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11-03-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 41
Post ID: 14840
Reply to: 14839
Reverse Engineering
fiogf49gjkf0d
N-Set, I don't know about the 6C33C for tying directly to a load like that, if only because of its propensity to drift all over the place.  My own limited experience with this tube suggests that there is indeed a "sweet spot", but I am pretty sure you could not hold to it under the circumstances you propose.

It might in any case do to get the best "active" model you can for the speaker/load and then work backwards from there.  30H on a plate sounds downright bizarre.  How can this be a good idea?  Maybe better to stack more tubes?  6L6 or EL34?  Anyway, try to think like a capacitor...

Best regards,
Paul S
11-03-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 42
Post ID: 14841
Reply to: 14839
Since I do not get electrostats...
fiogf49gjkf0d
N-set,

if you use PP directly coupled to a GIVEN capacitive load then you might find it interesting to talk with Dima. He told me about his very cool idea how electrostats (that are notoriously capacitive) might be driven directly from plate. The idea is not new but he proposed to make it differently and I did not see it done anywhere in a way he described. I did find it very elegant but since I do not like electrostats I did not make any further thinking or experimenting with 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
11-03-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 43
Post ID: 14842
Reply to: 14840
30H & EL34
fiogf49gjkf0d
Paul, would you think 6336 will be more stable/predictable?
Have you had any experience with it?

30H: sorry, forgot to mention that the PP pair is autobiased
with a common 900R resistor...

EL34: indeed it's a very popular tube for driving Stax electrostats (Stax T2, blue hawaii, no idea
on their sound though), but 5x or so lower the internal resistance of 6336, 6c33c etc is appealing, esp
with a fast driver. I would not like to go into 300B or 845 crazyness and 801A has a highish internal resistance.

Romy: sure, would love to talk to him! Due to the space I'm limited to headphones if I want
to listen to anything, and then electrostats seem to be the most promissing...a sort of a
negative deduction choice.

Cheers,
n_set



Cheers,
Jarek
11-03-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 44
Post ID: 14843
Reply to: 14842
Headphones...
fiogf49gjkf0d
I don't know the 6336, but EL34 used correctly will sound like its driver tube, not to mention the comparative ease of PP scheming.  Sure, you need the voltage; but this to me only underscores the low ESR angle.  And who needs an inductor/transformer the size of a toaster?

Best regards,
Paul S
11-03-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 45
Post ID: 14844
Reply to: 14843
6E5P stability
fiogf49gjkf0d
BTW, how stable 6E5P is? I'm asking as I was contemplating biasing
the output by the voltage drop on 6E5P's plate choke (DCR is say around 1k),
with only some minimal autobias on the output. The drawback is that any drift in the driver
will rebias the output (I'm all the time assuming DC coupling with stacked PS).

Cheers,
n-set 
 



Cheers,
Jarek
11-03-2010 Post does not mapped to Knowledge Tree
deemon
Posts 23
Joined on 05-24-2004

Post #: 46
Post ID: 14845
Reply to: 14842
OTL electrostat amplifier
fiogf49gjkf0d
Yes , I told Romy about this funny idea , which is quite simple of course - to make a simple SRPP stage on special hi-voltage tubes , powered with high voltage supply ( 10000 V , for example ) and drive the electrostat panel directly from the output . The main thing here are the tubes , and I know only one Russian tube of this kind  - GP-5 , high-voltage regulator triode http://www.qrz.ru/reference/tubes2/type1/gp5.shtml , it has been used in old colour TV-sets , in the high-voltage regulator circuit for the picture tube . Of course , it must have many analogs in other countries ( and they can be even more suitable for audio amp ) , I don't know their names but I think that it's not a problem to find them . The main problem with this idea it that I haven't any electrostat speaker here to try , so it can be only a "theory" , of course ... And another point - we can use this ultra-high voltage amplifier only for big electrostats , like Quads , for example .... but for headphone electrostat we don't need such a voltage , so we can use the SRPP stage with more usual kind of tubes . 
Best regards 
Dima
11-04-2010 Post does not mapped to Knowledge Tree
manisandher
London
Posts 156
Joined on 09-05-2008

Post #: 47
Post ID: 14846
Reply to: 14845
EAR direct-coupled amp
fiogf49gjkf0d
Hi Dima,

Do you know if this is similar to the approach Tim de Paravicini took in his direct-coupled amp placed inside a Quad? I'm currently using Quad speakers (I gave up on the horn approach through sheer frustration) and it seems to me that this is a great way to go...

