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01-10-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 151
Post ID: 12660
Reply to: 12438
Cycling bias
fiogf49gjkf0d
Since renewing all tubes in both ML2s, over the period of about 3-5 minutes, the V2 bias on one of the amps cylcles between .27 and .33VDC. Is this behavior indicitive of a defective 6C33C?

jd*


How to short-circuit evolution: Enshrine mediocrity.
01-10-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 152
Post ID: 12661
Reply to: 12658
The General Electric 12AX7 tubes
fiogf49gjkf0d

 miab wrote:
I'm about to place an order for some 12AX7 tubes. The GA 12ax7 tube you mention doesn't seem to come up in my search. Is there other info regarding this tube?

I am not sure but it is possible that General Electric never made tubes after 50s. The tubes that I had were GE but it I possible that they were just rebranded. Sylvania, RCA, Raytheon and few other made tube in US, the GE, Westinghouse and many other just re-brand them.  Anyhow, the GE that I got came with very first ML2 that I bought. After many tubes I tried I replaced them with better German tubes. The second pair ML2 that I bough cams with RCA 12AX7 – I did not like them at all.  I was running the MF ML2 with selection among smooth better plate Telefunken (they are all different – party by party) and bass ML2 with ribbed plate Telefunken. That was the best configuration I was able to get from a quad of ML2s.

I remember that among all 12AX7 contestants the ordinals pair of GE 12AX7 were at very top of the list of the tube I like with my MF ML2. They were no flashy and exiting as the best European tubes but they were very nicely balanced. I bought a few more of them intending to try them in my phonostage but I went with other tube in there.
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
01-10-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 153
Post ID: 12662
Reply to: 12660
The cycleing bias?
fiogf49gjkf0d
 jessie.dazzle wrote:
Since renewing all tubes in both ML2s, over the period of about 3-5 minutes, the V2 bias on one of the amps cylcles between .27 and .33VDC. Is this behavior indicitive of a defective 6C33C?
That is not good. Try to shake the tube in the socket and see if the cycleling is corresponding in any way with shaking – it might be burned out socket where the arked spot on the socket does not work very well with the pink of THIS tubes (Paul do not start!). Check in the voltage from the regulator (175) is stable on another (old) tube.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-10-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 154
Post ID: 12664
Reply to: 12662
Drift, Flux and Tubular Logic
fiogf49gjkf0d
Jessie, since I got my amps I have followed Romy's suggestion and recycled swapped-out V2s into V1 service. As it happens, I do not run V2s (or V1s) over a year, but I have had no problems of any kind that I can relate to following the annual V2-to-V1 transfer practice.  OTOH, I have never had the problem that you describe, either.  I think I paid about $55USD for the current pair of very nice (so far) old Svetlana 6C33Cs I now have in V2 position, but no matter how much I'd paid I would not hesitate to swap out a pair of V2 tubes if one was acting up.  First try swapping the V1, and if that doesn't solve the problem, go through the ritual of breaking in a new pair of V2s, as well.  But be persistent and systematic, both.  I can't tell you how many times over the years I have had ongoing problems either because of multiple, apparently unrelated tube failures at once or due to failures of two (or more!) candidates for the same duty in succession, up to three clinkers in a row!  Who would suspect such multiple failures?  But you have to be ready and allow for it, or situations like this can drive you nuts!  BTW, I have had OK results cleaning tube socket contacts with commercial grade "no residue" contact cleaner and those little, long, round "interdental" brushes that some wack-os (apparently) actually use between their teeth. And just to remind, I have had somewhere between zero and very few problems with the micro-shorts since I started using a little ignition-grade dielectric grease on pre-cleaned tube socket/pin contacts.

Regarding the GE input tubes: I think I spelled out more about the old GE input tubes a ways back, up this thread.  The written designations have long since rubbed off my tubes, and now all I remember (I think...) is that they are among the earliest 5751s, older than dirt.  But remember that I am using them (and not VTA...) for system-specific tuning.  Others might well prefer nice old ribbies (if they can find a nice pair...).  This tube position is definitly interesting on the ML2, and what "works the best" would very much depend on what the system-specific demands might be.  I think one nice thing about many of the older GE tubes I've tried is good consistency, other factors being equal.  But this can never make up for the liars and cheats who deal in the tubes.  For this and many other reasons, most people will have to buy and then try the tubes, with no real assurances of anything.  This sad state of affairs is just one of many, many reasons why I hate tubes.

