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12-07-2009 Post does not mapped to Knowledge Tree
Lx_
France
Posts 33
Joined on 12-06-2009

Post #: 141
Post ID: 12436
Reply to: 12425
6C33C matching: first proposal
fiogf49gjkf0d
 Paul S wrote:

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

To do gain matching we need a way to measure gain. To be precise, we need to measure a value that is representative of the tube's gain. We don't need the absolute gain value (though having it would not hurt and would do the job perfectly, it is not strictly necessary). Then by using the representative value for several tubes we can select two that match "closely enough" (quotes used to underline that this is too vague to be used as is).

We have a quite sophisticated measurement tool at our disposal, albeit an expensive one. It's made by Lamm himself and is called ML2(.1).

Here is a naive suggestion: why not use it to evaluate gain? We could apply a sinusoidal signal at the amplifier's input. Measure the voltage at the speaker binding posts (output signal) and divide by the input voltage. This gives the overall gain of the amplifier. Not the gain of the 6C33C, but if we change V2 tubes, we have a function (overall amp gain) of only one variable (the V2 tube) and that should be enough for our needs.

Some problems I can see with this procedure:
- I am not sure the output voltage can be used (the amp acts not only as a voltage amplifier but also as a current amplifier)
- I don't know what tolerance we can use to determine that two tubes match "closely enough"
- not repeatable in time: if we measure a batch of tubes at some point in time, there is no guarantee that it will measure the same later on, because other elements change in time (other tubes...). This change is probably minimal and hopefully negligible. It that's the case, when receiving a new batch of tubes, it is sufficient to measure only the new tubes, and they can be compared to ones that were measured previously. Otherwise an old tube should be measured again and old measurements corrected accordingly.

Regards,
Laurent
12-07-2009 Post does not mapped to Knowledge Tree
jessie.dazzle


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

Post #: 142
Post ID: 12437
Reply to: 12426
Some ML2 & 6C33C ramblings
fiogf49gjkf0d
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.


How to short-circuit evolution: Enshrine mediocrity.
12-07-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 143
Post ID: 12438
Reply to: 12436
The gain of 6C33C is not truly important.
fiogf49gjkf0d

After trying all the might be tried with 6C33C (measurement-wise) I concluded that I know that tube very well …in order do not test it. All that I do is taking a new tube, burn it until the start up current is stabilized:

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

,then place in amp, set cruse current, turn on my tuner 1000Hz signal generator, set my preamp to reference attenuation level and measure with a dB meter what my MF channel outputs on the horn’s axis  and at mouth plane.  The R and L channels shall be with .25-.5dB (less is better) between each other and within .25-.5dB in relation to the reference point of my next channel. If I have more of less dB then I change the tube to another one. With some experience I can match even non-burned tube but it is tricky.

Laurent, your problem looks to me as you have faulty contacts in the amp sockets. True violently to swing all 3 regulator tube in the socket and to see which of them is faulty.  Yes, one more thing – do not substitute the fuses for larger current – VERY bad practice. This amp was not designed by  an idiot and the currents in there and the fuses in there as they shall be. If the amp blow fuses then it is good – it gives to you an opportunity to search and to find a problem.

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
Paul S
San Diego, California, USA
Posts 2,570
Joined on 10-12-2006

Post #: 144
Post ID: 12440
Reply to: 12436
The Hand that Rocks the Cradle
fiogf49gjkf0d
Laurent:
I would be VERY careful about "rocking" the 5651 in its socket in an attempt to establish better contacts.  I have "split" the glass envelope near the pins on a couple of 5651s doing just this and I did not realize it until the sound got scary, and when I looked over, the tube was "melted".

Jessie:
I would rather avoid  "rough" methods of "cleaning" tube  pins.  For one thing, it absolutely makes for more noise of another sort (micro-arcing?).  For another thing, it absolutely causes the tube pins in question to foul again that much more quickly.

