GoodSoundClub - Romy the Cat's Audio Site - Lower hum on 6C33C preamp.

10-05-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	41
Post ID:	17120
Reply to:	17119

The Golden 6C33C in house.

I unpacked the Gold Grids 6C33C that I got from Bulgaria. Upon very meticulous inspection I did not find that they were in any way different then the regular grid tubes. I did not open a tube to check it further. It is possible that the Bulgarian guy just BS us and sold the regular tubes, but what the difference now? It is what it is. He did not lie about the fact the some of them are used. I have 5 used tubes among the 13 that I got. Just for fun I put all of 5 used tubes in Milq LF channel. Melquiades in fact acts as VERY accurate tube tester for 6C33C. I can intently measure current at normal bias and gain – all that I care. All 5 used tubes did measure very well, in fact almost like new. Just for fun I took one new tube and put it stone cold at 60W just after 2 min of heating filament. Presumably the tube Gold Grids shall prevent in this case grid secondary emission. The tube was fine but it not prove the presence of the Gold Grids as I have seen plenty of regular 6C33C that do not need any pre-manipulations. Well, I guess I will be using them like any other 6C33C. I got too excited that they are “special” tubes and I think it was a mistake. I paid twice more then I have to, but I am sure it was not the first and not the last time when I paid for excitement. It is time to grow up…

Rgs, The caT

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

10-05-2011

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Paul S
San Diego, California, USA
Posts 2,656
Joined on 10-12-2006

Post #:	42
Post ID:	17122
Reply to:	17120

Eccentric but Reliable?

As I've mentioned elsewhere before, over the years I've gotten about 25% clinkers, among all tubes, from all sources, including "specially selected, graded and matched" tubes. Also, I have lived with the 6C33C enough to say it "drifts" in use, and if i ever built an OTL, the 6C33C would be one of the last tubes I would consider for it. So how funny is it that - now that I think about it - I have NEVER - so far - gotten a 6C33C that was bad right out of the chute! While the "boutique" versions seem no better - practically speaking - than the garden variety 6C33C, neither are they any worse. And so far every 6C33C I have put in the ML2 has been useable, and all have "done their jobs" to the extent that I only think about them when it comes time to re-bias.

Paul S

10-05-2011

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KOTriode
Posts 40
Joined on 07-20-2010

Post #:	43
Post ID:	17123
Reply to:	17120

Fuses on the tubes save the day.

Last weekend, just for fun, I brought the amp and preamp to the 2011 Burning Amp in San Francisco. On the first speakers, the Audio Kinesis, I let the heater warmup for about 15 min, and then switched on the power, the amp was fine, we played for about 1/2 hour and stopped. About couple hours later we wanted to try on the Field Coil Lowther, I plugged the amp and warmed up the heater, a friend was so excited and ask me to skip the heating period and turn on the power. So I did, the heater was probably warmed up less than 2 minutes. It start to play fine for about 5 minutes, and the tube was biased at 180ma, about 3 minutes later, the left channel pop the 250ma fused I installed at the plate, then 2 minutes later, the right amp fuse blown. I thought, Romy was right about heating this tube for an hour before playing. But 60W after 2 min, I probably wont try that!
When I got home, I installed new fuses, the amp worked fine. Later in the evening, I turned on the amp again and listen to music. When I reached to grab the volume pot on the 6C33C preamp, my right hand sleeve got caught wit the tube and knock the preamp tube out of the socket (while music was playing), the right speaker make a not so loud noise as someone would expect when pulling a preamp output tube. What happened was that the 250ma fuse in the pamp was blown when the preamp tube jumped out of the socket.
The 250ma fuse probably did save the tubes and speaker on those two occasions.

10-05-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	44
Post ID:	17124
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The fan did not last.

