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

Post #: 61
Post ID: 14904
Reply to: 14903
Axiom and EL34
fiogf49gjkf0d
(Romy feel free to move this post)

 Paul S wrote:
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.


Paul, I'm not really sure how specific it is. I think you are mistifing it a bit ;-), but it's also quite possible I don't understand the circuit at all! At a risk of making an idiot out of myself (which is not a big effort) here is how I see it:  DC coupled, choke loaded, stacked power supplies. The gross of the biasing voltage is generated as a voltage drop on the big DCR's of the loading chokes. This is something that stacked supplies allow! Very smart, but IMHO requires stability. Then, the remaining voltage is generated via autobias, but in order to diminish the effects of the cathode feedback, diodes are used instead of resistors (lower dynamical R than statical). The diodes are generic, cheap  TV dampers (apart from the lowest one as it sees lower current), nothing special. Most probably they were chosen in a very simple and natural way: to give the desired voltage drop at the chosen questient current. That's all. Look in the tube manuals and pick a (good, linear) diode to do the job. There is a very educational article of Steve Bench on diode biasing:

http://greygum.net/sbench/sbench/dio_bias.html

There is no magic in that. I'm not sure why you think the diodes are so special about this design and constitute it's core and say the "diodes coming and going, to maintain balance, isolation and stability ". Perhaps I'm wrong  but a cathode resistor also gives a "balance and stability". This comes from the autobias per se, not from a particular way of implementing it. I've been simulating my circuit for quite some time now. It does seem to behave...on a screen at least Wink
If the line voltage rises, rises both driver and out currents. More driver current=more drop on the choke DCR=more bias on the out counteracting the current rise. Simultaneously, the  autobias provides a second mechanism of autobalancing in the usual way, but less efficient, since only  small percentage of the bias is generated there.
What do you mean by "isolation" and why biasing diodes provide it I'm perhaps too stupid to see.
The mysterious thing I refuse to understand is whay the've put a second 6CG3 in the plate?
Then the power supplies are nothing special at all: tube rectified, generic 5U4 crap, (pseudo)-choke input, big, i.e. not 10uF, but still nothing compared to Romy, caps, reasonable volts. First choke of course has to "swallow" quite some volts, but that's normal, it's a choke-loaded supply (actually the small cap makes the job easier). What is different here from a 1000 other properly executed choke-input supplies?
Mind you I've managed to construct a 872A choke-loaded bridge supplying 1.5kV for 304tl (I'm an idiot, I know), so this looks like a toy :-) I've designed the tranny and the chokes myself. They worked. What for? To satisfy my stupid wet dreams...
I don't follow your worries of tank circuits generating lots of volts and noise. Power supply ones?
Then the tranny. Paul, what is so terryfying about it? They put all the 3 supplies on one core so it must be big if done right, but nothing abnormal. Then lots of tubes floating require lots of separate heater windings, so the heating tranny is big too, but again nothing abnormal. For my winders 100Eu is a lot. They will wind quite complicated power if I provide clear instructions. The are also old stocks of good cores, good cut core or toroid is enough, no amo crazyness, I don't want to listen to the power transformer anyway (Romy style PS, 10000uF). The careful routing (high volts) and esp. the grounding is a chalange, I agree. 1kV RF cable helps here. I have loads of it.

 Paul S wrote:
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.


Very encouraging comments on the neutrality and transparency! Thanks! I wanted to put it in the triode mode, at around 400V, 40mA. Remember it's a headphone amp I'm trying to cook not a speaker one, so I don't really need more volts, no need to stack the tubes. Max in triode mode is 425V (the screen limits here).  Another candidate would be 300B, but it's stupid price and audiopedophile sound disqualifies it. Boutique tubes...let them power boutique amps, not mine.

Cheers,
N-set



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 #: 62
Post ID: 14905
Reply to: 14904
Shock and Awe
fiogf49gjkf0d
N-set, clearly you have a much better understanding of electrical engineering than I do (as do most of my pets...)!  Still, I am hardly terrified by tank circuits, just wary of inter-component/PS/signal mosh.  And I really don't care what sort of divider someone wants to use, but I think the Axiom axioms actually happen to stress diodes, and you have cited the reasons why.  Those chosen were said to be "linear", as diodes go, for the particular application.  And since you mentioned Steve Bench, you probably know he used diodes for his phono stage.  I say, good design allows some "slop", and I also like to be able to put hands on my operating points if I want to.  OTOH, I am not putting hands on anything inside a chassis sporting 1.5kV!!!  I hope you have some serious rubber gloves, and I hope you're ready to watch that PS on your TV!

