One ironic thing about the ML2s is the contrast between the fantastic workmanship and the mostly average parts. Of course, the sockets are plain crappy, and I suffered plenty with them until I started using the dielectric grease. I have been too lazy to replace the sockets or the caps in mine, which are obviously the originals. And anyone looking at anything I ever put in there will be able to tell immediately that my work is not the original...

The absence of a schematic makes even the prospect of working on this thing scary. That big oiler in there looks downright dangerous!

I've said it before and I'll say it again, I'd love to have the ML2 schematic.

Best regards,
Paul S

Paul S wrote:

One ironic thing about the ML2s is the contrast between the fantastic workmanship and the mostly average parts.

jessie.dazzle wrote:

Scrolling down to the images of the Lamm ML2.2, I see something that intrigues me... Four ML2.2s are used to bi-amp the Verity Audio speakers; I didn't know they could be daisy chained by using both the XLR and RCA inputs of one pair of ML2.2s (front pair in this case) to output an unamplified signal to a second pair.

I am not sure what makes you intrigued. This is very typical unfortunate/fortunate configuration for Lamm ML2 bi-amping. The XLR and RCA jacks in ML2 are parallel and they run like built-in Y-adaptor. If you have amp very far from your preamp and do not want to run another long ran cable then you might source your frequency section right from LM2’s input. The unfortunate part is that if you still intend to run a dedicated cable to your let say LF section and if you use Lamm preamp then you can’t/ This is one of the most Moronic thing Lamm did. I did pointed it out to him even what we were close but his discarded presuming that his users are anyhow idiots who does not mater do not understand what they do. He was right about it BTW. So, the Moronic think was that his preamps (L1 and L2, I do not know how about L3 but I think it will have it as well) have single ended and XLR outputs and fully balance topology. So, when you flip the absolute phase on Lamm preamp then your XLR output and RCA out become in opposite phase. Pretend how fun it become to bi-amping but as Vladimir very acutetly noted his customers are to idiotic to understand it. Go read all reviews ever were written about L1 and L2 and see if any of those Morons ever noted it.

jessie.dazzle wrote:

Also, I'm curious about that black thing that looks like a tube shield...

This is not tube shield but a capacitor installed trough the amp chassis, similar to what I did in the earlsy version of Super Melquiades

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=1207

What is interesting is that to use this “trough chassis” configuration was absolutely not necessary. There is plenty space at the bottom of the amp to locate a larger snap in cap and there are wide and short configuration of any large caps if the high become a problems. There is certainly nothing wrong in making this trough chassis connection but I think Lamm just wanted to emphasize that his new amp is different from his old versions. I think there is no “claimed” change in input stage in there but most likely the B+ for input stage has a local cap to shunt B+ right next to the 12AX7 anode - the way how it shall be. If that is the” great Lamm improvement” then Lamm is of course is very “unique” engineer.  BTW, I do not have doubts that in context of this compromised PC board assembly of ML2 the move of PS cap closer to load shall be beneficial.

I finally received and installed the new tube sockets for the 6C33Cs. Results: NICE!!!! Rock-steady plate current and voltage. The sockets I used have a solid machined Teflon base with receptacles that each have multiple contacts for the pins.

jessie.dazzle wrote:

Before changing the sockets the sound had gradually picked up some glare (old sockets were probably micro-arcing like hell); the new sockets fixed that and, in the time I've owned them these amps have never sounded better (I'm the second owner). The sound now is now generally more relaxed and natural. I do not attribute the improvement so much to the Teflon, but rather to the pin receptacles and of course to finally being able to properly set the bias; for the past six months (prior to socket replacement) I had been running it at about half the recommended settings in order to keep things from going overboard during drift. With the new sockets, I have not tried listening with the bias turned down to half the recommended setting, but I should, as it would give me a feel for how much this factor alone might be contributing; however, in the past, varying operating points never seemed to make a difference of this magnitude. The sockets did require some serious modification work before they could be installed; I took some close up photos showing the process; I'll post them if anyone is interested (I might not get to it instantly, as I'm neck deep in other stuff).

