MagneQuest-SethPP2A3-pwr-sm 维修电路原理图.pdf

How to build the Seth PP2A3 Or how I discovered that things are never as simple as planned, especially when writing such a “How-To” thing. By Jean-Francois Lessard ing. Ph.D. Pantheon Audio MagneQuest distributor. (http:/www.pantheon-) Introduction Ive been procrastinating for a looooong time before finally writing this. Say thanks to my dear friend and excellent web designer Mr. Mobile Homeless, AKA Kelly Holsten, (http:/www.i-) and Mike Lafevre, from the MagneQuest fame, (http:/) to have bugged me so I would finally produce what I promised on a drunken evening. Right from the start you should be aware that the goal of this amplifier is to provide a new “simple” tube amp for the newbie in DIY tube audio. I wanted it to be a working platform, from which one can make the design evolve. Hopefully Ill have achieved this goal with the Seth. BTW, why the heck did I called this amplifier Seth? For one, I couldnt resist the pun as I find it as a nice SET flavour in the midrange. Second reason is that in Egyptian mythology, Seth was Horus competitor, The Horus being another design of mine Ive been loving much. Youll notice that the picture quality in this manual could be higher. Due to the large number of pictures, having high resolution pictures would have made for a pretty large file. A CD containing all the pictures contained here but in a higher resolution will be given for free to all those who will have bought the Seth iron package from Pantheon Audio. Boring stuff and other horror stories First and foremost before you jump into this here is the usual disclaimer. If you are clumsy and/or do not know anything about electricity please stay away from playing with tubes circuits and high voltage without learning the basics and being cautious. carelessness may harm or kill you! This article is not intended as a class in electronic so it is your responsibility to learn the safety rules when working with tube circuit. You have to be aware that the way to build the amps that is described here (circuit wiring method, AC wiring, etc.) might definitively not lead to a “UL approved” product. It might end up in a device that will not meet the requirements of the regulations in your area. It is your responsibility to do all the necessary work to make sure the amps will be “legal and safe” to use in your home. Still there? OK lets begin. 2004 Jean-Franois Lessard 1RadioFans.CN 收音机爱 好者资料库Schematic The Seth has a very low part count. It is actually deceptively simple. It is in fact an out of fashion design. No choke loading on the driver stage, no CCS, no bells and whistles. Why? Simply for the newbie to build this amp easily. Does it sound good despite being more or less fashionable? You bet. Have a look at the schematic (note if you cant read a schematic would it be to save your life, I suggest you learn how to. Aint that complicated). The heart of this amp simplicity is L2, the EXO-173 PPS center tapped choke. It acts as the phase splitter in a simple but so elegant way. Putting the choke center tap to ground will create a reflected signal inverted 180o on the bottom leg from the one that is fed on the top leg (where C2 is connected). The rest of the amp is as simple. It is a two stage design where a 6C45-Pi drives a pair of 2A3 in push pull class A. The PSU is a double pi filter, making for a very low ripple. This amp is self biased. The pair of 2A3 shares a single bias resistor so this will ask for closely matched tubes. The list of the parts I used in these amps is given below. Feel free 2RadioFans.CN 收音机爱 好者资料库to experiment with the parts and please do not follow my choices blindly. After all, its your amp your building, not mine. R1 Two Dale metal film 100 ohms 1/4W in parallel R2 Holco metal film 43.5 ohms 1/2W R3 Mills Wirewound 4.02 K 12W R4 Mills Wirewound 12W 1 K in parallel with Mills Wirewound 12W 750 ohm C1 Black Gate FK 100 uF /16 V (optional I did remove it after listening with and without) C2 Solen 3.3 uF/630V C3 Black Gate FK 100 uF/100 V C4 Solen 1.5 uF/630V C5a,b Cerafine 47 uF+47 uF/500 V T1 MagneQuest Peerless S-240-A Ni T2 Hammond 374BX 375V-0-375 V 175 mA T3 Hammond 166Q2 2.5 V CT 6A L1 MagneQuest BCP16 GC Ni L2 MagneQuest EXO-173 PPS Ni L3 Hammond 