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jaymanaa 20th April 2006 09:27 PM

Will this work?
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Hey, I need some advice on this schematic. Found it here a couple months ago and getting ready to build it. I'm no engineer, just a solder slinger. The thing that intrigued me was the highish B+ and 10k OPT primary. I tried to do a load line but got totally confused:bawling: . I originally looked at el34 SET designs because I have everything to build one except the OPT's. I was thinking of having some wound for this that would be a little beefier than the se125's he used. I also have a drawing that I did for a power supply to substitute, it would be way more mA than required and I would have to bring the voltage down some, but once again it's stuff thats been laying around that I need to do something with. I'm planning on running this through some Heresy 2's with a CD straight in(Marantz 50 with variable output). I know there are some really good tube guys on this forum and if any of you could see your way clear to help out a fellow tube nut and maybe save me some headaches and heartaches on this one I would be very grateful.

SHiFTY 21st April 2006 09:42 AM

For a SE EL34 this power supply is a little overkill but will work just fine. The current drawn by the two EL34s would probably only require a single 5U4, and this would lower your B+ a bit too.

The caps would need the equalising resistors connected across them, i.e. joined to the junction in the middle. Also you could easily get away with just the one pair of 47uF in series for the first cap.

The choke should be whatever you can get, around 5-10H and rated for 1.5x the current should work ok.

The second cap can be whatever you want, 100uF total would be ok. You probably don't need to use series caps here, but I am guessing this is what you have.

To model your power supply, go to and download the power supply designer (and the tube database!) and plug in the numbers, and adjust to get the smoothest curves.

Good luck!

Tubes4e4 21st April 2006 10:40 AM

Re: Will this work?

Originally posted by jaymanaa
Yeah, that is from my homepage ;)

If you are open to experimentation, I would suggest to try even higher voltage, up to 450V (plate to cathode) for the output stage (while staying within total Pd limits, of course). For Ra, donīt go lower than 10k.

Donīt get fooled by old spec sheets, suggesting lower voltages, higher currents and lower Ra - the objectives were quite different back then (get the most power out of it while using the least iron/copper mass at the same time).

This circuit as shown does magic on voices, choirs, small Jazz combos, chamber music and the like. As I wrote, this one was built to do exactly this. It certainly is no "rocker", though, as a quite similar circuit from the Angela homepage does suggest.

As a side note, this circuit was the first one I really was able to distinguish between different 6SL7 types / brands in blind tests. I wouldnīt have believed until then. A more obtanium alternative to the JAN CHS Sylvania 6SL7 is the cheap and plenty Reflektor 6H9C (6N9S), which sounds better (in this circuit) than many other much more expensive NOS 6SL7 brands, except those old Sylvanias.

Comparatively, the influence of EL34 brand choice is much less audible.


jaymanaa 21st April 2006 11:29 AM

Thanks for the input, I was thinking I could get by with one 5u4, but not really knowing, thought I would error on the side of caution. One will be much handier as the chassis layout is a little crowded. Good point about equalising resistors too. I may use 600v caps as well. I have a bad habit, that if I'm not sure about the designing of something, I just use overkill. I need to work on that. I'm just more at ease with a soldering iron than a pencil:cannotbe: . Hey tubes4e4, It surely is a small world (thanks to the internet). I have many questions. Let me start by saying I really like your circuit (and home page). Very nicely done, and so good of you to share it. You use the term (chamber music). I'm not sure what you mean? I listen to bluegrass and folk, which is all string instruments (no percussion or piano), and for the most part female voice. The one thing I guess that concerns me, is this kind of music uses a very large Bass fiddle instead of drums to keep time. What is your opinion on the low bass capabilities of this circuit? Next, I am curious if you ever experimented with a 6SN7 in place of the 6SL7? I only ask because I have several about. Thank you both again, and please check back from time to time as I am sure I will be needing more advice as this project moves along. I plan to start on the layout this weekend.:) Jay

Johan Potgieter 23rd April 2006 07:40 PM

....and also nice to see a kindly face "attached" to Tubes4e4! (I presume that is you.)


jaymanaa 29th April 2006 02:14 PM

Well, I built the power supply and ended up with 430vdc (no load, but I'm not expecting much sag from this 13# transformer). I also picked up a couple of NOS RCA 6SL7GT's. I'm now getting ready to order the OPT's from Heyboer. I'm specing 10K pri., 120 mA, 15 watts, 4-40khz. (any thoughts before I pull the trigger?). The only thing I'm having trouble finding is the copper to build the chassis. I'm thinking I want 16guage. Anybody know a place to buy sheet copper online? I'm just a little concerned about how the bass response will be if anyone has any thoughts.:scared: Thanks, Jay

jaymanaa 30th April 2006 10:56 PM

Thought I would resurect this, it being Sunday night. I would sure appreciate some advice before I order the OPT's. Surely someone can give an old solder slinger a few words-o-wisdom. Still haven't found a source for sheet copper either:whazzat: Thanks In Advance, Jay

lndm 1st May 2006 02:02 AM

The difference in conductivity for copper and aluminium is not huge and a chassis is often made from a big slab of it. Aluminium may give fewer corrosion issues.

jaymanaa 1st May 2006 09:06 PM


Originally posted by lndm
The difference in conductivity for copper and aluminium is not huge and a chassis is often made from a big slab of it. Aluminium may give fewer corrosion issues.

Thanks, I've pretty much given up on copper for this one. I do have a source for aluminum, however I came across a piece of scrap stainless at work today that is allready bent and welded just a hair larger than I was shooting for. Would stainless be a good enough conductor or would I want to add a copper buss?

lndm 1st May 2006 10:29 PM

Steel is not as good a conductor as copper or aluminium, and by a larger margin. Magnetic fields would also permeate the steel and spread and induce eddy currents (I think). Not sure how successful this would be.

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