I did not use those sockets for 6C33C. I use Johnson sockets, love them and never had any problem with them for 6 years as I started to use them. I use the expensive Teflon sockets for my driver tuber and they are very good. Interesting is the material of sockets is very much irrelevant; the configuration of the pin grabbing contacts is the key. I do not know how the contacts are made in the Teflon sockets. For the small currents Teflon is very good as it stress the contacts to be very tight. For the tubes like 6C33C the Teflon that would push the contact to be tight is not good idea as the coals run much hotter and if they are surrounded with Teflon then they would not be ventilated well. Still, I did not play with them and do not know how they made. BTW, there is gay out there who looks like do not like them

http://www.troelsgravesen.dk/AudioMirror-6C33.htm

jessie.dazzle wrote:

One did; in reviewing the L2 preamp, John Atkinson (Stereophile) wrote: "...The absolute polarity was preserved from both sets of outputs with the front-panel switch set to "0 degrees," confirming that the XLR jacks are wired with pin 2 hot. Setting the polarity switch to "180 degrees" inverted the unbalanced output but not the balanced output..." From the manufacturing point of view there may be a good reason why this is the case, but from the consumer's point of view, it is not ideal.

Good one. I do not remember it. Still from the Atkinson language I see that it was written by Atkinson in his technical summary not in the review itself. In his technical measurement summary he just report data but not interprets data. So, users of L2 do not understand what it means. At the time when I used L2 I spoke with many L2 owner including with a few people who bi-amp. No one let me say again: NO ONE, including those who consider themselves the heavy L2 users realized that XLR jacks do not reverse phase. This type of setting is absolutely not permitted in a balanced preamplifier. Mind you that inverting phase is one of the main functions of this preamp as it is made with fully balanced topology; this is why is double all parts of the signal circuit.

jessie.dazzle wrote:

The part that grips the pin is made of several tiny contacts. I don't think they are gold-plated; in any case, gold would likely not fare too well in the presence of the heat generated by the 6C33C. Image below: In the case of the Teflon sockets for the 6C33C, the Teflon plays no roll in clamping the pin; there is in fact a generous gap around the pin receptacle and all clamping force comes from the springiness of the metal contacts, which are confined by a hollow cylinder. Next two images: The pin receptacles are composed of threaded parts, which, in my opinion, should be soldered as one to improve both electrical and thermal conductivity between the individual parts, as well as keeping them from coming loose over time. Image below: Here is the problem with these sockets... The threads of the large pin are not long enough (not enough of them protrude through the Teflon base) to allow proper threading of the securing nut. Threads on the smaller pins are longer and the smaller assemblies can be adjusted to compensate, but as this is not an option with the large pin; thickness of the Teflon base must therefore be reduced by at least 1.5mm. Image below: Showing material that needs to be removed to allow for short threads of large pin. Image below: Fully assembled after Teflon base has been reduced by 1.5mm; note, even after reduction in thickness of base, there are still no excess threads protruding past the securing nuts. In the case of the ML2, the four chassis mounting holes in the Teflon base must also be enlarged. Image below: New sockets have pin receptacles closer to the center of the socket... Lamm rightly leaves no excess length, so getting the original wires to reach the pin receptacles is tricky. In spite of the work necessary to correct the thickness issue, I'm very happy with the results and would in fact recommend these sockets. I do nevertheless have to admit, considering the price paid (something like $38 each plus shipping and customs), that it is reasonable to expect a finished product. I assume these are among the first that the manufacturer has produced for the 6C33C, as the thickness issue could be easily corrected during future production.

Very good job with the sockets. I did not see this type of the sockets you use. The only one Teflon sockets for this tube that I seen were $100 sockets by a Japanese guy, I think it was Yamamoto or something phonetically similar. They were a bit different; I like your better as they have better pin ventilation. Ideally I would like to have more air exposure to the 6C33C pins and the pin on this tube run very hot. I would like to have a micro heat sink on the pins to let them to be cool down. Two words of warning: make sure that you wind the wire around the pins and then fill it with plumbum. The old sockets had whole where the wires were able to be inserted and tighten before soldered. Another thing: do not use the low temperature soldering metal. Many of contemporary soldering metals have silver in them that lower the melting temperature. If you solder with this easy to use soldering metal then the temperature of the socket pit will eventually melt the join. I had a few times until I learn how it needs to be done properly.

 I have one question to ask. From what I see you changed the wire that goes to filament. Lamm has Brown-Brown/White cable but you have has White-Brown/White. Was any reason why you changed the wire?

jessie.dazzle wrote:

No, I did not change the wires, just took the photo of the old socket from a different angle (off 90°); you need to mentally rotate the image.

jessie.dazzle wrote:

Yes, in a way you are correct; the wire is white but over time became sort of brown toward the socket; this is either from the metal contacts of the socket having oxidized in close proximity to the insulation, or simply from the light colored insulation having been close to the heat... I cleaned the insulation using acetone, which restored the white color.