Dare I even so much as mention the VTA reference again?  Sorry, but it does seem to want some closure, not just to spare myself humiliation (which I think I can deal with in this context), but because I don't want to mislead anyone.  Anyway, I certainly hope the VTA stuff I dragged in was clearer to others than it was to Romy.  To be clear: I do NOT mean to say that I do (or others should do) tune the system with VTA, because this is not only plain stupid, but it is the worst sort of aimless fiddling that could literally ruin a system if played out too long.  Therefore, I actually mean to say pretty much the opposite, that I have gotten a much better handle on system sound and capabilities since I have closed the gap on one more major sonic variable (the VTA), and I was thereby able to take the sound of the ML2s in a pre-determined direction, because I knew where I wanted to go based on a much more solid sense of where I was, using +/- reliable input from vinyl as source material.  That's it.  I already spent enough time on VTA versus the BEP delta to revisit this; a re-read there ought to put this into context, as well, for anyone who's interested in the "connection".

Lastly, I do not recommend messing with tubes while the amps are on!  In fact, I recommend shutting them down and then waiting for the caps to drain before futzing with the tubes.  But, to each his own...

Best regards,
Paul S
01-10-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 155
Post ID: 12665
Reply to: 12662
Cycling bias: Improvement
fiogf49gjkf0d
Romy, thanks, as usual, you seem to have been right.
 
The system is on and I just checked V2 voltage; its way off, above .4VDC, so I grabbed a hot pad from the kitchen and rocked the V2 tube. The socket made the familiar a dry creaking sound and seems nice and tight, though I wouldn't feel it if there were a single loose pin. The voltage changed with the rocking, which I continued to do, in all directions, for about 30 seconds. I then let the voltage stabilize, adjusted it down to .3VDC, and set the volt meter to take max high and max low readings over the period of one hour (a nice feature of Fluke meters). Results: Voltage now cycling between .252 and .294V, (.042V range). Over a period of 3-5 minutes, there is little change, so the situation has improved, but the reading is not as stable as in the case of the other amp, which cycled between .297 and .317V (.020V range) over one hour.
 
With the V2 reading brought back to .3VDC, the voltage for the regulator tube (V1) is dead stable.
 
The reason I renewed all tubes in the amps was that one of the V2 tubes failed, making the horns emit a very loud buzz. Fortunately I was standing near by, and yanked the power cord out of the back of the amp. I no longer let the amps warm up while running to the grocery store. The failure occurred in the amp that has the cycling issue; I suspect the failed tube was abused. I may need to further clean the socket. At worst I will replace all sockets (an operation I'm now doing on the L2 preamp, where a failed socket took out some capacitors... Currently using my old L1). It would be nice to know what, if any, potential dammage to other internal components could result from a failing V2 socket/tube. 

Paul, thanks for the tips; I don't currently have a backup pair of V2 tubes on hand (in France, the post office closes before I leave work... I need to get one of those old-school, stay-at-home wives so I can start using mail order!). I would say changing them out once a year seems excessive, but not if you're getting a second year of service in V1 position. 
 
jd*
 


How to short-circuit evolution: Enshrine mediocrity.
01-10-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 156
Post ID: 12666
Reply to: 12665
I think it just too fresh tube
fiogf49gjkf0d

There is one thing that you also need to consider. The way how in ML2 bias is built it is a bit tricky to set bias for a new tube. In ML2 a brains new tube will raise bias very aggressively and then it will return it back as the tube heat up (in 10-15 min). This initial elevation of bias is an indication the tube is new and good. The new tube need to be preborn with ML2.  I wrote about it many times.  There is high change what you call “cycling” is in fact a normal behavior of ML2. As the tube got burned a bit (30-50 hours I would say) then the elevation of bias will be minimized and eventually stop.

