[quote author=Eli Duttman  link=1134139974/0#11 date=1134219769]

Astro,

When you bridge, each amp section "sees" only 1/2 of the load.  Half of 3 Ohms is 1.5 Ohms.  "Vanilla" SE84 circuitry should not be used below 2 Ohms.  Toroidal autotransformers that match speakers to amps (impedance wise) are available, but they increase your costs significantly.

IIRC, Mr. Deckert used Hammond 270FX power trafos in quite a few SE84s.  The Hammond 270HX has windings with the same voltages as the 270FX at a higher current capability.

Use a 5AR4 as the rectifier.  Use 15 muF. as the 1st filter cap.  Follow the 1st filter cap. with a pair (1/channel) of 2 H./100 mA. chokes.  Follow each of the chokes with a cap./resistor filter network.  The arrangement described is known as pseudo dual mono and it makes for GOOD separation between the 2 channels.  
[/quote]


Since any additional iron to a "Zen-based" circuit would require a larger chassis, in addition to Eli's excellent suggestion, you'd have room to try a few other things as well:
1) replacing the EL filter caps in the power supply with Solen fast films - after my first breadboarding of a "ZenClone" using cheap EL, I tried the Films and never looked back.  Being located in Canada means the Solens are cheaper for me than the Sprague Atoms that Steve uses, and I daresay worth every penny.


2) replace the cathode bypass caps on each of the output tubes with 470mf Xicon  ( don't forget to double the size of the R when not shared )

http://www.geraldcurtis.com/images/Audio/Select-EX/7ElnaCerafineInstalled.JPG

3) triode wired EF86 for driver - Eddie Vaughn can provide the details;  I've used his suggested circuit on a couple of homebrews, and it's very, very good.  The only downsides are that it's not a dual element tube, and has a completely different pin configuration, and doesn't have enough "lead in it's britches" to drive every tube out there, but sure works with the EL84/SV83
4) Parallel feed

 
5) send Steve $20 for borrowing his circuit  :D

chevelle:

The EF86 as a driver would not be an addition, but rather a substitution for the very good 6N1P.  I can make this recommendation because in my own experience with "cloning a Zen"  (there I said it, I'm guilty  :(  )

Earlier this year I made a series of amps, based on the Zen circuit (due to both it's simplicity and the fact that I'd heard several examples of the Select and was impressed every time)  My first go-round was a stereo chassis, using entirely recycled transformers and tubes, and embarrassingly cheap new components for power supply (EL caps and resistors).  The final tube compliment was 40yr old EL84s and a variety of 6DJ8, 6922 and 6N1P of newer vintage.  

Based on hundreds of hours of scrupulous research  :-X , actually careful reading between the lines of posts of a certain Decware contributor, and several private correspondences with same, I decided to try the EF86 on my next project.  Since the parameters of the recycled iron I was using necessitated construction of mono-blocks, the lack of twin sections in the EF86 was a non-issue.  

Remember that the primary application for this tube was in low-noise microphone preamps.  Not the highest MU tube in the world, but it has sonic qualities that more than make up for it, and my system includes a Bottlehead Foreplay type pre-amp with substantially more gain and output than I need to fully load the amp to clipping.  Is it as dynamic and punchy as a 6N1P or 12AX7 (shudder) might be?  Maybe not, but as the humble OVK might say, "it might not model good on paper, but dam if it don't work good"


As for the parafeed, well I can't remember whether the idea was officially sanctioned or approved by any  forum members (here or elsewhere), but I took a gamble and assumed that if the OPT was serving as a plate load choke of sorts (certainly not optimized to anybody's MATH), while also seeing the AC signal coming out of the tube - well if you have a surplus of vintage transformers that came out of EL84 based stereo consoles (Grundig, Nordemende), why not use them. These amps have been seeing daily service for over six months with no smoke yet.  


The final version of the monoblocks are not really very similar in topology at all to any of Steve's designs, for example they are pentode connected with a feedback configuration derived from ideas of Alex Kitic.  But other than the lack of extreme bass extension due to the source iron, or the power output and midrange flavour of say, a 300B, they have yet to embarrass themselves.


To borrow from your tagline, on this project, I not only did improvise, but I guess cheated as well.

BTW, let me once again take the opportunity to publically thank Mr John Edward Vaughn for his invaluable assistance and encourgement with my past and current audio projects.  Since I'm located several thousand miles away, it's impractical for me to knock on his door, shake his hand, and buy him a beer;  but on behalf of myself and the numerous other members of this forum to whom I know he's given assistance :

THANKS BIG GUY    ;D  ;D  ;D

[quote author=chevelle  link=1134139974/15#19 date=1134443180]thanks.. I think since Astro wants to drive two SV83's a channel, the EF86 would not be adequate, from reading Eddie's post. Would parallel wiring each 6N1P/6922 be a better option, or just use one input tube and run each side to the output tubes? [/quote]


Perhaps not, the master could say; but it might be time to regroup and ask what is Astro going for?  
Paralleling both the 6N1P and the SV83's, as well as running the  OPT in series might smear the transparency and holographic imaging that distinguishes the "C" and "CS" models.