Mani.
11-04-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 48
Post ID: 14847
Reply to: 14844
About the 6E5P stability
fiogf49gjkf0d

 N-set wrote:
BTW, how stable 6E5P is? I'm asking as I was contemplating biasing
the output by the voltage drop on 6E5P's plate choke (DCR is say around 1k),
with only some minimal autobias on the output. The drawback is that any drift in the driver
will rebias the output (I'm all the time assuming DC coupling with stacked PS).
n-set,

the question about the 6E5P/6E6P stability I asked myself as well, what I was constructing with DHT version for MF. If you look MF channel of 6ch-Milq

http://www.RomyTheCat.com/TreeItem.aspx?PostID=10915

… then you will see that DHT tube is direct compiled and failure of driver tube will burn out  the output tube, in my case the rare and expensive 4V DH tubes. Yes, I put 100mA fast blow fuse on B+, just in case, but so far I did not have it blowing because a catastrophic failure of  driver tube. As you might see I use 6E5P/6E6P everywhere and since 2004 I went over I think 2-3 dozens of them. Some of them were very severely abused by a Moron with soldering gun (means me), I made many mistakes while I was experiencing with Melquiades and there were events when  6E5P/6E6P were running with no bias and as the result had anode with the temperature nears of Sun surface. Surprisingly, after cooling the tubes still forking fine, even though I did not put them in amps after that.

Uselessly what I take a new 6E5P/6E6P I test them.

I uselessly go the second posts of this thread

http://www.romythecat.com/Forums/ShowPost.aspx?postID=4805

…where the test data is located.

I usually test them at 4V bias, not the 3.4V as I wrote in the post. The 4V is how they run in Melquiades.  The good new tubes have GM around 19000, the well works tubes, after one year, have around 17000. The tube that approach 16000 are candidates for replacement but I sometimes replace tubes with 17000 GM. I look if the tube is old and if it has too much darkness built up on the glass. It might be not right way to do but I have many of those tubes – so why do I need to collect them? Live of high-end audio person is about who accumulate more tube before then die – I do not want to be a winner in this competition. I will be very comfortable if at the time of my final hart attack I will not have any tubes left….

Now, about the rejection rate. For all time I had one or two 6E5P/6E6P that I trashed right from beginning as they were not useable.  Another one or two tube did not give sufficient current. I generally would like to have 35Ma at 4V bias, if tune do not give it then I use it in A, B, C, D channels of 6ch-Milq. I need a full 35mA for single-stage amps of Melquiades. The 6E5P/6E6P are Russian tubes and as any Russian tubes they have notoriously wide parameters. The 6E6P-DR shall be military tube and shall have much less spin off the parameters but it is not what I see. What is good about those tube is that if you get one that operate as you want then it will most like to maintain this operation mode very stable. At least I did not have any single 6E5P/6E6P that failed on me after it was accepted on duty.

It might be no a lot but this is all data that I have. The tube is not used widely for a long time. The history of it’s use in high-end audio started in 1999 what Dima “discovered” it for audio. There is no known to me motioning of this tube in audio before.  If you plan to use 6E5P/6E6P then a tube tester (I am sure you have)  and it will be sufficient for initial filtering out the bad tubes, then they shall be working fine.

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
11-05-2010 Post does not mapped to Knowledge Tree
deemon
Posts 23
Joined on 05-24-2004

Post #: 49
Post ID: 14866
Reply to: 14846
Direct-coupled amp
fiogf49gjkf0d
 manisandher wrote:
Hi Dima,

Do you know if this is similar to the approach Tim de Paravicini took in his direct-coupled amp placed inside a Quad? I'm currently using Quad speakers (I gave up on the horn approach through sheer frustration) and it seems to me that this is a great way to go...

Mani.
Hi Mani , I don't know about it and never heard it before ... Maybe Romy knows more ? 
Best regards 
Dima
11-06-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 50
Post ID: 14868
Reply to: 14847
Drifting and loading
fiogf49gjkf0d
Romy, I'm of course familar with your MF design and Jim's 6E5P curves is what
I base my considerations on at this moment (along with the corresponding Spice model).
Your DHT MF is quite self-balancing due to the large cathode resistor. What
I have in mind is a deifferent topology (derived from Chimera's Axiom
http://www.chimeralabs.com/images/axiom.sch.jpg), which looks like much more sensitive
to the drifts. I post my lamentable approach here (feel free to (re)move it)

(I have problems with uploading the gif to the gallery so I attach it).

Most of the output's biasing is due to a voltage drop
on a big, 1.2k,  DCR of 6E5P's chokes. Then follows a small selfbias with 150R,
which will not be efficient in correcting driver's drifts.
But what you say is encouraging:

"What is good about those tube is that if you get one that operate as you want then it will most
like to maintain this operation mode very stable."

