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09-20-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 26
Post ID: 17028
Reply to: 17027
6C33C... the beast
fiogf49gjkf0d
Shame on you Romy, you took them all without leaving some for others!I am waiting for the shipment of these tubes, I only bought 3 to try it out in my amp. In the meantime, I am running my amp with the rest of these unknown qualities from Asia with filament burned for more than 20 hrs before applying any current, and I am running them conservatively at 160ma when listening to music, will see what happen.Surfing the web, I found few places that sell Svetlana brand for less than $20, not in the 50's range, so that might worth a try too. Yes you were right, it wont be the last $50 I will spend on these tubes, I might need couple dozen more of them for future uses since I am starting to cook something new with this beast.
09-20-2011 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,571
Joined on 10-12-2006

Post #: 27
Post ID: 17029
Reply to: 17028
"Boutique" 6C33Cs
fiogf49gjkf0d
Here's an obliquely-related related anecdote:  It has been 2 years since I put a pair of "quasi-boutique" 6C33Cs in the boost position in my ML2s.  I know, I "should" change them to regulation, just to be safe; but now I have become morbidly interested to see just how long they will last as amplifiers.  I cannot say they "sound better", or anything like that; and of course they need to be re-biased regularly, like any garden variety Ulyanov.  I would deem the longetivity a fluke, but both of them are still going strong (...knock on wood...).  While I'm thinking about it, I should also mention that (as always) I cleaned the pins carefully and greased them lightly prior to use, and I may have pulled them for cleaning and re-greasing maybe twice since I first put them in.

To be clear, I do NOT recommend anyone else leaving any 6C33C in 50+ Watt boost position this long, and if you hear "popping" from your 6C33C, pull it and toss it immediately.

Best regards,
Paul S
09-20-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 28
Post ID: 17030
Reply to: 17028
Do abuse your 6C33C.
fiogf49gjkf0d
KOTriode, I got a feeling that your unfortunate experience with the few presumably bad tubes that and your former experience with DHT tubes made you to treat the 6C33C as it is some kind of fragile princess. Filament burned for more than 20 hrs before applying any current? It is not some kind Marconi PX4 that you bought for $1700 and afraid to fart near it. The 6C33C is indirect heated and it was made to care very abusive treatment. After a few hours of the new tube the large swings of bias stop and the tube might be consider as mature. Do abuse the 6C33C. The good thing about the 6C33C is that if you very much preserve it then it will die in a year but if you treat it rough then it will not live longer than 12 month…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-20-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 29
Post ID: 17031
Reply to: 17029
Never had any problems at 50W+
fiogf49gjkf0d
 Paul S wrote:
To be clear, I do NOT recommend anyone else leaving any 6C33C in 50+ Watt boost position this long….

To be clear, I have ML2 with 6C33C in 50+ Watt and the amps were running some for days without shutting down – not problems at all. Furthermore I have no Milq’a midbass channels and it runs at 290mA and around 195V that make 56W. I can tell you that Melquiades sometime is running for VERY long time, sometime I live hopme and do not shut down the amps, I still never had any problems….


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-20-2011 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,571
Joined on 10-12-2006

Post #: 30
Post ID: 17032
Reply to: 17031
Chronic Chronicity
fiogf49gjkf0d
Who said there were problems running the tube over 50W?  I am saying outright that I recommend swapping tubes run this hot after 1 year, as a matter of course, just as a "precaution".  Since I have just passed 2 years at about 53W, this is one case where it can happen.  But I am not "recommending" this practice.  YMMV, etc.

BTW, I think I paid the princely sum of 56USD/pr for the quasi-boutique 6C33Cs, and part of this is that I want "to get my money's worth".

Best regards,
Paul S
09-20-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 31
Post ID: 17033
Reply to: 17030
6C33C preamp
fiogf49gjkf0d
Romy,Nah, I just want to careful with what I have left, dont want to have an amp without tube for now. The gold grid tube probably take a while to get them. From what I remember from a tube dealer who said that these 6C33C need to have the heater burn for many hours before apply any current, if not the tube will have shorter life. On my next mono block,  I will push them hard to get at least 25W with less than 5% distortion, that means run 2 tubes in parallel, but only one triode in each tube. 

In the mean time, this is what I am cooking for the last few days.... to drive my 6C33C amp, while burning in the 6C33C leftover.

6C33Cpreamp.JPG
09-21-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 32
Post ID: 17034
Reply to: 17033
Cooking with 6C33C, literally.
fiogf49gjkf0d

The 6C33C preamp? Hm, this is bold. As I see you use it as a single stage buffer with only one 6C33C and couple output with a transformer? I head the Germans built something like this but I never heard it or saw it. I do not feel a need for such a preamp, even though I drive very complex load.  Still, it is for sure interesting. When you fill conformable then writhe how it sound, particularly in context of a mandatory for any preamp bypass test. BTW, I can see in the back of the amp two tubes, looks like regulators. One of the tubes has getter all eaten up. I usually do not use the tubes with so dramatically eaten getter.