I never had any fuses in my amp and never had any need for it. I have a fuse at my DHT channel as the tube is rare but not on the 6C33C. I do not really understand the problem you have with current. You have the meter that shows you current in real time. Your tune the amp, put current for lest say 50mA and wait what will be the max currant. In 10-20 min it will be let say 200mA. Then you set your cruising current of lest say 300mA and forget about it. In a few weeks, as your tube will burn in you will add more current as the max rise of current will not reach 300mA. That is it. There is nothing else that need to be done with this tube. You need to bias the well hot tube, not the tube that just was turned on a few minutes ago.

BTW, my fun with the Golden tune did not last too long. I left in my amp one of the used Bulgarian tube and in 2-3 hours it begin to give to me pings in bass channel. This was the sigh that the tube is completely worn out, despite that it give current as it was a new tube. Before disposing the tube I broke it, took it apart and inspected the Gold Grid. The grid was absolutely black. He wire might be golden but it was covered with thick burned sediment residue. I am not sure that regular 6C33C would not have the same golden-like grid.

I never bough any used tubes and I can not believe that I have bought used 6C33C. To buy used 6C33C is like buying used toilet paper. Still, I did it…. I think the Bulgarian’s trick about the golden grid did blinded my brain.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

10-06-2011

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KOTriode
Posts 40
Joined on 07-20-2010

Post #:	45
Post ID:	17125
Reply to:	17124

Fuse: just a precaution on 6C33C

Romy,
I added the fuse recently just for protection for the output transformer since these 6C33C tubes plate current can get very high and might damaged them. Also DC coupling on this high gm tube can cause plate current to go max if something failed. I never used fuse at the plate with other tubes, even big transmitting tubes such as 845, Eimac 250 .... even using dc coupling.
I did not know that the Bulgarian tubes was used, if I knew, I would not have bought it, but the seller did refund one of my bad tube.
I am still burning in the second set of tubes on my amp which has about 15 hrs playing time. The preamp tube is OK so far, it is much easier on the tube since it draw only 18ma and use only one triode.

10-25-2011

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Matossan
Posts 1
Joined on 10-25-2011

Post #:	46
Post ID:	17225
Reply to:	17027

6C33C preamp - Kotriode

Few weeks ago, I had the chance to visit KOtriode and listen to his system but more specifically his Preamp. The preamp use half of the 6C33C per channel (one 6C33C has two triodes). It has two outputs, one is transformer coupled output, the other is choke load (through transformer primary ) with capacitor output. The gain is about 8db, adequate for a preamp. The preamp has regulated DC supplies, uses only oil capacitor, no electrolytic. It also has a remote control, with 4 inputs, the pot is motorized Alps. The overall aesthetic presentation of this device is stunning but more important the sound is deeply involving with a great sense of openness in the full bandwidth. The first set-up was using the digital output of his tube Dac and bypassing the preamp. Though the intrinsic characteristic of naturalness was still here the sound was a bit more condensed and less seamless vs. using the preamp. In other words all the tiny glary aspect was gone yielding an effortless and highly compelling sound. I was much impress by the “humanistic” aspect of the sound bringing certain poetry to all the music that we listened. Anyway, I thought I will share this with you as it is only too rare to have the opportunity of hearing such a conclusive playback!

Cyrille

10-25-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	47
Post ID:	17226
Reply to:	17225

Was it preamp or DAC’s volume control?

Cyrille, thanks for the comments. The KOtriode’s 6C33C preamp is certainly a unique thing and not a lot of people have reference how it might sound. Not it is too complex but rather not a lot of people have balls to make preamp out 6C33C. In fact years back I made jokes out if it but here it come - homebody made it and look like you like the it’s sound. As I told I would love to hear it by I have too small testacals to undertake such a project…

The question I would ask however: how did you QE the volumes for bypass test? You said that you use digital output of your DAC to manage volume and you said that preamp has 8db of gain. So, I presume with preamp is you max out the DAC and use the preamp’s motorized Alps to set volume. This is fine. However, if you use no preamp then you had no volume control and the only way for you was to use the seemingly digital volume control of your DAC. By advised that the digital volume controls are more or less transparent ONLY if they are max out open. If you set a digital volume control for a fraction dB down then the entire signal is wasted. So, would it be possible that the advantages you hear in 6C33C preamp were partially due to the fact that your DAC’s digital volume control was maxed out, meaning was in bypass?