The ticket seems to be chemical cleaning, and scrubbing with nothing rougher than Blue Magic (abrasive) polish, only if necessary.  And yes, one has to then clean all the abrasive off the pins pior to use.  And yes, it is a slow, burning PITA.

And I almost forgot to mention that the dielectric grease (after cleaning) actually does work better than nothing!



Best regards,
Paul           
12-26-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,570
Joined on 10-12-2006

Post #: 145
Post ID: 12557
Reply to: 12440
"Pinless" Tubes?
fiogf49gjkf0d
Anyone ever tried the "pinless" tubes that have long-ish wires in place of the usual pins?

A Moscovite I ran across has Russian mil-spec 6AK5 "equivalents" that have pinched glass and the wires instead of pins.  Oddly, Lamm lists the type numerically as interchangable, but I wonder: surely there are two versions of this type of "6J1P-EV" (actually, designation is Russian/Cyrillic...) tube, one with the usual pins and one with the longer wires.  Then I wonder how I'd connect them, and how I'd kep them not only connected but physically stable, to deter microphonics and self-noise.  Maybe the "EV" part of the designators describes the wires?

Maybe I should just solder the EV things in there, stop worrying about the lousy tube sockets?

Paul S 
12-27-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 146
Post ID: 12559
Reply to: 12557
Let the 6AK5 to be 6AK5.
fiogf49gjkf0d

 Paul S wrote:
Anyone ever tried the "pinless" tubes that have long-ish wires in place of the usual pins?

A Moscovite I ran across has Russian mil-spec 6AK5 "equivalents" that have pinched glass and the wires instead of pins.  Oddly, Lamm lists the type numerically as interchangable, but I wonder: surely there are two versions of this type of "6J1P-EV" (actually, designation is Russian/Cyrillic...) tube, one with the usual pins and one with the longer wires.  Then I wonder how I'd connect them, and how I'd kep them not only connected but physically stable, to deter microphonics and self-noise.  Maybe the "EV" part of the designators describes the wires?

Maybe I should just solder the EV things in there, stop worrying about the lousy tube sockets?

Paul, again, I am not sure that understand what you are trying to do. Why you are looking a substitute for 6AK5? The 6AK5 is a fine tube and there are many of them girt cheap. You can get the best western 6AK5 you wish.  If you have a problem with socket then you might replace them or you might clean them ONCE and use a socket saver. To go for a soft pin tubes on the areal amplifier of the regulator? What for? I had ML2 and I did felt that “better” 6AK5 give a very slightly different sound. Was it better sound? I do not think so. Also the difference was so negligible that I did not bother to play with it. I would understand if you try to use in there “faster” pentode but the 6AK5 is fast enough as it was made for IF amplification. I never had any problem with 6AK5‘s microphonics or self-noise, so I do not know what you are talking about. How do you know that you have microphonics in 6AK5, how do you measure it?

EV does not mean wires type.  You might get info about Russian abbreviations from here.

http://en.wikipedia.org/wiki/Russian_tube_designations

Still, I would not go for Russian tubes in the voltage amplifiers. You need to answer to yourself why you are looking into this direction.

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
12-27-2009 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,570
Joined on 10-12-2006

Post #: 147
Post ID: 12566
Reply to: 12559
"Aimless" Tubes
fiogf49gjkf0d
Just a lazy-ass type question, really, motivated by nothing more than curiosity.

Today, since it's "time to change the V2", and also out of curiosity, I will break in some "vintage" 6C33Cs.

To tell the truth, any logistical "issues" with ML2s actually have more to do with speakers, since I can't presently see any way to do FR the way I want using only one amp per stereo side. And Lowther dynamics are what they are, after all.

Also, fine electricity always - eventually - pops up and calms my misery, puts other things into perspective.