As for the loading: thinking as a capacitor, voltage is what drives me, so I need
a constant current source. Paul, I'd have less problems accepting a huge choke
than e.g. a transistor CCS. I do in fact have in mind a choke on a huge amorphous core,
but heavily sectioned (and interlayed), so in reality a collection of small coils on a common core.
As for active tube loading in SRPP, I have no experience with
it, but IIRC in a more standard application of an input stage, it had some sonic problems,
which some people tried to link to a specific harmonic spectrum of SRPP. No idea if that
would apply to the current context though.

Best,
N-set






Cheers,
Jarek
11-06-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 51
Post ID: 14869
Reply to: 14868
Sorry, I am off the game.
fiogf49gjkf0d
N-set, yes, I did not have any single 6E5P or 6E6P filed on me since it was accepted to operation. About your circuit – you need to talk perhaps with Dima or with others about it. I am absolutely not familiar with PP amps, I do not even understand how they work. Dima has 6E5P in SRPP ruining got years driving SS and GM70. I think you will have fun to talk with him about it.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
11-06-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 52
Post ID: 14870
Reply to: 14868
Diodes
fiogf49gjkf0d
N-set, I could not raise the attachment.  It has literally been years since I saw the Axiom (SET) circuit, but as I recall, it works with (tube!) diodes coming and going, to maintain balance, isolation and stability in the face of a classic "stacked" (1-way) tank circuit.

Do I remember a truly stupendous mains tranny, the likes of which one seldom sees this side of a power plant?  That'll cost ya'!  I think I remember as smart a grounding arrangement, per se, as I have ever seen, except no margin for error with the parts.  I for sure remember lots of diodes...

I am no expert, but I wonder about noise, trying to crank so much voltage off that particular tank, along with the whole +/- PP issue, and how that might do with the stock ground scheme.  If you want high voltage at the tube, maybe Deema's "TV" ideas are not so wild, after all, or even TV dampers, for that matter...  Start building that Faraday Cage!

Best regards,
Paul S
11-06-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 53
Post ID: 14871
Reply to: 14870
Diode or not, doesn't matter!
fiogf49gjkf0d
Paul, I've managed to glue the image:
stax_DC.gif`
Diodes or resistors is absolutely secondary to me, I wanted to try
the main idea. You seem to have good experiences with EL34, right?
Cheers,
jk




Cheers,
Jarek
11-06-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 54
Post ID: 14873
Reply to: 14871
Pentodes
fiogf49gjkf0d
I have never used EL34 in triode, but I think it is not hard to find acceptable examples of this fast, reliable tube, and with conservative bias it should let your 6E5P "shine through", if that's what you want.  Nothing like 811, 845, etc. in this regard.  More like "nothing"...

I thought one of the main ideas of the Axiom is that amp stage operating points are stacked (same polarity) along with the ground "planes", which use RC to "stack" over one another and true Earth, and diodes for isolation?  Not that you should stick to the axioms...


Best regards,
Paul S



11-06-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 55
Post ID: 14874
Reply to: 14873
Axiom and diode bias
fiogf49gjkf0d
Paul, below is the Axiom. I must say I've never heard it nor know anything
about the objectives behind the amp. I've just found the topology very elegant
and appealing. As far as I understand, the diodes
are used for biasing rather than resistors because the signal will see several times
less of the cathode feedback (low dynamical R of a diode), but at a price of
the added distortion due to the diode non-linearity. But anyway, most of the biasing V's
are produced on the loading chokes DCR's. Very elegant! But the driving tubes have to
be quite stable if I'm not mistaken.

Encouraging comments on EL34...what I've heard were mostly bitchings.


axiom.sch.jpg
Cheers,
jk



Cheers,
Jarek
11-07-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 56
Post ID: 14879
Reply to: 14874
Radar
fiogf49gjkf0d
N-set, I am tired right now but I think part of the "idea" is that all the parts will be perfect, with extremely low distortion into radar range, including specially chosen diodes, not to mention the big caps and wide-swinging Ls.  And where will they get that mains tranny!?  Ironically (these days...), LF does not math into infra...

Being ignorant, I thought typical tank circuit caveats apply here, too; "balance" does not preclude drift; leakage = noise, etc; all for one and one for all... 

I do like the EL34, but it is not a cause of mine.  I just tossed it out there because of your own requirements you've mentioned.  I realize it is not the tube-du-jour, just consistent and fairly easy to use.  What's hot these days? Gold-pin 50s?

