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09-15-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-19-2010

Post #: 21
Post ID: 17010
Reply to: 16993
6C33C reliability disappointment!
fiogf49gjkf0d
Totally disappointed today, while I was listening to music, the left channel make a small pop and quit. The bias meter showed about 25ma bias instead of 200ma. Test the tube on bench showed that the tube current stay about 25-50ma max. This tube is gone abrubtly instead of slow death after 31 hours of playing. Took another brand new tube and plug into the amp with just heater power on, nothing! Turn out a brand new tube has dead heater, amazing! Take out another tube, heat the filament for an hour, and check the bias, this time it is less than 100ma, another goner.   

Check reliabilty of 6C33C on the net and found this:

I can also sell you a carton of 50 for $900, including ground shipping within the continental US. At this price they are "as is" - I will not replace any which are broken, out of spec or dead  (they're a bargain anyway). Reports suggest you can expect 10-20% to be significantly out of spec.

So, it looked like that these tubes left the factory untested and it is up to the buyer to sort them out.

I order some " Ulyanov " tubes on Ebay, anybody have tried them yet? What label of these tubes proven to be reliable?

It is unfortunate that there are reliability issues with these tubes, the last few hour of music showed that the 6C33C has great potential, I was enjoying the music it was making  and drawned up plan for a pair of 6C33C's mono block.
09-15-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 22
Post ID: 17011
Reply to: 17010
Reliability and stability of 6C33C?
fiogf49gjkf0d

Well, I would say that “something is wrong” as what you report it is not how it shall be. I had my doubts about the rational to use 6C33C in direct heating coupling but the “danger”
 in direct coupling uselessly coming from the plate of the driver tube and from breaking of PS sequencing. Abyhow, I think the problems you are experiencing now are normal for new amp and exposure to new tubes. As both of them mature you shall not have those problems. Let look at what we have in the hands.

 KOTriode wrote:
Totally disappointed today, while I was listening to music, the left channel make a small pop and quit. The bias meter showed about 25ma bias instead of 200ma. Test the tube on bench showed that the tube current stay about 25-50ma max. This tube is gone abrubtly instead of slow death after 31 hours of playing.

I would call it unlikely. Sure any tube can catastrophically fail and you might be unlucky in this case but I would say that it is most likely not what happened. I would rather blame your regulators and PS then the tube. From the mid 90s I use 6C33C. I use a few BAT amps, few Lamms and few Milqs, in all cases it was multi-amping and I went over many of 6C33C. I have perhaps 2-3 tubes that failed with what I call “catastrophe”. So, I fell the reliability is not the factor for 6C33C at all, in fact it is VERY reliable tube. The stability of the parameters is totally other mater – it might be anything you can imagine but still the tubes with ran way paramagnets in my view are perfectly operational.

Make sure that your PS are reliable and that you do not loose bias supply “at the mid of the night”. Then the sequencing. Here is how it must be: 1) heat the filaments for at least 2 min 2) Apply bias and lock it value. 3) Apply plate voltage. I do not know how bias your 6C33C but I presume that it might have some kind of bug that kills your 6C33C.

 KOTriode wrote:
Took another brand new tube and plug into the amp with just heater power on, nothing! Turn out a brand new tube has dead heater, amazing!

Never had it I think. What I has however was that the new 6C33C have the pins covered with some kind of protective anti-corrosive shit that does not conduct electricity. It is not to mention that if you use bad tube sockets then the heater female pins might burn up very fast (not after 31 hours of playing of course). So, you need to make sure that you clean/scrub the 6C33C pins what you put need tube in. If there is no ignition on the filament then jerk the tube in the socket vaoalsntly and it will scrub the pink and you will have your filaments back. It is not DHT tube and the filaments are not fragile in this tube. It is impossible to shake this tube to the point that filaments will be damaged.

 KOTriode wrote:
Take out another tube, heat the filament for an hour, and check the bias, this time it is less than 100ma, another goner.