The rand new tube in ML2 you must not run hotter than 30-50mA after 5 minutes of operation. In 15 minutes it will rise to 200-300mA – that is normal. Keep the tube burn at 30-50mA unit the max rise will be no more than twice: 60-100mA. Only then you can set 300mA and run the amp as normal. In 5 min it will be 300mA, in 10 min it will be 360mA and in 15 min it will be back to the cruse 300mA, or to whatever you chose as operational current. The well burned tube after the 50-100 hours will have in ML2 the initial curls rise above the operational (it amp do not care signal) not more than 10mA and might be discarded. (The numbers are appropriate and vary from tube to tube)

Anyhow, do not make any judgment about your tube operation if it is very fresh tube. I do not think that it is contact problem as bias in fixed based tine is sent to grid pit and if you had bad contact or arc on grid pin then you signal will have bad contact. Grid pin never go bad on 6C33C, plate and cathode most frequent and filaments are very frequent -never grid. So, age the V2 tube and then see what you stay. I think the “improvement” you report is just your V2 is burning up and get more stable in operation.

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
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jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 157
Post ID: 12667
Reply to: 12666
Fresh 6C33C behavior ect.
fiogf49gjkf0d
I am familiar with the fresh 6C33C behavior, and I do set bias much lower while burning them in.
 
This set of tubes has been installed for about 3 months; the amps are operating about 45 hours a week.
 
Before switching them on the next time, I'll try swapping the V2 tubes from one amp to the other, and see if the cycling issue follows the tube. 
 
A possibly dumb question here: When you and Paul give figures in milliamperes, where are you measuring the current (at what points), or are you extrapolating the figure?
 
jd*





How to short-circuit evolution: Enshrine mediocrity.
01-10-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 158
Post ID: 12668
Reply to: 12667
In this case voltage and current are the same
fiogf49gjkf0d
 jessie.dazzle wrote:
A possibly dumb question here: When you and Paul give figures in milliamperes, where are you measuring the current (at what points), or are you extrapolating the figure? 
The 6C33C current is measured in mA. The way of measuring it in ML2 is to measure voltage in the test terminals that Lamm provide. The test terminals measure the voltage dropping across 1R resistor connected in series with 6C33C plate. It is very convent as I=U/R or in our case I=V/1. So, you measure voltage but it has absolutely identical numeric value as current and despite that you use mV-meter you read the true mA numbers.

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
01-10-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 159
Post ID: 12669
Reply to: 12667
Actually a Good Question
fiogf49gjkf0d
Jessie, you just set your DMM to VDC and put the probes in the holes next to V2.  Like Romy said, because of the clever arrangement, the reading you get in VDC corresponds directly to what you'd get if you measured mA (if you could actually measure it).

On my amps the original lettering on the amp's decks is still legible.  This clearly says .31VDC, and that's just what you want to see on your DMM screen, if you run your amps to "spec".  I happen to use 280mA/.28VDC from the points near V2, and 185VDC (instead of the "spec" 175VDC) reading from the holes next to V1.

Paul S
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jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 160
Post ID: 12671
Reply to: 12669
Thanks for the explanations
fiogf49gjkf0d
Thanks Romy and Paul for the explanations.

Paul, I of course did know how to measure the voltage from the test points; what I didn't get, was how you were coming up with the current reading.

Why do you run the V1 at 185V?

jd*


How to short-circuit evolution: Enshrine mediocrity.
01-11-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 161
Post ID: 12677
Reply to: 12671
The Factory System
fiogf49gjkf0d

Jessie, current is mentioned repeatedly because in the case of DC, and in this situation, the current is actually what one wants to meter out.  Lamm just gave us a simple way to take a reasonably stable, real-time "measure of current" at this point, which would otherwise be +/- impossible to do.  No slights were (or are) intended or implied regarding any of these (or any other) "test procedures", since the actual circumstances are, to my feeble mind, far more arcane than we have touched on herein.  I went for years assuming that all calculated values could always be measured and "verified" for working voltage and current, inductance, capacitance, etc., and I was amazed and remain quite confused to find that, for all intents and purposes, math is as close as one actually gets to "knowing" the actual operating "values" one cranks with figures throughout a given circuit.  Basically, it's Heisenberg, all over again.  Few people have the depth of understanding necessary to conduct meaningful electrical forensics or really design in audio circuits, and IMO fewer (far fewer...) can go from there to get "good" working results in hi-fi.  I consider myself to be looking up at the bottom rung of the electrical knowledge ladder, and to tell the truth I see myself as not much farther "up the ladder" with respect to hi-fi, either, with much to learn and little to "teach".  And I am not being modest here.  The past year has been particularly "enlightening" with respect to exposing to me my own incalculable ignorance.