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

10-25-2011

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KOTriode
Posts 40
Joined on 07-20-2010

Post #:	48
Post ID:	17230
Reply to:	17226

The Sound of 6C33C preamp.

Romy, No, the DAC was not set at maximum level (for best sound) while Cyrille listening to the system. It was set at normal volume for the whole system.

When Cyrille dropped by, I was showing him the Field Coil open baffle speaker system which consist of a 12in Supravox woofer, 2 Supravox 215 Field coil and 8 ribbon tweeters per side ,the system efficiency is about 100 db/w. The power amp used was a 20W 845 for the Supravox, an 8W 845 SE is used for the ribbons. This is normally a tri-amp system, but on that day, it was setup as a bi-amp system to test the 6C33C amp, since them 6C33C amp is not yet broken in, I decided to use the 20W 845 SE. The source was a DIY wireless DAC with tube output (and pretty low output impedance). I played quite a few different tracks to show him what the system can do.

Just before he left for New York, I want him to hear the new 6C33C preamp (not fully break-in with just 5 hrs on the clock). What I did was inserting the preamp between the DAC (without changing the DAC level) and amplifiers and then set the preamp so the volume is about the same (the preamp act more like a buffer now).I choose three tracks that we played earlier, Temptation by Krall, La Boheme live by Aznavour, and the Firebird by Eiji Oue Reference Recording. We listened to the tracks, remove the preamp and re-inserted it about 3 times.

What we both discover is that with the preamp the soundstage is much larger (by about 25%) and extend way beyond the speaker edges, there is also more depth when listening to Aznavour live track. The tonal balance is not that much different except that Tempation track, the bass was deeper, the midrange tonal balance remain the same, but there is so much more detail and speed, the high was smooth and much more extended through the ribbons.

This is for me an unexpected result, since I was expecting tonal balance to change with this 6C33C preamp or any additional amplification stage, it wasn't in this case.

The preamp was not without fault. On this 100db system with 8ft away from the speaker there is a faint 60Hz hum, on the bench the hum was measured at about -58db which is quite high. My guess is that the hum came from the transformer and was picked up from the chassis, since like most power tube when using in a preamp, there is much higher microphonic than small 9 pin or octal tube. There is more work to be done to eliminate the hum. I will probably try to mount the tube sockets on some kind of rubber minimize vibration from transformers.

10-26-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	49
Post ID:	17231
Reply to:	17230

About preamps and the preamp.

That was very interesting post, here are some thoughts of my about it.

KOTriode wrote:
Romy, No, the DAC was not set at maximum level (for best sound) while Cyrille listening to the system. It was set at normal volume for the whole system.

Ok, it was not at it optimum sonic level but at least it was at identical level of digital degradation for no preamp test and with preamp in the signal path. If so then it was fine.

KOTriode wrote:
What we both discover is that with the preamp the soundstage is much larger (by about 25%) and extend way beyond the speaker edges, there is also more depth when listening to Aznavour live track. The tonal balance is not that much different except that Tempation track, the bass was deeper, the midrange tonal balance remain the same, but there is so much more detail and speed, the high was smooth and much more extended through the ribbons.

From what you describe I can conclude that your DAC is not good. You said you use DIY wireless DAC with tube output. I do not know what wireless mean in this context, but it is not important. I also know do not like any tube output stage in DACs, I have written about it extensively. Anyhow, my rational to blame your DAC is following: the sonic changes you describe shall not take place if your DAC is able to drive your power amp properly. It is not only about output impedance. Something in that DAC’s out stage does not work properly as a good preamp much not make a difference as you witnessed. With very good preamp you might have a little better dynamics and slightly better bass but it shall be all. If you witnessed so dramatic soundstage change, change in detail and speed and higher extension of HF then you are just way beyond of definition of preamp transparency. Are you sure that what you observe was not change in cables or something like this?