I do not recognize it as goner. This is very normal and all that you need to do is to drive bias down until the tube gives to you your expected current. The bias amount is absolutely irrelevant for this tube. You might have initial 45V or 110V – that all is normal. As the tube get break-in the bias amount will more come to the more or less expected value. KOTriode, if you remember in my initial reaction to your design I was very skeptical in your idea of direct coupled of 6C33C. In direct coupled applications the plate of driver acts as bias of the output stage. If you are accustomed to nice DTH with stable and predictable expectation of bias then this might not work with 6C33C as this tube has one parameter that is absolutely irrelevant: bias voltage.  Take a look in the tube you need to have stable gain (self-explainable), stable plate current (as it set plate impedance). The only one parameter that is not being seen by your speakers is bias. In the situation with fix bias I would like to have max control over bias and unfortunately in case of direct could you have no room to maneuver. If I am right then I have no pleasure in it but if you insist to be direct coupled then you might do some creative tricks. You might for instants to intrude with kind of supplementary bias. It means the let say 50V would come from your driver tube and another adjustable 50V would come from your supplementary bias. This way you will have option to accommodate any 6C33C. In Melquiades can play absolutely any 6C33C. In fact I select the tubes in Milqs ONLY by their gain and I never pay attention to the bias voltage. No matter what current the tube gives when it new I know that I have always reserve bias to set it to be at the expected current.

 KOTriode wrote:
Check reliabilty of 6C33C on the net and found this:
I can also sell you a carton of 50 for $900, including ground shipping within the continental US. At this price they are "as is" - I will not replace any which are broken, out of spec or dead  (they're a bargain anyway). Reports suggest you can expect 10-20% to be significantly out of spec. So, it looked like that these tubes left the factory untested and it is up to the buyer to sort them out. I order some " Ulyanov " tubes on Ebay, anybody have tried them yet? What label of these tubes proven to be reliable?

OK, a few things. It is possible, unlikely but possible that during your trip in Asia when you “picked up 4 these tubes for less than $50” you just was given the set of garbage tubes. Some people who use a lot of tubes trash any faulty one and some of them just put it in separate box and the box got filed up then they sell it as “set of tubes”. It is possible that you got your “winning” lottery ticket. I never do it with tubes and if I have any problematic tube I rather break it glass (to avoid temptations to”fix it”) and trash it. However I did it a lot with compression drivers when I was experimenting with them: the drivers that were un-recoverably dead I combined by pairs and sold in far countries…. So, there are a lot of assholes out there…

The comments that you quoted “10-20% to be significantly out of spec” are correct  but even being significantly out of spec does not mean the they are not operational as the flexibility to set your custom bias for each out of spec tube make them all perfectly usable. I made a LOT of experiments trying to detect if the 6C33C tube that need 45V bias or 120V bias have any difference in sound. After 100Hr of burn and the bias normalizing to let say 57V bias or 80V respectfully I was not able to detect any sonic distinctions. Another thing: do not believe that anybody would sort them out – no one does it. Well, some do, Vladimir Lamm for instance burn the 6C33C for 72Hr, measures them and match then by gain. So, he used to sell his confirmed 6C33C at $80 a tube and it was 10 years ago. I am sure now he sells them for $180. The Lamm’s tube are fine for some kind of mid-west gynecologist who never saw a screwdriver as he can’t not use it in your work but absolutely no necessary for the people who comfortable to measure plate current and tube gain.

There are few types of 6C33C tubes out there. The Ulyanov tubes are the most common and perhaps 95% of them are made in Ulyanov. There are productions from other plant and by other vintages but they are no better from the perspective of reliability or stability of parameter then Ulyanov. Again if you have full bais control then you shall not have any problems with reliability and stability of 6C33C. Let presume that your “lucky” buy of 6C33C in Asia was just an accident. Hey, I promise you that it was not the last $50 you have lost in audio….