Re, 185V V2:  I always, eventually, get around to fiddling with operating points in all my active gain circuitry, since this is such an important tool for shaping sound, including the character of the sound.  This gets back to Romy's facination with "plate loading", a rich field of inquiry, indeed, for those at a certain level of comprehension, and the certain road to ruin for the unprepared.  In the case of the ML2s, I am aiming for a sonic matrix that is - in my system - "the best" compromise between harmonics, harmonic integrity and a sort of general sense of FR "continuity" that the ML2s either are or should be particularly famous for, since they are head and shoulders above anything else (I have heard) in this regard.  I have dutifully recorded my findings, which attempt to speak to what is possible, conditioned by my own system's special requirements and its (and my own) limitations.  I will air a personal suspicion, however, that Lamm's "factory settings" are aimed at the people he (correctly) deemed most likely to buy his amps.

Best regards,
Paul S

01-12-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 162
Post ID: 12684
Reply to: 12677
Operating points etc.
fiogf49gjkf0d
Paul S wrote:
"...the current is actually what one wants to meter out..."


Yes, I know this, I just didn't understand how you were measuring current... I am familiar with Ohm's law, but didn't see where you were getting enough info to "build the equation". Its clear now.

"...Re, 185V V2:  I always, eventually, get around to fiddling with operating points in all my active gain circuitry, since this is such an important tool for shaping sound, including the character of the sound... I will air a personal suspicion, however, that Lamm's "factory settings" are aimed at the people he (correctly) deemed most likely to buy his amps..."

Well its easy enough to twist the potentiometers, sit back and listen... I'd want to make sure I weren't over stressing things down stream of the V1. I'll look into that level of fine tuning once all horns are in place, eating their carrots and peas, and properly installed in a room that really suits them.

Thanks again,

jd*


How to short-circuit evolution: Enshrine mediocrity.
01-12-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 163
Post ID: 12686
Reply to: 12684
Keeping It Real (Safe)
fiogf49gjkf0d
Of course, the safe and sane version of "twisting the pots" is to keep Ohm in mind the while with respect to total output (Watts). 

YMMV, but I've found that what I want at this point happens below 54 Watts.

Paul S
01-22-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 164
Post ID: 12748
Reply to: 12686
Punk Rock
fiogf49gjkf0d
For many years I have habitually "rocked" tubes gently in their sockets (when the equipment is off!) in order to "better establish the electrical connection".  I suppose I have done this hundreds of times with no problems, apart from three fairly recent, serious problems.  The problems were cracked tube bottles in two 5651s and just now on an old 6096 (6AK5).  Oddly, the 5651 failures were barely audible.  I happened to noticed each in its turn had "melted" inside.  OTOH, the 6096 failure was announced by two loud "pops", and I assume one of them was the internal "fast-blow" fuse, since the unit would not produce sound when I replaced the bum 6096.

Looking more closely at the cracked tubes, I see that the glass is pretty thin, albeit it is not nearly so thin where the cracks occurred in every case, on the bottom, in line with a couple of tube pins.

Because the rocking has become a +/- habit, I will have to TRY to remember not to do it now.

Anyway, now you've been warned; rock on at your peril.

Paul S
01-22-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 165
Post ID: 12749
Reply to: 12748
Do not fix it until it gets broken
fiogf49gjkf0d

To crack the small-pin tubes by jerking them in tube-sockets?  I do not believe in it but you are at your full right to feel that you did it. If you cracked 6AK5 then it will very fast (a few hours) loose the getter on the top of the tube (dark-silverfish residue). If you cracked 5651 tube then you have no Neon (or Krypton or whatever they use) in the tube and it will have ability stabilize voltage.  I guess it will bring some noise as well. Also, I think that if you did somehow cracked the tube by rocking tubes “GENTLY” in their sockets then you realty need to review your definition of gentleness.

Now, and I am not kidding. After this “gentleness” you certainly need to trash the current sockets as you have destroyed them. Initially, when you just felt a need to rock the tubes in the socket you needed to clear the socket and do not do any tubes jerking.