KOTriode wrote:
This is for me an unexpected result, since I was expecting tonal balance to change with this 6C33C preamp or any additional amplification stage, it wasn't in this case.

As I said above, if I got the result you did then I would revise what my front end outputs. Find another DAC, of phonostage of CD player with DC-coupled SS output stage, it shall not be any good devise but any consumer unit would do. Do the same experiment with insertion of your preamp. You most like will not has the same difference.

KOTriode wrote:
The preamp was not without fault. On this 100db system with 8ft away from the speaker there is a faint 60Hz hum, on the bench the hum was measured at about -58db which is quite high. My guess is that the hum came from the transformer and was picked up from the chassis, since like most power tube when using in a preamp, there is much higher microphonic than small 9 pin or octal tube. There is more work to be done to eliminate the hum. I will probably try to mount the tube sockets on some kind of rubber minimize vibration from transformers.

Oh, this is nothing. I am sure you will find out the problem and address the hum. The hum must not be there, the preamp shall be dead silent and with indirect heated 6C33C it is very simple to do, particularly with regulated circuitry. Beside the standard ground loop procedures and dealing with ripples you might want do not let the undirected heaters to hang without reference to gerund…

Rgs, The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

10-26-2011

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KOTriode
Posts 40
Joined on 07-20-2010

Post #:	50
Post ID:	17234
Reply to:	17231

Dac output stage.

Romy the Cat wrote:
From what you describe I can conclude that your DAC is not good. You said you use DIY wireless DAC with tube output. I do not know what wireless mean in this context, but it is not important. I also know do not like any tube output stage in DACs, I have written about it extensively. Anyhow, my rational to blame your DAC is following: the sonic changes you describe shall not take place if your DAC is able to drive your power amp properly. It is not only about output impedance. Something in that DAC’s out stage does not work properly as a good preamp much not make a difference as you witnessed. With very good preamp you might have a little better dynamics and slightly better bass but it shall be all. If you witnessed so dramatic soundstage change, change in detail and speed and higher extension of HF then you are just way beyond of definition of preamp transparency. Are you sure that what you observe was not change in cables or something like this?
As I said above, if I got the result you did then I would revise what my front end outputs. Find another DAC, of phonostage of CD player with DC-coupled SS output stage, it shall not be any good devise but any consumer unit would do. Do the same experiment with insertion of your preamp. You most like will not has the same difference.
Rgs, The Cat

I was not satisfied with commercially available DAC output stage neither, so I built something a little bit different.
The output stage of my DAC is direct coupled to a gain stage, again directly coupled to a cathode follower using an KT66 tube and capacitor coupled to the output. It is not normal to have an KT66 output tube as the DAC final stage, but I like it sonically this way compare to a number of other tubes that I tried. This DAC output impedance while not as low impedance as the 6C33C, is pretty low (about 200 ohms) and can drive about the same mount of current as the 6C33C preamp, and there is only 5 feet of cables to drive to the amp, so I was pretty puzzled by the sonic result when inserting the 6C33C preamp in the chain.

10-26-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	51
Post ID:	17235
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I think you will do more experiments….

KOTriode, I was not criticizing your DAC, whatever it is. I was saying that system-design-wise if your preamp was able to inflict such a dramatic change in Sound then in my view it just highlighted the problem with DAC. Take another DAC, or any commercial CD/DVD player from your kinds room, or a phonostage or a tuner or a tape-machine of any another front end you have and try to make the same experiment. It will instantly give you the idea if what you observe is the preamp generic sound or it was the weakness of preamp to drive your speakers directly. General what you describe is very common for DACs that has passive output stage, or just one transformer right after decoder…..

