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In the Forum: Audio Discussions
In the Thread: Initial thoughts about new/old Lamm ML2s

Post Subject: Some ML2 & 6C33C ramblingsPosted by jessie.dazzle on: 12/7/2009

Potentiometers:

Paul S wrote:
"...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..."

These potentiometers are protected by clutches at both ends of the adjustment range; they will "freewheel" if the range is over-run. In other words, turning them too far will not destroy them. They are designed to emit an audible click (at both ends) to let you know they've reached the end of their adjustment range.

6C33C Bias:

Romy wrote:
"...The 6C33C before matching need to be well burned, I would say 60 hours at least - NO ONE would do it..."

I've found it necessary to monitor replaced V2 tubes closely; 4 months into it and this last pair is still not as stable as the pair I removed. Lamm documentation warns that letting them drift past the indicated 0.31 VDC will shorten the life of the tube, and that 0.31 is in fact a max figure (at which point they are already being run hard).

I've noticed that I almost never have to re-adjust the V1 potentiometer; bringing the V2 tube into spec will result in exactly the correct V1 reading.

Btw, anyone using Lamm L1 or L2 preamps may want to download instructions for setting voltage when replacing the regulator tube. Instructions available from the Lamm site.

6C33C; Date of manufacture:

LX wrote:
"...I have just realized that they date as far back as January 2005!..."

No reason to get excited; this is just the date of manufacture. Since you live in France, you might consider finding a good Metrix U61 tube tester, then make the correct adapter for the 6C33C...

How I clean the pins of the 6C33C:
(sounds crude, but if done with care it works great)

Buy a good quality pair of small electrician's combination or "linesman's" pliers like this
http://www.toolstation.com/images/library/stock/webbig/68981.jpg
(the entire tool should be shorter than the length of your hand, teeth should line up, and there should be no play in the pivot)

Holding pliers perpendicular to the tube's pins (small teeth in jaws parallel to the pins), gently clamp one pin, making sure it is completely seated in the valley BETWEEN the peaks of the little teeth in the jaws of the pliers. You'll have to rely on your touch to modulate clamping pressure, but keep it light; it will come naturally to anyone who works with his hands... If unsure practice on an old 6C33C; the idea is to go only slightly beyond merely contacting the surface of the pin.

While maintaining this light clamping pressure, slowly rotate the tube and pliers in directions opposite to each other until blocked by the neighboring pin. Move on to next pin and repeat.

To reach the small areas where the pliers will not go (the final few degrees of rotation will be blocked by other pins) brush lightly with the edge of a 3M Scotch Brite pad.
http://www.3mselect.co.uk/images/product/large/1168.jpg

Blow off debris and install tube.

Done.

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