 KOTriode wrote:
From what I remember from a tube dealer who said that these 6C33C need to have the heater burn for many hours before apply any current, if not the tube will have shorter life.

What your dealer advised is fine:  you can burn 6C33C heaters for many hours before apply any current.  I disagree that it will prolong the tube live but it will minimize the current swing during the tube break in. I do not recognize the current swing in the new 6C33C as a problem and I have given dental instructions how to deal with it:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=6140

Let look at in the process deeper. Reportedly when the 6C33C were made and the oxide-coated cathodes was activated some of the oxide contaminated grid that in a new tube begin to act as second emission devise in new tubes. As the tubes begin operation the oxides on the grid begin to burn out producing gases that are eaten by getter.  It is not know if the problem with 6C33C is due to the contamination of grid or die to the large amount oft left over gas in the balloon. In one way or another it looks like the heating up the tube for prolong time before running it at full power do help. It burns oxides from grid if they have any and it heat up getter, letting it to absorb gas from the tube.

What I do not feel comfortable, purely from practical perspective, is a recommendation to run the tube for a long time with heaters only. If you have a separate chassis to burn the 6C33C filaments then it would do but to do it on your main amp it is bit too irrational in my view. You need to put a separate swatch in the amp to hold the high voltage and you need to take the amp out of operation for long time – how you will listen music if your amp is busy with tube burning? With the same success you can get a party of your new 6C33C and dump them into kitchen oven at 320 degree for few hours. This will activate getter to do it’s duty and will help with some grid pre-burn.  To put the tube into the kitchen oven? Ok, not we are talking about the pure cooking with 6C33C. BTW, do not forget to put in the over some Italian herbs and paprika….

My methodology is much simpler in my view and do not take amp out of operation. Put the new tube at 20-30mA and in 30-45min you will have the max current swing the give tube will be able to demonstrate. You need to lower current constantly during the first 30-45min as it will/might go up and up. In my estimation what you start from sub 50mA you will not have during the first turn on more then 250-300mA. Eventually you will reach the point where currant does not grow. It will be it. This is the max swing. From now start to use the tube as useless. With the time, 12-70 hours of initial operation you will see that the current will be dropping and dropping, drop bias and give to tube more current.  The point is that if you use your amp let say 3 hours a day then it will let you to have your amp for 1-2 weeks perfectly operational while the 6C33C will be breaking in.

 KOTriode wrote:
On my next mono block,  I will push them hard to get at least 25W with less than 5% distortion, that means run 2 tubes in parallel, but only one triode in each tube. 

Why would you need it? I do not see any rational behind it.

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
09-21-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 33
Post ID: 17035
Reply to: 17034
6C33C as single triode.
fiogf49gjkf0d
The preamp has the classic tube regulated power supply using 5R4, 6AS7, 6SJ7. It is transformer coupled output and has no capacitor in the signal chain, the gain is about 8db, so it is not a buffer. For convenience, it does has a remote control. It is still in the work, but will be able to sing pretty soon. 

The 6C33C preamp and amp has only one power switch, both has two transformers, one for just the heaters, the other for B+ and regulated supply. When plugged in, the heater will light up first, when flipping the power switch, the B+ will start slowly with the regulated power supply. Without hitting the power switch, I can burn in the new tube filament over night .

The rational behind using two 6C33C with one triode in each tube is that it will allow you to have a total of up to 90W plate dissipation for two tubes instead of 60W using single tube or for higher reliability (according to the spec) 3000h with 70W versus 45W two tubes. Another feature is that I will be able to use the amp with 1 tube and adjust the bias for 45W dissipation for less demanding speaker ( Quad ESL 57).  Also my output transformer is rated with 350ma/30W so it should be interesting to squeeze more power out of it. For me it is a very convenient feature. By the way the preamp only use one triode instead of both. I always like using output tube in preamp, to me  it is sonically superior to the small 9 pins and octal tubes, the only downside is the microphonic.
I will report the sonic quality of the preamp/amp in the future.
09-22-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 34
Post ID: 17037
Reply to: 17035
The half life of 6C33C and 6C33C preamp.
fiogf49gjkf0d

 KOTriode wrote:
The preamp has the classic tube regulated power supply using 5R4, 6AS7, 6SJ7. It is transformer coupled output and has no capacitor in the signal chain, the gain is about 8db, so it is not a buffer. For convenience, it does has a remote control. It is still in the work, but will be able to sing pretty soon.