Best regards,
Paul S

01-09-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,570
Joined on 10-12-2006

Post #: 148
Post ID: 12655
Reply to: 12566
It's the Tubes (again), Stupid
fiogf49gjkf0d
I suppose this further erodes my "credibility" regarding the "tube sockets" hysteria, but it is what it is, so here goes:

Today I finally had the right combination of alone time and motivation (not to mention great electricity) and I got around to swapping out the ribbies (input tubes).

Circling in on this thread, it's been a while since I got the VTA to where it's satisfactory pretty much every side.  During this time I've been brewing a hunch about the input tubes; not just the "crumpled paper" noises, but I was also getting gradually diminishing bass, articulation and clarity, and the harmonics were no longer making up for the losses.

Based on the sense I was developing about the sound, I put the old GE alternates back in, the same tubes that wowed me the first time I tried them, then they seemed to let down, with sadly defficient harmonics.  Basically, I was thinking perhaps the "sadly defficient harmonics" might have more to do with the drifting tone arm/VTA and/or BEP than anything else, and I wanted to give this theory a try before I tossed any of my present input tubes.

Results today were interesting (and fun!).  I think this is the first time I have thought of instrumental harmonics and a particular sort of "patient" articulation in the same conceptual vein.  But this was the case today, with texture somehow an effective part of nice, spike-y treble and acceptable harmonics, too.  Bass was as good as I've gotten from my system, just as it was the first time I used these old GEs.

As for the "vintage" 6C33Cs, that's harder to say.  I did try them before I swapped the input tubes, and it seemed like they are "tighter", in the audiophile sense, but without the stripping that this usually entails; keepers, but no somersaults.  They do seem to be quite well matched with respect to gain, although they were not represented as "matched".

Electricity was fantastic for 3 hours today, and of course this is a big factor; but it was also great last week, with the ribbies still in.

The ever-annoying truth of it is that tubed gear is an ongoing PITA, and the more tubes, the more BS with those tubes.

How funny that some people collect the tubes just to own them, like fetish objects, and some people love just the idea of "tubed gear".  I say it every so often, and it's still true, I would put tubes in the rearview and never look back, and I would go 100% SS if I could figure out how, in terms of sound.  Funnier still, there is nothing about the sound I am aiming for that I connect specifically with tubes, per se.

How much are people paying for carefully-matched NOS Telefunken ribbed plate pairs these days?  I guess they cost what they cost.  New ones work nice in the ML2, but no way I got anywhere near 10,000 hrs. from those tubes.   No way I got 1/2 that.  Since I never heard that the ML2 eats its input tubes, I ass-u-me that the particular tubes I bought were either more used than they were represented to be, or they just burned out faster than "specs" said they would.

Oh, well, that's tubes...

Paul S

01-09-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 149
Post ID: 12656
Reply to: 12655
Wey! Where to begin?
fiogf49gjkf0d

Pall, stop to talk about VTA when you are talking about amplifiers and stop talk about VTA when you are talking about electricity. Sorry, it sounds juts insane. VTA is a subject of interaction between a records and cartridge; it is not the subject of the rest playback. Do not use VTA to “cure” the other problems of your playback as it sounds foolish.

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=45

The 12AX7 in input stage is in my view the only tube truly worth play in ML2. Ironically the cheap GA 12AX7 tubes are not bad. They look very plain and cost nothing but they have very nice and stable sound.

About some people are collecting tube… yes and no. I understand that curiosity made people to buy different tubes but then laziness made them do not want to sell them. I did accumulate a bunch of the tube for my DH DSET MF project and I do not need 95% of them. However, I do not see myself going to people, to sell those tubes, answering questions, worrying about shipping and so on. It is much easier to dump them in a box and forger about them.

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
miab
Canada
Posts 46
Joined on 02-07-2008

Post #: 150
Post ID: 12658
Reply to: 12656
12ax7 brand?
fiogf49gjkf0d
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?
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 10,049
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 10,049
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 2,570
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 10,049
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.
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Romy the Cat


Boston, MA
Posts 10,049
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 2,570
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.
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