Best regards,
Paul S
11-10-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 57
Post ID: 14900
Reply to: 14879
Milq. MF biasing
fiogf49gjkf0d
Romy, may I ask you why you've employed an autobias on 6E5P
in Milq's MF rather than your biasing technique (if there is any reason at all)?

Paul, I don't think I'm following you, but anyway I didnot want to analyze the Axiom,
but rather learn about 6E5P stability in DC amps :-))
EL34, I have been thinking of it for quite some time, as it has very good
"electrical" parameters for my intended application, but I've been of an impression
that it sounds poorly and not up to good triodes. Maybe poorly driven?


Cheers,
n-set



Cheers,
Jarek
11-10-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,650
Joined on 05-27-2004

Post #: 58
Post ID: 14901
Reply to: 14900
I think it was fine solution.
fiogf49gjkf0d
 N-set wrote:
Romy, may I ask you why you've employed an autobias on 6E5Pin Milq's MF rather than your biasing technique (if there is any reason at all)?

If you look at the page #13 of the Milq DHT thread then you will see that the first 12 drafts of the DHT Milq were with my typical biasing technique – a resistor in grid. Knowing your agenda I assure you that I went for auto bias not because the consideration of stability. In case of DHT I do not drive 6C33C with 70-90V of bias but a flimsy DHT with sub 40V bias. The full blown 6E5P has 32 times gain, with a good input voltage I was in danger to drive my DHT to class A2 – something the I did not want to. The option was to go for different type of driver tube with less gain of to go autobias on 6E5P. The autobias is very bad configuration as it employs a cap on cathode – very bad for sound. But if you look my autobias then you will see no cap. With no shunting capacitor on cathode a tube loops gain a lot – which was exactly what I was needed for my driver tube. So, I have the autobias but with no capacitor in cathode. This taupe of autobias is not different then my “typical biasing technique”. In my typical biasing technique a signal flows across a single resistor. In my version of the autobias the electrons flow to cathodes from ground comes also across a very small resistor. I think it was fine solution.

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
11-10-2010 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 59
Post ID: 14902
Reply to: 14901
Memory
fiogf49gjkf0d
Ah, ok! I've forgot about your gain considerations...




Cheers,
Jarek
11-10-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,216
Joined on 10-12-2006

Post #: 60
Post ID: 14903
Reply to: 14900
DC
fiogf49gjkf0d
N-set, I understand you do not mean to hijack the thread with the Axiom, so I actually tried to make generic and/or thread-related observations.  I don't know the 6E5P, but generic issues with specific DC tank circuits and driver and output tube stability therein remain.  The Axiom appears to address and capitalize on specific/generic issues in very specific ways, and - not to presume - it is perhaps not a great candidate for a generic, mix-n-match approach.  YMMV, etc.

As you obviously know, EL34 can be used in triode, and it has been my indirect understanding that its electrical parameters hold, as far as triode configuration makes use of them.  I would not use the EL34 if I wanted specific sounds from the output tube, itself, but I do "recommend" it as a potentially "neutral" output tube with electrical advantages that can be electrically relied upon, if that is of use to you.  "Sounds poorly" might describe the "sound of the EL-34" where it is made to have a "sound", or perhaps, even, its situational lack of a sound reveals undesirable else.  In any case, I believe it can be "neutralized" by sticking to - or at least starting with and tweaking from - its optimum operating points, as listed in the manufacturer's tube manual.  And, like I said in the early going, I would sooner stack tubes than stress them.  Who knows, you might even re-think the going-in bias against pentode operation in this particular PP application, at least for output.

It might be worth getting ahold of an old RM-9 (or similar output tube mule), to play with, to get a sonic/electrical "feel" for the EL-34 with your driver of choice.  I must say, however, that the 6C33C should also do "fine", given the proper use in the right circuit and a large enough supply of them. Like I said, I don't know about the 6C33C in a DC tank circuit...

Best regards,
Paul S
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  »  New  6C33C myths: audio Moronometr...  Overdrive warning light...  Melquiades Amplifier  Forum     3  42957  06-22-2005
  »  New  The short "6C33C Survival Guide"...  Ac filament.....  Melquiades Amplifier  Forum     20  273870  12-18-2007
  »  New  A different breed of 6C33C amplifier...  6C33C mono block @ clipping...  Melquiades Amplifier  Forum     84  685767  09-06-2011
  »  New  6C33C socket types, where to get the ideal one?..  Not so much the material that matters to me but the pin...  Melquiades Amplifier  Forum     2  20059  01-09-2012
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