193H 5 H 200 mA 65 ohms L4 Hammond 193H 5 H 200 mA 6 5ohms 3Building the wood chassis. I always use wood chassis. Ill be pretty vague here since youll find better advises that I could give on the miscellaneous woodworking web sites so Ill skip the details here. In a nutshell I used a copper plate 18 AWG thick measuring 16” by 9” for the top plate. Bottom plate is the same size but in aluminum (utility grade). I will usually oil the chassis with either boiled linseed oil or Tung Oil for finishing the chassis. I usually use a router to do a recess on the top and bottom of the chassis so the plates will rest flush in them. I always use hard woods for my chassis so I can tap 6/32” threaded holes into the wood in order to secure the plates with 6/32” machine screws. I always work with 1” to 1”1/2 thick wood planks (once planed). I cut the wood with a mitre saw according to my top plate size then I glue the four side with a special holding jig to ensure square enclosure will be well square!. You can find those jigs in most hardware stores. Figure 1 illustrates a picture of a chassis drying while being clamped by the jig. Once the chassis as set dry, I round the corners with a router despite a certain Kelly Holsten always giving me shit about it. Figure 1. Drying chassis (no it is not the chassis from the Seth). Figure 2 is a photo of the Seth chassis. Note the recess on the top of the chassis and the tapped holes to secure the top plate. Figure 3 shows a detailed view of the “major holes” to do in the chassis. 4Once the chassis is done and finished, its time to install the components that will go on the side of the chassis and start doing some of the AC wiring. Figures 4 to 8 will show you how. Figure 2. Completed chassis Close up of the recessed hole for the on-off switch, fuse holder installation and hole for the AC socket Figure 3. Detail of the chassis holes. 5 Figure 4 illustrate an overview of the parts location on the internal sides of the chassis. Figures 5 and 6 shows close up of the PSU chokes and the two 2A3 filament transformer installation. I used a “recycled” filament transformer (T3) so I had to make the leads longer. A top view of the location of L3, L4 and T3 fixed on the side of the chassis Figure 4. Location of the chokes and the 2A3s filament transformer Note that the laminations of L3 and L4 are perpendicular to each other. I fixed the chokes with wood screws. Figure 5 Close up of the PSU chokes (L3 and l4 on the schematic of the amp) 6 This is T3, the filament transformer for the 2A3 filaments. It is fixed to the chassis side with wood screws. Since I recycled this transformer from a previous project I had to make the leads longer. You may or may not have enough length in your case. Just make sure to twist the leads from the primary and the secondary Figure 6. Close up of the filament transformer (the blue wire is the secondary center tap) Time to start wiring the AC now. It is important that you understand the method I show here might be illegal in your area. This is your responsibility to make sure your amp is safe and “legal” to use. Most electronic technician will be able to help you on this. I am not. Figures 7 and 8 show the wiring of the fuse and the switch. I install them on the “live” lug of the AC socket (often denoted by a “L” in the socket near the lug). Solder a wire from the on-off switch center pin to one side of the fuse holder. Solder a piece of wire from the other side of the fuse holder to the live (hot) pin of the AC socket. IMPORTANT NOTE: THE WAY OF WIRING THE AC SHOWN HERE MIGHT NOT BE ACCORDING TO YOUR LEGISLATION, CODES, ETC. IT IS YOUR RESPONSIBILITY TO WIRE THE AC ACCORDING TO THE RULES YOU ARE SUBMITTED TO. Figure 7. First step of the AC wiring 7 Solder a piece of wire to one of the two outside pins of the on-off switch. Leave the other end of the wire loose for now. Figure 8. Wiring the on-off switch. Metal work. Here is the part of the amp building process I dont really enjoy. But that is just me About 90% of the amp building time is spent on the chassis (both wood and metal work). I usually start by covering the top plate with masking tape and try out different layout that will be both functional and aesthetic (at least to me). Figure 9 illustrate this