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  »  New  The short "6C33C Survival Guide"...  Ac filament.....  Melquiades Amplifier  Forum     20  373403  12-18-2007
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10-03-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 121
Post ID: 8440
Reply to: 8438
When Cooler Heads Prevail
Romy, it sure sounds like you were right when you said that at any given point the ML2 was a work in progress.

The .033 uF 950s in my amps are indeed 1000V; maybe L got a quantity discount; maybe they're 2nds; who knows at this point why they have such a high rating.  But it does look like L went from 2 uF to 10 uF for the 400V couplers, 2 per amp.  Is this 1 for each tube half of one stage, or one for each of the first two stages?  Maybe he upped the C because he wanted to drop the R value???  Still, that's quite a jump...

As for the really BIG, single, unlabled "industrial" oiler(?) I mentioned, I would guess it was for the output RC, but there are so many wires hooked up to it...   I could not/didn't really try to see if the thing went to the OPT.

Regardless, you are right about leaving stuff alone every chance I get, of course.  And AFAIK at this point my "amp problems" are the bad electricity rather than the "wrong" caps, etc.

It is supposed to cool off around here starting tomorrow.  Like I said before, one good listening session would probably cool my jets, except for the 400V 935s, which I am simply too curious about to leave alone indefinitely. Although I am not sure I'd go for a handful of 950s instead, the giant double-wound exotics don't seem likely here, either.

Best regards,
Paul S
10-14-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 122
Post ID: 8510
Reply to: 8440
Then, out of Nowhere...
fiogf49gjkf0d
Wifey went on an errand today and on a hunch I fired up the system to listen to some Schubert lieder and a piano sonata.

Despite a dry east wind, it was not as hot as predicted, and despite schools in session, etc., the electricity was very good.  I should mention that I also had the system on for a few hours last Saurday.

Well, I had my reference back, at least for a short session, and it is quite satisfying, within the planned/accepted limitations.  Voice and piano at live level are clear and very nice in terms of attack, dynamics, pitch, tone and timbre, details, etc.; all good.

Did someone mention swapping out capacitors?

Why would anyone want to do that???

I can't say for sure (because maybe it's just the better electricity), but "stand-by" warm-up may be +/- a waste of time.  Anyway, today I went promptly to soft music and then raised the volume over a 20 minute period, until it was quite loud, with better-than-usual results, and certainly a lot less waiting than usual for the amps to "clear out".

Paul S
03-07-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 123
Post ID: 9962
Reply to: 8510
Another Day, Another Annoying First...
fiogf49gjkf0d
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
03-08-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 124
Post ID: 9964
Reply to: 9962
The Lamm ML2 biasing.
fiogf49gjkf0d

 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. 

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
03-08-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 125
Post ID: 9970
Reply to: 9964
Suggesting the Ladder
fiogf49gjkf0d
Thanks again, Romy.  The bias pots, mechanically, are just as you observe.

I supposed that the extra current draw during burn-in was normal for the ML2s but I had not noticed it before, since I typically do not bother to check or try to set bias until an amp's innards are warmed up and +/- stabilized.  At the same time, the uniqueness of the situation and the vague action of the pots combined to give me some pause; hence the post.

I guess good Followers, who do as they are Told and Buy Everything from Lamm Industries, would have no need to know any of this, since it now appears that Lamm's goals for Total-In-House-Control include keeping amp-specific info to ensure Consciousness-Free-Substitution of V2 tubes.

Is this careful stewardship or a Presunmption of Moronity; or is this what it looks like, namely an Open Attempt to keep a Revenue Stream at the expense of an ill-informed (and presumably-docile) clientele?  While the case of the V2 tube could be perceived as either of the the former options, the way L treats and describes the other tubes (especially the 6N6Ps...), along with a general dearth of information or communication concerning actual amp useage, seems to suggest the latter.

Best regards,
Paul S
11-01-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 126
Post ID: 12114
Reply to: 9970
Maintenance and the Life of Parts
fiogf49gjkf0d
Romy's recent post on the trials of 12-channel DSET hi-fi made me feel a little better, but his point about maintaining performance is well taken, none the less. One simply must have an aural reference and some rigorous methods for keeping things sonically up to snuff.

It has been obvious to me for some time that the clock was ticking on the cheap-o tube sockets Lamm installed in his "ultimate" amps. In fact, the alarm went off some time back, and my subsequent "remediation" with dielectric grease was actually too late, realistically speaking. Although it did lower the paper-y sound of micro-arcing, it has not eliminated it, and it has been a matter of laziness on my part rather than satisfaction with the grease in this case that has gotten me this far with the same old crappy sockets.

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.

Otherwise, the amps seem to be solid, and certainly the workmanship - whether Lamm's or some carefully-chosen jobber's - is the best I have ever seen.

Sigh...