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-02-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	55
Post ID:	17289
Reply to:	17285

Yes, that sucks...

KOTriode wrote:
It's 60Hz hum, caused by both mechanical and magnetic field coupling to the output transformer. I used a toroidal transformer and thought it would not caused this problem but it did. When using an external power supply for both B+ and heater (AC), the noise went down to around -74db, another 12db improvement. The output transformer is 1:1 and does not have magnetic shield, it picked hum easily. So, for now I just use the preamp the way it is, but in the future, if I build another 6C33C preamp, which I certainly will, I will have the power supply on separate chassis.

Well, the sexy configuration of your chassis does certainly have toll. Whatever I even built, no matter how little it was used separate chassis for transformers and power chokes with the last cap on the control chassis. Well, I did built one headphone amp that had all together but that project went to nowhere as it sounded like crap.

I think with use good cans it is still possible to mount a good toroidal in soft wax and to hide it mechanically and magnetically from the rest of the circuit. It for sure shall not be sitting in the middle of chassis…

BTW, one very important think, did you check your PS for incoming DC? Toroidals are notoriously horrible if they see any DC on primary. Most of the RMS meter will not measure DC properly with 120AC, at least my Flukes do not do it. so, you might run juts for teat the am from some kind of 1:1 isolation transformer and to see it comfort your in chassis toroids. I have a good success to place the transformer on the fat sheets of sorbotan and isolated them with MuShield sheets. Still, nothing can beat the transformers sitting in … basement and rung a long cable to control unit. The long cable in this case acts as a wonderful decupler between the filtering stages….

The caT

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-02-2011

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Romy the Cat

Boston, MA
Posts 10,155
Joined on 05-28-2004

Post #:	57
Post ID:	17294
Reply to:	17292

Regarding your transformers, make it flipable.

Ah, you use those gorgeous VPI boxes to host transformers. No wonder it does not sound well, what did you see the anything from VPI sound well? Seriously, I do have those VPI boxes, I do not remember where they come from to me but they are too good to wasted them and I keep in them cartridges mounting hardware.

Regarding your transformers. You might do what I did with my Melquiades. When I made my Super Melquiades 6ch chassis I was not experienced with the fact that it will be too many and too powerful transformers and chokes in there at very close proximity. So, I had quite a lot of mechanical noise. The Melquiades chassis is very strong – 4mm steel. Now I understand as it was a mistake and it had to be me non-ferromagnetic material for PS chassis. For the control unit there is nothing better than steel but the PS I would go only aluminum.

Anyhow, to redo everything was too much pain in ass and I kept fighting with mechanical noise coming from stray felids of my transformer and chokes.

http://www.goodsoundclub.com/Site_Images/SuperMilq5.jpg

Then when I a few year I went for toroids I came with a cool idea to lift the transformers from the surface of chassis and to orient their stray fields parallel to the chassis and perpendicular to each other. The frame the attached the toroids to chassis I made from aluminum.

http://www.goodsoundclub.com/Site_Images/SuperMilq_6Ch_3.jpg

so, today I have 4 small pieces of magnetic inside:

http://www.goodsoundclub.com/Site_Images/SuperMilq_6Ch_50.JPG

and 8 outside:

http://www.goodsoundclub.com/Site_Images/SuperMilq_6Ch_53.JPG

The noise is very low, practically negligible is there is no DC in power lines but I use PP2000 that have my ass with DC.

So, you might do something similar or even kinkier. Put your power transformer in a can or on the box you have it now but make the cable that run to chassis loose. Then attach an expendable arm from chassis to transformer can that would flip and extend the transformer from the chassis. If you go very crazy then you can put a micro switch under the transformer and as the transformer sit in it default transporting position then the amps is off and if the transformer is lifted and extended off the chassis then the amp turn on.

