Paul S wrote:

After a few minutes, I checked the amps with a (Fluke 189) DMM, just for drill. Voltage was set down to 175, but current was about 450 mA.  Dialing down the pots, I could not get  the current below 390 mA, even though the pots still turn freely.

Actually when you hit the end it will not turn freely. It will still tune but you will feel that it is wand and that something is flipping inside. With a new 6C33C it is normal to have excessive current what the tube is too fresh. Burn is a bit longer a d the initial rise of current will be stop. I would lower the plate voltage to 130-150V and let the tube to burn at lover currant, let say 300ma that would make 45W plate dissipation. After 10-12 hours your tube in this mode will not push more then let say 230mA. Then set the cruse plate voltage and play only with current. Again, it is normal behavior for this tube. One of the reasons why Lamm I presume charges $1.000.000 per tube that he sells is because he pre-burns his 6C33C – a slightly aged 6C33C has no effect of current rise during start up. BTW, I have written about it before.

What is interesting to note that observed this behavior only with 6C33C in ML2.  Milq with it’s fixed bias has no such an effect. I did not look I not ML2 and I do not know what kind out stage biasing Lamm uses. The plate is regulated for sure but with biasing it is not clear. Since that 6C33C behaves in my amp and in ML2 differently I might presume that ML2 does not use a straight fix biasing. 

Paul S wrote:

So, does anyone know anything about "good" sockets for the ML-2s? I forget when and where I saw some sort of boutique Teflon jobbies that are pretty darned expensive. Maybe DIY Hi-Fi, in Hong Kong? Also, although Teflon is a great di-electric it cold forms pretty readily, too. Does anyone have long-term experience with the Teflon sockets? It is hard for me to picture myself with the ML-2s cracked open and gutted on the project table, with no music until i finally get them sorted out. I suppose if I ever get them open I will also change out the cheaper Electro Cube caps that Lamm had inserted by the time my pair got built. Also, if Onix makes a copper female IEC socket, then i will do that, as well.

Paul, I think you need to be a bit more rational with your desire to update ML2. The ElectroCube 950 caps are a very arguable element that I would consider to update. The stages in ML2 are capacitive-coupled and yes, putting the best caps in there shell be very critical. The ElectroCube 950 are VERY good capacitor and it would be very hard to beat them. You might experiment with some Teflon with copper foil caps of the same volume but you need to do some after break-in testing before within another project. Still, I feel that ElectroCube 950, as good as they are, are perfectly suitable for the amp. The old ML2 has a very good and very delicate balance of everything and I would like not to see people get it ruined. Saying all of it I do admit the facts that it might be better caps out there. ElectroCube 950 sound-wise they are in the same scale as RTX Multicaps. Both are very good capacitors, RTX has a bit more dymick sound but ElectroCubes has a bit more reacher midbass. Still, they are roughly in the same scale of quality of sound.  I do think that it might be something better then they are but the key in it to find “something better” that would offer an improvement in the same direction where you feel the ML2 weakness are. Identify for yourself what you do not like in ML2 and see if the change of your coupling caps would address your dissatisfactions. Any other reason to upgrade any audio element is completely idiotic in my view and shall be discussed on DIYaudio.com forums but not at my site.

Regarding the subject of better sockets. The small tubes have fine sockets and I would not touch them. The 6C33C do use very bad Russian sockets, I have written about the way to deal with it before. You can put the Johnson or Yamamoto sockets – it is very simple procedure.  I would argue that 30K amp shall not have this problem but I think at the time Lamm start to make ML2 the Yamamoto sockets were not around and Johnson is hard to source for production. It is not to mention that ML2 was selling fine with no complaints from customer or reviewers- so why to bother. BTW, I need to note that Lamm does send the regular sockets replacement for free. What my sockets on ML2 got burned Lamm send me free replacement even with no shipping change. For anyone who dealt with Lamm’s “customer service” it shall be shocking news as to learn that Charles Manson would gave blood to save life of his victims.

Also, be advised that the Teflon sockets for 6C33C are not the key. The key is in the design of pin not in the material of the sockets; even Teflon can press the pins to hold the tube more firm.

Paul S wrote:

If Lamm had actually used the larger 950s in my unit I would probably be less curious about it, but for mine he used 10uF 935 couplers with small 950s for bypass (... I assume they are bypass caps...). Hard to imagine 10 uF couplers would not have a substantial effect on the sound. And, like I said, I am curious.

If Lamm used 935 in coupling positions (use 930 in other location of amp is fine) then I would say that repel of them is very desirable. In fact if I did it I would probably do not solder there the hole and did a half-ass job: juts bite the leads to 935 right next to the caps and in the leads that had soldered to the board juts to connect the new caps, sitting then on a few drops of silicon. It shall be 10 minutes task and very simple to do for a person with very rudimental technical ability. I would be VERY interring to know if the replacement of the coupling caps would minimize the sonic issuers I had with ML2. Unfortunately I will not able able to learn if from your experience and I have no my own ML2 anymore….