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
01-23-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 166
Post ID: 12750
Reply to: 12749
Verifying pin grip of tube sockets
fiogf49gjkf0d
Assuming that by rocking the tubes too aggressively, one might cause the socket to lessen its grip on the pins:
One way to check this might be to break open a set of dead tubes and remove a single pin from each, then hold each pin, one at a time, in small pliers, inserting it into each receptacle of the corresponding socket, verifying that the pin is being "grabbed" with adequate force.

jd*


How to short-circuit evolution: Enshrine mediocrity.
01-23-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 167
Post ID: 12752
Reply to: 12750
Not to Defend the Habit
fiogf49gjkf0d
Jessie, another thing is that there does not appear to be an actual  "standard" tube pin diameter for a given species.  Add to this the mediocre initial quality of the Lamm sockets and you have a less than ideal situation to begin with that cannot improve with time.  I noticed and reported quite a while back that I had to bend pins on an otherwise-OK batch of 6N6Ps with thin pins to ensure "sufficient" contact with all pins.  This was soon after I bought the amps, and it was certainly before rocking had time to affect anything.  To further confuse things, I had previously rocked tubes in a dozen amps over 45 years without ever cracking a tube or producing any other overt signs that the practice itself was a bad idea.

To be clearer (but not to seek exoneration), the rocking, though habitual and chronic, is not something I've done often.  Rather, I have done it only when I installed new tubes or while cleaning pins and/or sockets.  So any damage done by me in this case happened pretty fast, with but few occasions of the offending ritual.

However, all Sophistry aside, I think this is a case where the results speak for themselves: The broken tube bottles clearly indicate how "careful" or "gentle" I was (or wasn't...) in the cited instances.  And clearly, at least some of the 5651s and 6069s are vulnerable to the sort of "gentle" treatment to which I subjected them.

Of course the post is meant to be cautionary rather than confused or defensive.  Upon reflection, I should better have said my tube handling has been "deliberate" rather than "careful" or "gentle", since - again - the results speak for themselves.  Speaking for myself, I am going to really try to kick the habit.

Now, to find the effing 1.25A fuse (as opposed to the ubiquitous 1A or 1.5A one can get about anywhere).  'Guess it's another "factory" item...


Best regards,
Paul S
02-14-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 168
Post ID: 12932
Reply to: 12752
Voltage Question
fiogf49gjkf0d

Does anyone know the voltage the big couping caps actually see?  Yes, I should measure it, but I would rather avoid the drill of opening the amps, propping them up somehow and measuring if someone already knows the answer. Of course, I'm asking in order to get new caps in the correct rating.

Thanks,
Paul S

02-14-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 169
Post ID: 12934
Reply to: 12932
The coupling caps in ML2?
fiogf49gjkf0d
 Paul S wrote:
Does anyone know the voltage the big couping caps actually see?  Yes, I should measure it, but I would rather avoid the drill of opening the amps, propping them up somehow and measuring if someone already knows the answer. Of course, I'm asking in order to get new caps in the correct rating.
They are 400V-450V, I do not remeber exectly. The 6N6P most likely sit at 200V and 6C33C at 170V, so the 400V shall be enough.  The ML2 has double sided board and it might be a bit tricky to solder it.  If I were you then I would not remove the current caps and would not remove the board.  Cut one lead of the current caps in the middle. Then put the new caps in parallel to the uncut lead and to the lead that will be sticking from the board. Do not overheat the sticking leads as it might unsolder them. Be advised that it would take 2-3 weeks a cap to burn in. Also, confirm if ML2 has fist and second stage cap coupled and if it does (most likely) then you need to replace them as well. What cap will you will try to use instead the Lamm’s Cubes, the Duelund?

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
02-14-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #: 170
Post ID: 12936
Reply to: 12934
I could not "see" the Duelund
fiogf49gjkf0d

There are some very interesting moments with the not-so-expensive Sonicap Gen I caps, which I have described in the K&K thread. I will replace the 935s with these.  I am willing to take the chance that the little .033 uF 1000V 950s in my unit are just overrated bypass caps, and I will replace those, too, with the Sonicap Platinum teflons, since I now know this combination from the K&K.

Yes, yes, I know we're not supposed to use the same caps everywhere.  But I am presently thinking that the Sonicaps are simply more "correct" from an electrical standpoint, and I am willing to take a flier on them based on this (as heard, of course).

Good point about the potential for overheating/de-soldering the old cap lead stubs at the thru-holes; I will try to be careful when the time comes.  I have little heat sink clips that I use to divert heat from where it's unwanted.  I was actually thinking I could use my de-soldering gun to simply remove the old cap leads cleanly, but I would indeed be very pissed if I messed this up and wound up having to take the board out to make it right.