Rgs,
Romy the Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-02-2011

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KOTriode
Posts 40
Joined on 07-20-2010

Post #:	58
Post ID:	17296
Reply to:	17294

It's OK for now.

I used those VPI magic brick sitting on top of the transformer, my audio analyzer tell me that these bricks helped the noise by about 1db, may be the 6 lbs or so weight does damp the xformer vibration, so I leave them on, just trying everything to keep the hum low.
You have a good point about changing the position of the toroidal, I have thought about standing it up, but the wire I cut was too short to move the transformer. The hum from magnetic field must be pretty high from these toroidal, because when I remove the can and the toroidal is exposed naked, the hum was higher by 3db!
For now, the hum level is slightly audible, good enough for me to go on and compare the 6C33C preamp sonic to other. Onto the 6C33C amp, on my second set of tube (not the golden grid), which has about 50 hrs of playing in the amp, are pretty stable now, the bias current reach to the exact 200ma setting after about 15 minutes every time, so far no surprise.... I never have problem with hum in this amp, I guess with the step down ratio of 600:4, it is not sensitive as the preamp 1:1 in therm of noise and magnetic field.

03-14-2012

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KOTriode
Posts 40
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Post #:	59
Post ID:	17962
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6C33C amp/preamp follow up

Wow! I did not realized that almost 4 months have passed since I wrote last.
Quite a few things have happened the last 4 months that I have played with the 6C33Camp/preamp combo. I have tried at least 3 different vendors on the Ulyanovsk type, the Gold Grid plate (from Bulgaria) and Svetlana. The amp ran without any problem, I have modified the amp power supply by changing the power transformer to a beefier 400W toroidal, twice as much VA, so that I can experiment the 6C33C tubes with plenty more current and voltage. I changed the rectifier tubes from 5R4WGY to 5AR4. I ran the output tubes at around 220V and 240ma, that's about 53W of plate dissipation. The Bulgarian tubes after about 60 hrs of playing, showed instability in bias on both tubes, the current would changes every 15 minutes after I bias them to 220ma sometimes it will go up to 240ma, sometimes go down to 200ma, tube bias just dont want to stay put. After I got 20 new Svetlana tubes, I picked random 2 tubes, burn-in the heater for about 5 hrs, put on power, biased them at 230ma, it will stay the same times after times of power up and during long listening session. I have played more than 50 hrs on the Svetlana and quite happy with them. Few days ago I checked prices of these tubes, and was surprised that the asking price now is twice of what I have paid (and from same seller!) . The 6C33C Ulyanovsk in the preamp dissipate 6W of plate power ,worked without any problem, and very stable bias current. These 6C33C are suprising low in microphonic for an output tubes, I would say its microphonic level is as low as a good 9 pins or octal tube and much lower than any other output tubes.

I started to break-in the preamp/amp mostly with DAC sources but change to vinyl at about the 100 hrs mark and up to now, I believe I am familiar with the 6C33C tubes sound characteristic.

- Upon listening, one would recognize these 6C33C has huge and big sound, not too different from 845 tubes in what Romy characterized as Elephant Sound which not many other tubes that I have tried shares this same trait, and it is the main reason that I like the sound of 845.- The second character that stand out the most of the 6C33C tubes is the schockingly level of micro detail and focuses that these tubes revealed without adding a touch of brightness to the music when listening to a recording like John Klemmer Arabesque from Nautilus direct-to-disc. On a guitar recording of Kiyoshi Shomura playing Danza Espanola on the first cut, you can clearly hear the sound of the guitar string plucked and each breath the artist takes when playing. By comparison the 845 sounded dark and the leading edge transient is soften.- On dynamic, the 6C33C tube showed its ability to go deep in the bass on Ray Brown trio recording of Soular Energy which is excellent for a 15W SE , the 845 amp can do better, but not by much, but probably because of its 25W output give it more headroom than the 6C33C.- One always think that you have to use directly heated triode to get the best midrange out of a tube amplifier, the 6C33C proves that it is no longer necessarily true. The 6C33C is simply so revealing and coherent on pair of stacked Quad, it just sound much better than many amp in my stable, and that's include a pair of Futterman OTL 3.