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
09-18-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-19-2010

Post #: 23
Post ID: 17024
Reply to: 17011
It's the tube
fiogf49gjkf0d
Romy,
I have good confidence that it was the tubes and not the circuit. I have checked the cathode driver that bias the 6C33C and there was not any problem. Sure if the cathode bias failed, the 6C33C current will shoot way up and burned up the fuse, it did not happen in this case. The 6C33C tube went with a small pop, such as you cue the cartridge onto a record, it did not die, but the bias current is way low. I have a total of 8 tubes, after burning in the heater for a day and test the rest of the tubes, now I have only 4 that bias is within 10V of each other. The other 3 is about 30V off, and one did not have conitnuity on 1 filament.  Like you said, I probably bought some garbage tubes.

I just order some 6C33C tubes on Ebay: [Edited: link removed.]
because these looked interesting with gold grid wire, none of my 8 tubes I had it. I will test these as soon as I receive them.So far nothing was damaged except the tubes, that is good news. I remember reading somewhere that other tubes like 6AS7 sometimes short the plates, one time at the show, I was listening to an OTL that has about a dozen of these 6AS7 tubes, and one of them sparked with a flash and make a very loud noise on the speaker, I hope the same thing does not happen with the 6C33C in the future.

Anybody out there felt that there is one brand of 6C33C better than other? What about the Svetlana?
09-18-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 24
Post ID: 17025
Reply to: 17024
Looking in a darkroom for a black cat which isn't there?
fiogf49gjkf0d

 KOTriode wrote:
Romy,
I have good confidence that it was the tubes and not the circuit. I have checked the cathode driver that bias the 6C33C and there was not any problem. Sure if the cathode bias failed, the 6C33C current will shoot way up and burned up the fuse, it did not happen in this case. The 6C33C tube went with a small pop, such as you cue the cartridge onto a record, it did not die, but the bias current is way low. I have a total of 8 tubes, after burning in the heater for a day and test the rest of the tubes, now I have only 4 that bias is within 10V of each other. The other 3 is about 30V off, and one did not have conitnuity on 1 filament.  Like you said, I probably bought some garbage tubes.I just order some 6C33C tubes on Ebay:

Edited: link removed.

because these looked interesting with gold grid wire, none of my 8 tubes I had it. I will test these as soon as I receive them.So far nothing was damaged except the tubes, that is good news. I remember reading somewhere that other tubes like 6AS7 sometimes short the plates, one time at the show, I was listening to an OTL that has about a dozen of these 6AS7 tubes, and one of them sparked with a flash and make a very loud noise on the speaker, I hope the same thing does not happen with the 6C33C in the future.
Anybody out there felt that there is one brand of 6C33C better than other? What about the Svetlana?

KOTriode,

way I am not the best person who ask about the reliability of 6C33C as I do not acknowledge the reliability problem for this tube.  I have seen this tube failed on OTL applications. I have seen it gone down in PP application as the operational parameters for 6C33C very difficult to match for positive and negative halves. However, I did not see the 6C33C behaved badly in SET applications with output transformer. I did heard the people complain about the reliability of the tube, primary the thermal  run out of plate but I did publish the preventive measures for it. So, what I personally experienced is that the 6C33C with preheated filaments and stable fix bias demonstrate absolutely no problems that you describe. BTW, I use to know a number of 6C33C users and I never hear from them any complains about reliability of your type. Again, the reliability is NOT the same as the values of parameters – they might be anything you can imagine with 6C33C. As I told: since I do not recognize the bias voltage as important operational parameter and can accommodate any voltage with my bas type then I do not particularly care about the parameters run of on the new 6C33C. I care only about plate current and gain and they are dead stable year after year. Below is the picture of my amp with currents right in front of it and they run pretty much dally for a few hours.