Like I confessed a while back, Duelund definitely had me at one point. I was totally hypnotized, ripe for the picking; but insufficient funds curtailed the madness.

Best regards,
Paul S

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jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 171
Post ID: 13111
Reply to: 12684
Bias current; rise during warm up
fiogf49gjkf0d
After swapping all the tubes between the left and right amps, the cycling bias current issue (mentioned here in a previous post) seems to have settled.

I now have another question, which I hope other ML2 users might answer; first the context:

These amps came with two complete sets of tubes; one that had been in use, and one that the seller claimed were new, purchased from Lamm. The tubes did appear to be new (I have the equipment to test them, but have not yet moved it out of storage). For the past 6 months, I've been running the amps with these "new" tubes.

When the amps have been in use all day, I can set the bias current for .31 and everything is fine. The following day, I switch the amps on, and within 15 minutes, the current will have climbed to well above .31 (I just measured .385 for example), and returns to .31 only after the amps have been on for over 2 hours. The climb in current during warm up is quite a bit greater with one amp as compared to the other, but I suspect this to be due to the individual behavior of each V2 tube.

With the "old" tubes installed, I don't remember having to fuss this much with bias current, but it is possible that I've become a bit psychotic since then.

Can anyone using ML2s tell me if their amps behave similarly; that is, do they rise well above .31 during warm up, and if so, is the rise in one V2 as compared to the other approximately equal?

You might be saying to yourself, "why doesn't he answer his own question by simply reinstalling the old set of tubes?". Installation of the "new" set was prompted by a failed V2 tube. I assume that the other old V2 is pretty close to dead, and I don't have an alternate set on hand.

Thanks in advance,

jd*


How to short-circuit evolution: Enshrine mediocrity.
03-08-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 172
Post ID: 13112
Reply to: 13111
I wonder why Lamm does it.
fiogf49gjkf0d

You have this behavior with the tube that you run for 6 month? That is strange. The behavior you described (with this amps) is typical for a very fresh new tube but after 20-50 hours  the amplitude of the current raise shall be minimum and and after 100 hours it I pretty much negligible.

http://www.romythecat.com/Forums/ShowPost.aspx?postID=6140#6140

I did not see a tube that behave as fresh as the new one and I did not see a tube that need 2 hours to stabilize current. It does not mean the do not exist and you might get one. If I were you then I would get a gamma probe and would try to test the tube for radioactivity….

I usually suggest to set your new 6C33C tube for operation of 250mA-270mA, use it for a while and only then set 300mA
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
03-08-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 173
Post ID: 13113
Reply to: 13112
The freaky V2s
fiogf49gjkf0d
Romy wrote:
"...I usually suggest to set your new 6C33C tube for operation of 250mA-270mA, use it for a while and only then set 300mA..."

This is what I did; in fact, I've had to leave them set at 250mA so that during warm up they don't go over 310mA. I think I got a hold of a couple of freaky tubes... I will try swapping them with the V1s.

I just poked around on eBay and it seems the 6c33C-B tubes are not so easy to find. There are however plenty of the model 6S33S-V. My understanding is that this is supposed to be a more durable version, intended to better resist vibration... Any opinions as to whether there is a difference in sound?

jd*


How to short-circuit evolution: Enshrine mediocrity.
03-08-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #: 174
Post ID: 13114
Reply to: 13113
6C33C-B vs. 6S33S-V
fiogf49gjkf0d

 jessie.dazzle wrote:

I just poked around on eBay and it seems the 6c33C-B tubes are not so easy to find. There are however plenty of the model 6S33S-V. My understanding is that this is supposed to be a more durable version, intended to better resist vibration... Any opinions as to whether there is a difference in sound?

Jessie, 6C33C-B and 6S33S-V are identical, in fact the very same tubes. The 6C33C-B is Cyrillic writing and 6S33S-V is just Western transcript of the very same tube. It is like feeling that “cat” and “chat” are different animals...

http://www.shinjo.info/frank/vs.html

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
03-09-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 175
Post ID: 13118
Reply to: 13114
So if S=C & V=B
fiogf49gjkf0d

That's good news.

ТХАНКС !

jd*



How to short-circuit evolution: Enshrine mediocrity.
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