- Distortion: the 6C33C is not very linear, in audio amplifier it exhibits the highest level of distortion than any power tube.

The 6C33C tube got to be the best buy tube in history, it provide so much level of musical enjoyment for such a price. In a multi-amp system, I would prefer to use the 6C33C for midrange and high, 100Hz up, I think it's hard to beat the 6C33C it's unfortunate that its power output is inadequate to power woofer even with one 100db/w sensitivity.

03-14-2012

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Romy the Cat

Boston, MA
Posts 10,155
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Post #:	60
Post ID:	17964
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Feedback to the 6C33C review.

KOTriode wrote:
On dynamic, the 6C33C tube showed its ability to go deep in the bass on Ray Brown trio recording of Soular Energy which is excellent for a 15W SE , the 845 amp can do better, but not by much, but probably because of its 25W output give it more headroom than the 6C33C. .

I do know the sound of 845 and 211 tubes and I feel that properly implemented 6C33C shall way over-perform them in dynamic and bass. The advantage that 845 has is by the fact that it is a 845 direct heated tube and by definition the direct heated might gently enter the grid currents and run in A2. 6C33C in contrary is indirect heated and it even theoretically can’t operate properly with grid currents. If eve if you give to 6C33C super powerful driver than as soon swing in grid approaches the bias voltage the tube will just clip. The direct heated do not clip, the run higher distortions but the still are operational in A2. This gives to people who do not care HOW the amp running a feeling that 845 has more bass sand more dynamic. The reality is that one need to be certain if the sensitivity of his acoustic system is enough to be able to use 6C33C in A1 , if not then all bets are off. I was laughing to see the idiots big-Willson user who claim that that bough Lamm ML3 and feel that it has more dynamic and more bass then Lamm ML2.0. I did ask them if any of them ever seen on scope what happen when 18W Lamm SET begin to drive the dead 15” Willson ported woofer. Of cause they have no idea what I even asked – they are too “big” reviewers to pay attention to such “small” things. Anyhow, if the 6C33C is not stressed to A2 then I do feel that 6C33C has better bass then any 845 I heard.

KOTriode wrote:
One always think that you have to use directly heated triode to get the best midrange out of a tube amplifier, the 6C33C proves that it is no longer necessarily true. The 6C33C is simply so revealing and coherent on pair of stacked Quad, it just sound much better than many amp in my stable, and that's include a pair of Futterman OTL 3.

I do not necessary agree with it. The “best midrange” is a complex subject. I have absolutely no problems with 6C33C midrange but there is more to it. If you run multi-way installation then you have you own custom objective to the sound of MF channels. You change the compression driver; crossover, you play with wires and with many other aspects, I went even further and added tonal injection as I was not able to get tone I needed from one MF. The 6C33C has very nice and clean midrange but it has only one type of midrange. If one would like to add own specific twist into out of midrange MF channel then 6C33C, in my view, does not give a lot of options. You can get many different productions of 6C33C and they all will sound the same more or less. With directly heated triodes we have fallibility to find the character we want among many options. As I went for DHT I was paling with dozens of different tubes unit I found the one that doe the best in context of the rest of my efforts. If you compare the 6C33C midrange with the midrange on my current MF DHT tube (YO186) than the DHT will be laughable. I guess it produced a huge amount of distortions but you would never seen a person who walked out of my room and did not claim the it was the cleanest and the most interesting MF s/he even heard. The point that I am trying to make is that in context multi-ampling the 6C33C is not the most flexible tubes if one goes for any custom characters for given channel. The 6C33C is very clean and too straight forward for “some” applications.

The caT

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

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