IIRC the old the old Signature monoblocks had the option to run either 1 2(?) or 3 SV83s in parallel as system power requirement dictates, but that most users preferred the clarity of the single triode.  


If he needs more power, then something like the EL34 monos or Taboo might better serve his system needs.


IIRC Steve used the 6N1P in the former design, but since that model seems to have recently disappeared from the official product line, and he has become far more circumspect in his publication of detailed schematics, particularly for discontinued products,   it's hard to tell exactly what's going was going on inside that  box.  Gee, that seems to parallel the development of new products,  hmm ....  ???  :)  after all  he needs to make a living at this, and we unscrupulous DIY cloners don't  :-/

Of course the Taboo is a fair departure from the earlier Zen topology in several respects, most notably the pentode connection of the output stage, as well as in the use of the 12AX7 driver, and not to mention the complexity of the circuit.

[quote author=chrisby  link=1134139974/15#18 date=1134441870]

BTW, let me once again take the opportunity to publically thank Mr John Edward Vaughn for his invaluable assistance and encourgement with my past and current audio projects.  Since I'm located several thousand miles away, it's impractical for me to knock on his door, shake his hand, and buy him a beer;  but on behalf of myself and the numerous other members of this forum to whom I know he's given assistance :

THANKS BIG GUY    ;D  ;D  ;D [/quote]

Thank you so much for the kind words of thanks, Chris. It's a pleasure to help out when I can, and I value your friendship most dearly. But, ya know I don't drink, and would have to kindly refuse the offer of the beer. I'd sure take you up on an ice cold Pepsi, though. We could even put you up for the night, and take you for a day of sightseeing the next day. We have a futon in my workroom for guests to sleep on, if you don't mind the gentle glow of tubes from the amps burning in on dummy loads! The famous Southern hospitality is on me, if you ever make it to Arkansas.

Eddie

dr_sleep;

my comments re "cloning", etc were very poor attempts at some kind of humor ( I don't yet know what kind)

you're dead right about "stealing" a schematic that is released to the public domain, and also about the cost in materials alone in attempting to duplicate them.

and finally, you're most right of all in describing the joy in listening to a "homebrew" (no matter where the design came from) that makes music like these can do.  

It's more than priceless to plug your pug-ugly little amp(s) into a buddy's $30,000 AudioNote system that might not be well matched to the room, and not embarrassing yourself like an incontinent drunked sailor at the end of a 3-day liberty.

At the risk of repeating myself, IIRC, the former Signature Mono blocks included the option of running any combination of between 1 and 3 SV83's in parallel.

Steve or anyone please correct me on that point

But it's also my recollection that listeners to that amp, and many who have bridged model C or CS (myself included) have noticed an appreciable loss of transparency and "holography" compared to the single tube mode.

You might really want to consider looking at the Taboo circuit, which is quite highly documented, and has all the power available from an EL84/SV83, without the need to parallel tubes.
If 6 watts isn't enough, then you need to consider different output tubes or push pull.


With his characteristic careful voicing and the considerably more elaborate power supply, Steve is confident that he's mitigated the "pentode" penalty, and no doubt many happy Taboo owners would agree.

[quote author=astro  link=1134139974/15#25 date=1134498490]OK guys, thanks again for your comments.

As I mentioned, I'm shooting at different directions right now with my target to get a bit more power than the "regular" Zen SET but with lower costs than building two amps.

I now have an idea, and once again, I'm not an electrician so don't crucify me if my questions are stupid  :) :
I would like to know if it's possible to add to a "regular" Zen (SE84CS for example) another SV83 tube in parallel to each channel. Will I get my 5-6 watts this way while the amp is still SET?
From what I researched I figured out that I would probably have to use 3.3K blue trafo for output and replace the power trafo with a "bigger" one. Hammond have this 372JX model (I need 240v as I'm not from the US) which provides 250ma. Will it be enough considering the "regular" Zen uses less than 150ma?
Once I replace the trafos, all I need to do is hook up two more SV83s in parallel and voilla... a 5-6 watts Zen!

Am I guessing wrong?

Astro [/quote]


It probably wouldn't hurt either sonically or electrically to relieve the total current draw on the mains transformer by using a separate filament transformer for the signal and output tubes.

Don't forget that the majority of the current draw heating your power transformer is from the filament heaters themselves.  
A single SV83 is 760ma, the 6N1p a whopping 600ma (12AX7 as in the Taboo is half that at 300ma) and the rectifiers, while on a separate voltage tap,  either 2 or 3A (5Y3 and 5U4GT respectively).  It's nice to run the amp at an optimum temperature, but you don't want a thermonuclear event either.  A smoking power transformer can be a very stinky, expensive and dangerous thing.

My first 2 junkyard (excuse me, frugalphile) amp projects included recycled iron from European amps that used the EZ81 rectifier, so there was no 5V tap on the mains transformer.  As a result the total current draw on the 6.3V tap was on the wrong side of smart.  It was far easier to use a cheap RadioShack filament transformer (6.3-0-6.3v 3A - all of $14 Cdn)
Including the power supply and parafeed chokes, there is a total of 5 pieces of iron per channel in these monoblocks ( 3 of them recycled - better in my amp than a land-fill somewhere )