The 6C33C preamp and amp has only one power switch, both has two transformers, one for just the heaters, the other for B+ and regulated supply. When plugged in, the heater will light up first, when flipping the power switch, the B+ will start slowly with the regulated power supply. Without hitting the power switch, I can burn in the new tube filament over night .

The rational behind using two 6C33C with one triode in each tube is that it will allow you to have a total of up to 90W plate dissipation for two tubes instead of 60W using single tube or for higher reliability (according to the spec) 3000h with 70W versus 45W two tubes. Another feature is that I will be able to use the amp with 1 tube and adjust the bias for 45W dissipation for less demanding speaker ( Quad ESL 57).  Also my output transformer is rated with 350ma/30W so it should be interesting to squeeze more power out of it. For me it is a very convenient feature. By the way the preamp only use one triode instead of both. I always like using output tube in preamp, to me  it is sonically superior to the small 9 pins and octal tubes, the only downside is the microphonic.
I will report the sonic quality of the preamp/amp in the future.

I see, I got confused with your using the phrase “6C33C with one triode”. I usually use this wording for pure double triodes what you can use them separately. Unfortunately it is not the case with 6C33C. The two half of 6C33C have separated contacts for heaters, but no ways driver separately anodes but cathodes. This is kind of bitch, I have no idea what they did this way. So, what we talk about use of half of 6C33C we do not use one triode but rather a half of triode by disengaging filaments from “other” side. BTW, if you like this type of operation then you might like to try 6C41C. You do not need to change anything with that tube and juts plug it into the socket that just drew the half of 6C33C.  The 6C41C is a single heater tube with exact half of 6C33C. I truly do not like the 6C41C sonically in power amp but your mileage might wary and who knows, it might be in preamp it might work out. The preamp duty is not the same as power amp duty….

The microphonic 6C33C in your preamp? This is interesting. I never use the 6C33C in the line level situations and therefore I never had the situation that it might behave microphonic. Try to put a small rector before grid and put some ferrite bids before the grid pin. Also, try to shut down temporarily your fans that cool down the 6C33C from the bottoms (it would be noise to have a picture of it).

I also like preamps with very powerful drive but I am with the world of SS preamps with direct coupling. I found that it would be very interesting to listen the 6C33C preamp. What kind transformer you get for it. Also, I do not know where you live but if you in US’s East cost and ever come to Boston then I would very much do not mind if you bring that 6C33C preamp for a few hours to let me to hear the beast. I have no idea how it might sound but the notion to have 6C33C in preamp sound too absurd to pass the opportunity to hear it. Too absurd? Well, this is very much in my alley…

The biggest question would be if the half of 6C33C is as good at line level buffer as let say 2-4 of small 9 pin tubes. You also have that output transformer that is controversial aspect. I kind of do not feel at ease with line level output transformers, but it is me….

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
09-22-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 35
Post ID: 17041
Reply to: 17037
Killing two birds with one stone with the 6C33C preamp
fiogf49gjkf0d
The transformer in this preamp was given from a friend who want to learn how to wind transformer. If I remember correctly it started out as UBT, they were bought (when UBT was operating in the Silicon Valley) at the company swap meet. They were rejected (for frequency response) and was sold for $10, we were told that it can be used as a plate load . So my friend bought them and rewind them as an interstage, the last time he used it for a 211 tube and was not to happy. After more than 10 yrs sitting in my garage, I took it to the bench and load it with the 6C33C at 100V/25ma, it turned out the frequency response was not that bad after all, I presumed that the real low impedance of the 6C33C tube result in a wider bandwidth than using it with the 211 which impedance is 50 times higher. 
If you looked at the preamp chassis, you will see that there are 2 set output RCA per channel. My original intent was use it as choke load capacitor coupled preamp, the second output was added after checking the bandwidth as the transformer coupled (I think it was down only -1db or so at both end of the spectrum) on the bench. Killing two bird with one stone... I thought.
I am in California, but if the 6C33C preamp 's sound is up to my expectation, I wouldn't mind shipping it out to Boston for a week of vacation.
PS: Basically you can use any 1:1 transformer with current you want to run the transformer at.




09-24-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 36
Post ID: 17061
Reply to: 17041
6C33C Golden grid tube.
fiogf49gjkf0d
Just in time. After about 5 hrs of music on the preamp , I received today the 3 golden grid tube. Looking with a magnifying glass, I could not determined if it is gold wire. Anyway, I am burning the heater and will try out tomorrow. Here are some picture of tube and grid wire..

goldengrid.JPGgoldengrid.JPG


img_5965a.jpg

10-04-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 37
Post ID: 17116
Reply to: 17061
2 out 3... not bad.
fiogf49gjkf0d
After burn-in the heater for 24 hrs, I tested all 3 Golden grid tubes on a bench power supply , 2 of the tubes worked fines, 1 tubes does not have current. The tube seller gladly refund for the non functional tube.
I talked to a 6C33C OTL amp manufacturer in the far east and learned that about 20% of the tubes he received are not usable, he added that the good ones seemed to run reliably well.