Paul S
11-01-2009 Post does not mapped to Knowledge Tree
scooter
Posts 161
Joined on 07-17-2008

Post #: 127
Post ID: 12116
Reply to: 12114
Teflon sockets
fiogf49gjkf0d
Here's a start on teflon sockets I had bookmarked for some reason:  

http://www.diyhifisupply.com/?q=catalog/46/vacuum_tube_sockets
11-02-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 128
Post ID: 12118
Reply to: 12114
About the Lamm ML2 updates.
fiogf49gjkf0d

 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.

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
11-02-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 129
Post ID: 12119
Reply to: 12118
If Only
fiogf49gjkf0d
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.

As far as the 9-pin sockets, I keep getting noise from the 12AX7/sockets, and this noise gets resolved when I clean the connectors.

As far as sockets in general are concerned, I don't like even the idea of steel contact points. I am more interested in copper contacts than the Teflon. I absolutely do not regard Teflon as a silver bullet, and it is not the Teflon I am shopping for. But, try to find gold-sputtered copper pin holders that are not part of a boutique "Teflon" tube socket...

As far as addressing the ML2 weaknesses, I would be very pleased and also quite surprised if any cap swap made the ML2's "self-limiting" go away. This I would have to rate as a considerable bonus.

At this point, a cap swap would be more of an exploratory move, just because i had the case opened and the boards out, to see how the sound is changed.


Best regards,
Paul S
11-02-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 130
Post ID: 12121
Reply to: 12119
The recappication of ML2
fiogf49gjkf0d

 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.

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
11-02-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 131
Post ID: 12122
Reply to: 12121
Post #117 Re-visited
fiogf49gjkf0d

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

11-02-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 132
Post ID: 12123
Reply to: 12122
..."keep getting noise from sockets..." not way.
fiogf49gjkf0d
Paul,

I do not remember I had problems with 6AK5 sockets, and frankly I feel that your preoccupation with small socks of ML2 is a bit strange.  If you “keep getting noise from the 12AX7/sockets, and this noise gets resolved when you clean the connectors” then something is very wrong and then problem not the sockets. If you feel that the sockets are the problem then just use wider sockets saver, still I would not believe that it is possible. They are all low current/voltage tubes and those sockets might not have contact but they will not create any noise that might be fixed by “cleaning” them.

The Cube 935 in coupling positions need to be replaced no questions. It is shame the Lamm used metalized plastic caps in $30K amp…

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
11-02-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 133
Post ID: 12124
Reply to: 8377
Memory Fades Like the Afternoon Sun...
fiogf49gjkf0d
 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


Not that I need or expect concessions...

Paul S
11-02-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 134
Post ID: 12125
Reply to: 12124
Contact vs. Noise
fiogf49gjkf0d
Well, it looks like it was what I had but until you reminded it I did not recall. The key is that it was not with my amps bur with the amps of my local guy. You see, his amps were sitting for a long time and the sockets wend bad, rusty. In your case you use the amps dally and sine you clean the sockets one and then keep the amp in your home then the sockets shall not go bad.

You still are missing however point what I do not believe.  If your socket is failed then socket has no contact or bad contact to one of several tube pins, the way how it was in my example above. However, you do not report that you have no contact but you say that you “keep getting noise from the 12AX7/sockets, and this noise gets resolved when you clean the connectors”. I do not know any NOISE that might derive from bad sockets contact, particularly in the case of ML2. In ML2 the 12AX7 ran both half in parallel, so it is very unlikely you might have any problems with contacts and I personally know no circumstances under which a bas contact would cause any noise for a line-level signal.

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
12-05-2009 Post does not mapped to Knowledge Tree
Lx_
France
Posts 33
Joined on 12-05-2009

Post #: 135
Post ID: 12423
Reply to: 9962
Symptoms of a V1 tube dying?
fiogf49gjkf0d
 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

Paul,

Thank you for this feedback. I do kind of have the reverse problem: I cannot get the plate voltage higher than 169V, no matter how up I dial the pot (BTW, mine does not seem to have stops, though it is on a ML2.1). Then the amp failed, I suspect the internal fuse blew as it did a few days ago. I replaced it today, the amp then worked for around 10 minutes before this failure. Except this time I kept an eye on the Fluke and noticed I was unable to set plate voltage as should be. Is this a sign of the V1 tube dying (might as well say dead)?

For info, I bought those amps used almost a year ago. I have changed the 6N6Ps twice already (every 6 months), but other tubes are probably the original ones. I have just realized that they date as far back as January 2005! It would be no surprise that a 6C33C failed. In that case, from what I have been reading here, V2s are probably sonically dead as well (note to self: do yourself a favor and change V2s once a year at least).

I would love to be able to buy 6C33Cs in bulk and match them by gain as required for the ML2(.1), though I lack the methodology to do so, which is too bad as it surely is quite easy to do. Are you still getting your V2s from Ken Chait?