I also admit ignorance as to how a simple resistor supplies constant voltage given (potentially) fluctuating current...

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 #: 63
Post ID: 14907
Reply to: 14905
Confusion
fiogf49gjkf0d
Paul, electrical engineering has as much to do with Sound
as pimples on my ass with craters on the moon Big Smile !
I think I understand our confusiona: you've probably seen some earlier circuit
perhaps with one big 700V or 800V choke-input
supply and then RC circuits dividing the voltage between the stages!
Their new circuit employs three independent power supplies, stacked one on top of the other.
I'd think their stressing of diodes is somewhat of a marketing. 6CG3 are regular, cheap,
easy to get but supposedly very good TV dampers (I've never used them).
Cheers,
N-set





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 #: 64
Post ID: 14908
Reply to: 14907
Your Own Case
fiogf49gjkf0d
N-set, actually, I have seen a stacked-L schematic like you posted, with stacked caps layered over and R at earth for the tank, and I am on record as saying it is very elegant.  So, sorry to be such a skeptic, but I learned a long time ago that the only way to know for sure what happens with a real circuit this complex is to build it and run it how you want to run it.  I was thinking the cathode diode is +/- a "follower" (what I call "deniable feedback"...), and I would not bet on alternate versions.  In fact, I spoke with a guy not long after he heard that amp and he said it was not special, at least under the circumstances, which the designers, after all, controlled, and he also said they seemed happy with it. Well, I can certainly live with "not special" if it simply gets the job done for me; but who knows?  You say you are OK with the mains tranny, and I am OK if you are OK with special winding it, and I hope you are also saying it will be cheap!

But never mind all this; you want to stack just two stages (?) for headphones only, and your idea appears to "work" into an actual capacitor!  You can zap a long arc off an EL34!  Now, if your circuit runs predictably and quietly into a real-world reactive load, with a real ground tail, you're home free!


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 #: 65
Post ID: 14909
Reply to: 14908
Real world
fiogf49gjkf0d
Paul, 100% agreed on the real world test vs all other mental exercises!!!
Not sure on what do you mean by the "follower"?
Yes, I need only 2 stages, perhaps TVC at the input. I'll even have a bit too much gain, if I'm correct.
Romy style bias on 6E5P and PS: LCRC with 10000uF, decoupled somehow (Arcotronics caps, Obligatto...)
The design is actually elastic: if DC sounds crap, one can insert an
interstage tranny and decouple the supplies, moving to fix bias on the output.
If it all sound crap, will throw it out of the window and forget.
The heart is the loading choke for EL34. I don't know actually how to much voltage swing
in reality the headphones will need, so I assumed the worst case scenario (perhaps stupidly):
amp max=700V @20Hz. I also want to open a gap to linearize the core and accomodate the eventual imbalance.
This results in a mastodont choke, but I do have left huge amo cores after my 304tl wet dreams.
Now, how to make it pass HF is another story. I think of 4 sections (2 per coil), layered. The sections
will be quite compact, but communicate through the big core---electrostatic shield at the core pehaps? I did have +/- ok
results with big, sectioned and layered chokes---one of a size of newborn's head gave me 200kHz with 801A.
Choke is not a tranny, it's easier to make.

Cheers,
n-set



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 #: 66
Post ID: 14912
Reply to: 14909
Limits
fiogf49gjkf0d
Well 10k PS and 700V out ought to do it for headphones, all right (!), and the chokes ought to crank enough EMF to stand your hair on end at ten paces.

Not sure why you need to fight DC, but...

I already told of my own preference for bias adjustment options, because real tubes are all over the place, and because ultimately you have to sneak up on the sweet spot(s).

I, too, love amorphous cores and pure wire.

"Easier to make..."  That's funny.  They'll have to ship it on a pallet.

Best regards,
Paul S
Page 4 of 4 (66 items) Select Pages:  « 1 2 3 4
   Target    Threads for related reading   Most recent post in related threads   Forum  Replies   Views   Started 
  »  New  6C33C myths: audio Moronometr...  Overdrive warning light...  Melquiades Amplifier  Forum     3  42986  06-22-2005
  »  New  The short "6C33C Survival Guide"...  Ac filament.....  Melquiades Amplifier  Forum     20  274065  12-18-2007
  »  New  A different breed of 6C33C amplifier...  6C33C mono block @ clipping...  Melquiades Amplifier  Forum     84  686247  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  20078  01-09-2012
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