6C33C_In_MIlq.JPG

I understand that you do not want to hear my assurances that the tube is reliable if you have problems but since I did not have any problems and do not know the specifics of your circuit then all that I can do is to share my experience. I would tell you even more. I personally, because of some my stupid accident in experiential stags was running the tube at 900mA and 150V for prolong time, dissipating 135W on plate. The tube not only did not go down but I in fact still have this specific tube and the tune is still perfectly operational. If you want more stories then I’ll tell you that I know people in Russia who stupidly believe the 6C33C need to be run at high voltages. Those fools run 6C33C at 650V – twice max permutable for this tube. Reportedly the use it for years and do not complain…

About the different version of 6C33C. I wrote about it in past. I did experiment with many different types of 6C33C but my search was not for reliability (never had problems with that) but for sonic differences. My conclusion is that it was not worthy. I did not see any specific differences between early or late productions, between different manufacturing plans, between different markings, between different “K” marks (Russian equivalent of QA acceptance). They all more of the less were identical in my view. The only reliability problem that I had were the 6C18C – the precursor of the 6C33C. The 6C18C are good sonically but 50% of them I trashed right the way.  But if you read Russian specification for 6C33C then you will see that 6C33C was developed to replace the 6C18C and to eliminate the know mechanical problems with 6C18C assembly.

Regarding the tube that you pointed at eBay with gold plate – I thought that I have all 6C33C ever made in my collection but I never had this one. Russians did make the gold plate 6C33C. The gold plates were made for military and in fact only gold plate tubes were use in Mig’s radar power supply (the regular tubes that we use in audio were not used in Migs). It is VERY hard to find the military gold plate tubes nowadays, no one was able to find them yet as far as I know. It was very limited production and they were reportedly given to air force technicians by signature, like bricks of gold in Fort Knox.  The advantage of the gold plated grid is that they are able to handle full power right from beginning, with no tendency to overheat, as gold-plating reportedly restricts the secondary emission from the grid of the tube. Will it make any difference in Sound? I do not think so but it needed to be tried. The only obvious advantage is that you shell be able to test this tube at full power and full LF right from a freezer… I still would not do it…..

BTW, you need to understand that all my late comments about the sonic quality of 6C33C are made in context of DSET applications. How it would work in context of a full range speakers I do not know. I do not have full range speakers for many years.

The Cat

PS: I took those tubes from Ebay. You said that you have ordered them, so I presume that I did not run the road ahead of you. Let me know if it is OK with you….


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-19-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 25
Post ID: 17027
Reply to: 17025
It will be the 6C33C harakiri
fiogf49gjkf0d
I actually took the remaining dozen of gold grided 6C33C from that eBay guy.  It is hard to say what those tubes might be and it is most likely absolutely not necessary in my case. Still, I figured that to get a dozen of 6C33C for a price of a pair of 2A3 is not bad in the end of the day.

Also, I think that made specifically for air force application they might have some other advantages and the military specification was MUCH less tolerable and much more demanding. To the best of my knowledge there were not 6C33C-BP tubes (BP- military acceptance), so my presumption that gold grid s is a closed to the best 6C33C as one can get.

Now, would it have any sonic difference, particularly in my case – I doubt. Still to get them for the price of a single branch in downtown Boston I think is not a bad idea. I do feel that the eBay guy let them go a bit too cheap. The Morons sell Svetlana 6C33C from 1968 for $60-$80 per tubes. I did buy a few and they were absolutely not distinguishable by operation and sound from any other 6C33C. The Gold Grid 6C33C are 1000 less common then early Svetlana, and the guy sell then for $15 a tube… Well, I am game…

BTW, the funny part is that it is very hard (if even possible) to distinguish the Gold Grid from regular one. I think I will need to take one apart to find the piece with my purchase. This is why I got non-even number – to perfume my own 6C33C harakiri ….

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
09-20-2011 Post does not mapped to Knowledge Tree
KOTriode
Posts 40
Joined on 07-19-2010

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 2,216
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 9,650
Joined on 05-27-2004

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 9,650
Joined on 05-27-2004

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 2,216
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 07-19-2010

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 9,650
Joined on 05-27-2004

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 07-19-2010

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 9,650
Joined on 05-27-2004

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 07-19-2010

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 07-19-2010

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 07-19-2010

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 9,650
Joined on 05-27-2004

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 07-19-2010

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 9,650
Joined on 05-27-2004

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
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