on each and every harmonic.
440 - 120 = 320Hz; 440 + 120 = 560Hz
880 - 120 = 760Hz; 880 - 120 = 760Hz
1320 -120 = 1200Hz; 1320 - 120 = 1440Hz
Not very good
3. Well, suppose you have 50Hz power mains. The results are very similar.
50 x 2 = 100 Hz
So, 440 - 100 = 340Hz; 440 + 100 = 540Hz
880 +/- 100
1320 +/- 100
You get the idea
Not Good
If you use AC heating on an input tube, driver tube, output tube that is a DHT, you get the same additional tones.
Have you ever played an amplifier so loud that it is very near to drawing grid current.
With AC DHT, it will draw grid current, at 2 x the power mains frequency.
The sidebands that appear below and above each and every musical tone, and each and every musical harmonic (overtone) will be very loud (120Hz or 100Hz)
Not Good
Now, when is the last time on Tubes / Valves threads that you heard a posting that claimed his DHT amplifier with DC powered filaments was burning up his output tubes?
If you did, it was not because of using DC on the filaments.
Instead, there was:
Too much plate to filament B+
Too much plate current
Too much plate Watts dissipation (plate volts x plate current)
Too much filament voltage
Or trying to use more grid current in Class A2 than the grid was rated for (more likely for an Audio tube Versus RF tubes, or RF/Audio tubes).
Happy listening to your DC powered DHT 211 tubes.
By the way, are the 211 tubes burning out way to often???
They are not, Right?
Ha Ha to the burning out to early theory. Practice is all that matters.
One more thing . . . a tube that is linear, but that has 100Hz or 120Hz sidebands on each and every music fundamental tone, and each and every overtone . . . all those upper and lower sidebands does not make a linear amplifier, no matter how 'linear' the tube may be (a linear tube used in a less than linear mode).
Just my opinions
Here are some examples of what you get:
1. DC on the filament; with a flute playing a note, Concert A 440Hz
The flute has its note, and also naturally produces some harmonics.
Flute fundamental 440Hz, some 2nd harmonic 880Hz, and some 3rd harmonic 1320Hz.
Sounds just like a flute.
The amplifier may have some 2nd and 3rd harmonic of its own too, but so far we only have 3 frequencies.
All is well, and we can relax and enjoy listening.
Good
2. AC on the filament; 60Hz power mains; with a flute playing a note, Concert A 440Hz
440Hz, 880 Hz, 1320Hz, but you get something more, because of AC heating: 2 X 60 Hz = 120 Hz.
You will get 120Hz sidebands on each an every note and on each and every harmonic.
440 - 120 = 320Hz; 440 + 120 = 560Hz
880 - 120 = 760Hz; 880 - 120 = 760Hz
1320 -120 = 1200Hz; 1320 - 120 = 1440Hz
Not very good
3. Well, suppose you have 50Hz power mains. The results are very similar.
50 x 2 = 100 Hz
So, 440 - 100 = 340Hz; 440 + 100 = 540Hz
880 +/- 100
1320 +/- 100
You get the idea
Not Good
If you use AC heating on an input tube, driver tube, output tube that is a DHT, you get the same additional tones.
Have you ever played an amplifier so loud that it is very near to drawing grid current.
With AC DHT, it will draw grid current, at 2 x the power mains frequency.
The sidebands that appear below and above each and every musical tone, and each and every musical harmonic (overtone) will be very loud (120Hz or 100Hz)
Not Good
Now, when is the last time on Tubes / Valves threads that you heard a posting that claimed his DHT amplifier with DC powered filaments was burning up his output tubes?
If you did, it was not because of using DC on the filaments.
Instead, there was:
Too much plate to filament B+
Too much plate current
Too much plate Watts dissipation (plate volts x plate current)
Too much filament voltage
Or trying to use more grid current in Class A2 than the grid was rated for (more likely for an Audio tube Versus RF tubes, or RF/Audio tubes).
Happy listening to your DC powered DHT 211 tubes.
By the way, are the 211 tubes burning out way to often???
They are not, Right?
Ha Ha to the burning out to early theory. Practice is all that matters.
One more thing . . . a tube that is linear, but that has 100Hz or 120Hz sidebands on each and every music fundamental tone, and each and every overtone . . . all those upper and lower sidebands does not make a linear amplifier, no matter how 'linear' the tube may be (a linear tube used in a less than linear mode).
Just my opinions
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