10-04-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 38
Post ID: 17117
Reply to: 17116
20% of faulty 6C33C!?
fiogf49gjkf0d
KOTriode,

We had this conversation before. It is not what I regularly experience. The 20% of faulty tubes is astonishingly high number for this tube and if he has this ratio and did not change his suppliers then he must be crazy. On the good side you know where his 20% of faulty tubes go – you bought them!
On another note, your amp manufacturer makes OTL with 6C33C. The OTLs are very different animals and the requirements for the tube are much tight. Still, no matter what you do the OTLs with 6C33C do burn the speakers, soon or later but they will.

Anyhow, I do not agree with that 20% of faulty tubes assessments. It just does not correlate with what I experience with this tube. I have the Golden Grid tube already in here, I got a dozen of them, but I did not open them up.

BTW, when you say that the “tubes does not have current” what does it mean? If you keep dropping bias then you do not have current rising?

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
10-04-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 39
Post ID: 17118
Reply to: 17117
6C33C tube.
fiogf49gjkf0d
Romy,
The normal bias for the Golden Grid tube for 200V Plate at 200ma is about 70V-80V for the good tubes, the bad tube read 0ma at this bias, when drop to -30V it start reading some current, but can't get to 150-200ma current for the SE amplifier.
The people who make the OTL amp that I talked to also see abnormally higher number of new 6C33C tube out of spec and unusable than other Russian tube such as GM70, pentode family. He also added that he has seen an OTL amp used in a store played 18 hours a day every day and the tubes lasted for 3 years.


 
10-04-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 40
Post ID: 17119
Reply to: 17118
You are not lucky with them.
fiogf49gjkf0d
 KOTriode wrote:
Romy,
The normal bias for the Golden Grid tube for 200V Plate at 200ma is about 70V-80V for the good tubes, the bad tube read 0ma at this bias, when drop to -30V it start reading some current, but can't get to 150-200ma current for the SE amplifier.
The people who make the OTL amp that I talked to also see abnormally higher number of new 6C33C tube out of spec and unusable than other Russian tube such as GM70, pentode family. He also added that he has seen an OTL amp used in a store played 18 hours a day every day and the tubes lasted for 3 years.
 
I do not remember correctly but I think a normal bias for 6C33C is 55V-80V but if you have at 30V juts some current but not a good 0.5A then something IS wrong with the tube. This is very strange. KOTriode, you are understood that I am not in the business of support of the 6C33Creputation. Still, I can only report what I observe and I did not observe any problem with this tube. I did also observed very sever abuse of this tube and the situation when the tube refused to die. The GM70is VERY different tube, triode not pentode and GM70 is much more reliable tube and stable in characteristic, in fact it is the most stable then probably any other, but what it has to do with anything?  I do know people who have 6C33C running in amps days and days. When I had 4 ML2 I sometime did not turn them over long weekends – it is 8 tubes. I run Mils with 8x6C33C for days and I find the 6C33C is very reliable. In my view the problem with reliable is not reliability by stability of parameters and high run out of characteristics with new tubes. Anyhow, I am sorry that you look like not so lucky with those tubes. BTW, the Bulgarian guy told me that all of his tube are pulls, not the new tubes…
 


"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 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 41
Post ID: 17120
Reply to: 17119
The Golden 6C33C in house.
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,571
Joined on 10-12-2006

Post #: 42
Post ID: 17122
Reply to: 17120
Eccentric but Reliable?
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 43
Post ID: 17123
Reply to: 17120
Fuses on the tubes save the day.
fiogf49gjkf0d

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 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 44
Post ID: 17124
Reply to: 17123
The fan did not last.
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 45
Post ID: 17125
Reply to: 17124
Fuse: just a precaution on 6C33C
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
Matossan
Posts 1
Joined on 10-25-2011

Post #: 46
Post ID: 17225
Reply to: 17027
6C33C preamp - Kotriode
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 47
Post ID: 17226
Reply to: 17225
Was it preamp or DAC’s volume control?
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 48
Post ID: 17230
Reply to: 17226
The Sound of 6C33C preamp.
fiogf49gjkf0d
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 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 49
Post ID: 17231
Reply to: 17230
About preamps and the preamp.
fiogf49gjkf0d

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 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-20-2010

Post #: 50
Post ID: 17234
Reply to: 17231
Dac output stage.
fiogf49gjkf0d
 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.
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