Paul S wrote:

I keep getting noise from the 12AX7/sockets, and this noise gets resolved when I clean the connectors.

I am sorry,  but I do not believe in it.

Romy, harken back to post #117 in this thread to refresh your memory about the "acceptable" small tube sockets used in this amp. Maybe Lamm used good sockets in your own amps, but the ones he put in my amp are not good. After all, the 12AX7s use the same poor sockets as the 6AK5s, that you had trouble with, yourself...

And yes, why not start with a "quickie" cap swap? I do have a de-soldering iron, after all, so I might even go for the holes from the "wrong" side. And when I look at it this way, not needing to pull the boards, it moves to the list of Things That Will Actually Get Done!

Best regards,
Paul S

Romy the Cat wrote:

Reading at my site Paul’s narrative about his fight with ML2’s tube and the ML2’s tube sockets I need to confess that I always was suspecting that he is some kind of odd wacko with bizarre and sick approach to the subject of amplifier tubing. Too much of what he said just did not make sense to me. Well, until the last night… Disclaimer: (wherever I say ML2 I imply the Lamm ML2.0 version not the ML2.1, about which I do not case) I own two pairs of ML2 that I bought new and used them dally since then. I know dozens of ML2 heavy users who never had any problem with those amps. In fact ML2 were very stable and very secure in operation amps. The Lamm’s ML1, the preamps were with operational “issues” but M1.1 and ML2 were very stable. Anyhow, I have this week a local friend of my brought to me a pair of ML2 and he need a help with inner-amp filter. The amps he brought were not used for a while and were sitting in storage for 5 years. I did the necessary things with filtration and desired to listen them. I have no way to drive Macondo full-range but I have my MiniMe prototype… The plate currant on both of amps was too high. The further inspection showed that ML2 regulators stopped working. The B+ was not eaten by regulator tube and ML2 had 230V at .6A on plate – it is over 130W anode dissipation – bye-bye the 6C33C… Actually, I was rung the 6C33C like this for a whale, when I was searching the problem, the tube did not failed. The ML2 regulator is too simple and cannot work without a load.  Anyhow, chasing the problem in the ML2 belly I was wondering why the regulator was down… on BOTH AMPS. The das tune was on, the error pentode was on the regulator tube was on. The design was very simple and very straight forward… I measured and confirmed that the right voltage was given to all tubes but it looks like the error amps did not corrected the voltage. I test the error amp’s pentode it was perfect. I went to my storage and brought my own WE 6AK5 – the same result. What the hell I was wondering…. I pulled my dummy loads to substitute the output tubes as it was glowing with 130 on plate like crazy and then the regulator … kicked in!!! OK, guess what was the problem? The problem was the fucking frugality of Mr. Vladimir Lamm. This guy makes 30.000 worth amps with none-treated steel tube sockets. It was juts ridicules – the tube sockets on 6AK5 were rusted to the point of no contact with cathodes. The sockets were cleaned and the amps were working flawlessly… I wonder if Lamm would use not $.15 tube sockets but $1.15 then would it lead to extra $10.000 of the retail price… Anyhow, the idiotic economy on such a mall things in a flagman amp that cost $30.000 (the amp was made in end of the 90s with serial number in 40s) appears to me… to idiotic. It is not something that saves money to Vladimir and it is not something that Vladimir do because of his ignorance (his is a brilliant technologist). Those things that he does are because his attitude and he learned that his customers and his revisers are deaf idiots and he can go away with it. if not then how can in such case one explain that in early prod action of ML2 Lamm used Cube 950 caps for inner-stage coupling – the phenomenal-sounding Polypropylene foil caps. In the amp that I was fighting with regulator all coupling was made by bypassed Cube 935 that are Metallized Polypropylene and with very different, less sophisticated sound. It was $7.35 for Cube 950 vs. $5.11 for Cube 935 – I am sure it was well worth it… I was wondering how much Lamm “saved” in more important thing – on output transformer for instance. I wonder how far Lamm electronics sound off from the level as it MIGHT sound if the electronics was made with respect. I remember a few years ago Lars Fredell let me to listen his M1.1 that Lamm custom-made (just with better parts) for him. It was WAY more interning then the production M1.1. Well, I presume that if Lamm wish to kiss somebody else ass with sound then his is perfectly able to get better sound of his design. I wonder why it shell be a condition? Does Lamm’s series production is just the Lamm’s attempt to eagerly spit on somebody ass? Well, if you understand what I mean then you understand what motivated me to design Melquiades and do not be subordinate of that “subordination”. Anyhow, the Paul’s suffering with tube sockets was understood now, at least… The caT

Paul S wrote:

A year (and a pair of V2s) goes by like nothing. I just changed V2 tubes again, and this time I dialed the current way down before I fired up the amps, per instructions. After a few minutes, I checked the amps with a (Fluke 189) DMM, just for drill. Voltage was set down to 175, but current was about 450 mA.  Dialing down the pots, I could not get  the current below 390 mA, even though the pots still turn freely. How good are these pots?  Do they actually have "stops", where they won't turn any further?  Again, I ask because it seems like I've come to the end of their electrical adjustment (current will not drop any lower with further turning), even though it is still quite easy to turn the pots with a tiny screwdriver.  FWIW, I am pretty good with tools and I have a pretty sensitive touch, so it's not like I roughed them up, or anything. This is the third pair of V2s I've put in these amps.  This is the first time I've encountered this situation; but then, I've never taken measurements so soon after start-up, either. Paul S

Laurent,

The V2 in 6C33C does NOT need to be matched by other characteristic then gain and it is very easy to do. If you have two V2 tubes and they have different entry points for bias but the same gains then you will not detect any sonic consequences – it was tested many times by me.

About your first problem would be more complicated to tell from distance. The ML2 has a regular voltage regulator based upon a voltage reference tube, pentode amplifier and the 6C33C that serves as regulator (V1). There are many different versions of voltage regulators that sometimes they are called Error Amplifiers. I do not know what Lamm implemented in there but ALL regulators are VERY simple and it hardly anything might be broken in them. Make sure that the gas tube went off and that is has the reference voltage on it. Make sure that the reference voltage from the gas tube is delivered to the amplifier cathode. Make sure that the voltage from amplifier plate goes to the regulator grid. Replace all 3 tubes and checked above. If Lamm used a shunt regulators (that is possible if you have LOVER voltage) then anode of all 3 tube are combined with juts a control amp having a plate resistor and it would be even more easy to debug. I still feel that nothing shell be wrong with your amp as there is nothing in there to fail. Check the contact on the tube sockets…

BTW, if I had ML2 I would try to use it with no regulation of V2 plate at all by disconnecting the regulator. I am NOT saying that it would be better – I do not know. And what I have my ML2 I did not try. I was trying to run 6C33C from my .5A Fluke tube regulator with 3 paralleled 807 triodes as regulators and I did not like how the 6C33C sounded. The 3 paralleled 807 gave the same or even lover output impedance as one 6C33C still with 6C33C it might be different. It is not to mention that different regulators do sound differently. I just afraid that with no regulation ML2 would need to have different PS as it’s ripple and current stabilization characteristics would not be optimum. Anyhow, I do not reinvent the ML2, it is what it is and probably to try it without regulator is not a good idea.

Paul S wrote:

Aparently, a few people complained back to Ken Chait that his "carefully-matched" (with an adaptor on his Amplitrex AT-1000 machine, i presume) pairs either weren't matched to begin with, or they did not stay matched.  Anyway, Ken's response was that he will no longer knowingly sell 6C33Cs to "Lamm owners".

First of all I do not know who Ken Chait is. I presume that he is a tube dealer who sells 6C33C. Hey, how frequently you see me to defend the dealers? In this case I would. I think that was incorrect to bitch about Lamm owners as they are not particularly annoying breed. The 6C33C before matching need to be well burled, I would say 60 hours at least - NO ONE would do it. Since Ken Chait charges probably just a few bucks for matching then I assure you that he does not burn the tubes. To match the “fresh” 6C33C is like building a levee from sand. So, why I am defending the Ken Chait? Because even the well burned and match 6C33C very much might age with different tempo, in fact they will age differently – this is the nature of the 6C33C beast. You are annoyed? Wait when you run DSET with 6C33C – then you will be really annoyed.

Anyhow, the problem is not with Ken Chait or Lamm owners but in the totally foolish expectations that 6C33C might be matched. Well, if you do burn the 6C33C for 50-60hours and do match it by gain, by bias and by currant then you have MORE chance then the tube will age similarly but it will NOT be an assurance. Do you know how many tubes I would need to go over to match the paid of 6C33C properly? I would say 20 tubes. So, I feel that the best solution would be juts to buy a shit-loaded of cheap 6C33C. Match them by gain and discard bias. That is fixed bias, what would be the difference is you get you default current with 70V or grid or 80V.

What I do is to use a pair of new tubes, match them by gain, check the gain each few month and in one year I trash both tubs if the tubes did not develop any other “problematic” signs earlier.

Romy the Cat wrote:

Anyhow, the problem is not with Ken Chait or Lamm owners but in the totally foolish expectations that 6C33C might be matched. Well, if you do burn the 6C33C for 50-60hours and do match it by gain, by bias and by currant then you have MORE chance then the tube will age similarly but it will NOT be an assurance. Do you know how many tubes I would need to go over to match the paid of 6C33C properly? I would say 20 tubes. So, I feel that the best solution would be juts to buy a shit-loaded of cheap 6C33C. Match them by gain and discard bias. That is fixed bias, what would be the difference is you get you default current with 70V or grid or 80V. What I do is to use a pair of new tubes, match them by gain, check the gain each few month and in one year I trash both tubs if the tubes did not develop any other “problematic” signs earlier. The Cat