Regards,
Laurent
12-05-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 136
Post ID: 12424
Reply to: 12423
The Lamm’s ML2 regulator.
fiogf49gjkf0d

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.

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
12-05-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 137
Post ID: 12425
Reply to: 12423
Game, Set, Match
fiogf49gjkf0d
Laurent

Although I have whined that the ML2 requires "tweaking" to get its best, the truth is that it is closer to the dream of acceptable "plug and play" performance than any amp I have ever used.  Which is a long preamble to saying I am hardly an expert when it comes to the electrical doings in this amp, mainly because I have not had to be, and I am too lazy and nowhere near interested enough in DIY to dig into the things until I want to accomplish something specific.

If you have a manual, it is actually pretty informative, as these things go.

V1 is a voltage regulator, so no surprise that it's death affects voltage (and current...).  OTOH, a dying V2 might display similar behavior.

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".

I'm not saying you shouldn't stock up on 6C33Cs, but the tubes you are most likely to burn through are the 6N6Ps.

I also wonder about the supposedly simple but ever mysterious procedure for matching 6C33Cs for gain.  Presently, my amps are ~ 2 dB apart.

Best regards,
Paul S
12-05-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 138
Post ID: 12426
Reply to: 12425
Ken Chait and the “annoying” Lamm owners
fiogf49gjkf0d

 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.

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
12-07-2009 Post does not mapped to Knowledge Tree
Lx_
France
Posts 33
Joined on 12-05-2009

Post #: 139
Post ID: 12434
Reply to: 12424
I don't know what happened
fiogf49gjkf0d
Romy and Paul,

Thank you for your help and comments. I decided to move the amp on the floor and on its side so as to be able to monitor it during operation. As it had worked for 10 minutes after replacing the fuse, I was confident nothing should be damaged inside (well, to be honest, I didn't exclude a nasty fault, but it seemed less likely and I didn't want that to be). I was suspecting a problem with the regulation stage, because I could not raise plate voltage higher than 169V just before the second failure. I replaced the 3 corresponding tubes with the ones from the working amp, changed the fuse (which had indeed blown again). Then I switched the amp on, closely monitoring plate voltage and current. This time I was able to adjust to 175V as required. I also checked voltages as suggested by Romy: VR tube voltage (BTW: I have 84.5V or 84.7V for the two 5651s, though they are rated for 85.5V), which is indeed applied to the cathode of the 6AK5 (error pentode), and 6AK5 plate to V1 grid. Everything was in order.

After 40 minutes without a problem, I decided to put back the original 5651 and 6AK5. I thought the 5651 reference voltage might be too low or the error amplifier tube was unable to apply sufficient correction. But after another 40 minutes of flawless operation I knew I was on the wrong track.

At that stage I was suspecting a faulty 6C33C being unable to regulate correctly, which would make the error amplifier work beyond its operating range, thus leading to the fuse blowing. Note that those are just my guesses as I don't have the schematics and don't know where the fuse actually is in the circuit. Also, the V1 tube on the failing amp has a less shiny getter than all 3 other 6C33Cs.

So I put back the original V1 tube. Now all tubes were the original ones, so I was in the configuration that led to the two previous failures.

But the amp worked perfectly for the next 10 hours. That was yesterday. And it has worked just as well for the last 2.5 hours. I have no idea what can explain the difference in behavior.

One thing I have noticed is that the location of the fuse on the PCB is labeled 1.25A (see here). But the fuse that was there was a 1A, and I replaced it with similar ones. Is it possible that the missing .25A is just enough to sometimes make the fuse blow when it should not?

Anyway I will order two full sets of new tubes from Lamm, because mine are probably quite worn out by now. Especially the 6C33Cs. I have plenty of 6N6Ps, so those are not a problem (but I cannot tell Lamm not to give me those). As for other tubes I will put on the new ones when they arrive and keep the current ones as spares.

In the meantime I will be praying that the amp keeps working.
12-07-2009 Post does not mapped to Knowledge Tree
Lx_
France
Posts 33
Joined on 12-05-2009

Post #: 140
Post ID: 12435
Reply to: 12426
Are they that bad (well, sort of)?
fiogf49gjkf0d
 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

Well that is interesting. I knew from other posts of yours in various threads on this site that the characteristics of the 6C33C vary a lot from on to the other and that you cannot expect that any given pair will be identical enough to be used as is as V2 tubes. I also remember that you said matching them by gain is enough (I assume that is because plate voltage and current can be adjusted). But learning that they may also age quite differently is another matter, and not quite reassuring.

If that's the case, I must be lucky because I don't hear that my two amps have different gain. They are surely not equal, but for practical purposes they seem so to me (probably within 0.5dB). Of course this is just me and I don't claim to make a statistical rule from a batch of 2.
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