process. Once the lay out is figured out I mark the location of the holes to be done and start the punching process. Most holes are small holes for machine screws so they can be done with a power drill. I personally use a small press drill. It goes like a charm. The larger tube socket holes are done with Greenlee punches. I wont recommend any dimension here as it will be up to you to make sure you have the good punch dimension that will fit your tube sockets size. For example, depending of the type of octal tube socket you will get, you will need a 1” or a 1”1/8 punch. Once all the holes are punched, I sand both side of the plate with an orbital sander. Figure 10 shows a finished and punched top plate waiting for the painting or coating or whatever. Ill be honest with you, I dont paint those myself. I have a cat in the house and no matter how careful I am, I always end up with a cat hair or two landing on the wet paint. So I send them to the paint shop instead. Do I hear some of you say “Oh! What a gorgeous copper plate! He should polish them and clear coat them!” Well be my guest and go for it. Expect to spend a huge amount of time polishing these plates! Life is too short in my case. 8 Figure 9. “Honey What do you think of that one?”. Figure 10. Once you are there youll have done 90% of the job. 9Figure 11 shows the mechanical mounting of the parts. The capacitor mounting bracket is a nice gizmo I have made by batch of 20 by a machinist. But it is something you can do yourself easily. This bracket will allow you to install the filtering cap (C5) in a convenient way. Dont bother with figuring out why the stick-on tying pads are already on the copper plate. I cheated and dismantled a perfectly operating Seth to write this “How-to” so they were already installed. See how I like you guys! EXO-173 PPS Ni Rectifier socket 2A3 socket 2A3 socket 6C45-Pi socket CAPACITOR MOUNTING BRACKET BINDING POSTS RCA JACK BCP16GC Ni Figure 11. Internal mechanical mounting of the parts. So where will you punch your tube socket holes? Assuming you want a layout like mine, all the tubes are straight on the centerline according to the long axis of the plate. Assuming that the side of the plate on the rear of the amplifier is the reference point, the rectifier tube is located at 6.25, the first 2A3 is at 9, the second 2A3 is at 11.5 and the driver tube is at 14. I suggest you punch the other holes by locating all the transformers, choke, binding posts, RCA jack in a similar fashion than I did. Mark the holes location and punch them. Sorry not to be more precise but I was too lazy to make a plan. Youll need 3 solder lug strips for each monoblock for building this amp the way I did. Two of these will be single lug strips and one will be a dual lug strip. Make sure the lugs are not of the grounded type. Install them as shown in Figure 12. Done? How about a beer now? 10 Solder lug strip (2 lugs) Solder lug strip (1 lug) Solder lug strip (1 lug) Figure 12 localisation of the solder lug strip. IMPORTANT WARNING: IF YOU ARE A US CITIZEN, DONT DRINK AND SOLDER AT THE SAME TIME BECAUSE THE GENERAL SURGEON WILL KICK YOUR ASS. DRINKING MIGHT IMPAIR YOUR SOLDERING ABILITY. The Belle Gueule Originale was the official beer while building this amplifierFigure 13. Time for a cold one. 11Installing and wiring the power transformer Assuming you punch your holes properly, installing the power transformer (T2 on the schematic) on the copper top plate should be pretty self intuitive. If not please refrain from continuing this project In this article, the Hammond 374BX has been used so everything here is given in reference to it. Figure 14 shows the wiring of the rectifier filament winding and the HT winding from T2 to the rectifier socket. The pinout numbering of an octal socket and the GZ34 are given in Figure 14. Put the center tap of the rectifier filament winding from the Hammond 374BX to pin # 3 of the rectifier socket (do not solder it yet) Twist and solder the rectifier filament winding from the Hammond 374BX to pin # 2 and pin # 8 of the rectifier socket Twist and solder the HT winding from the Hammond 374BX to pin # 4 and pin # 6 of the rectifier socket Figure 14. Wiring of the rectifier socket. Installing and wiring the output transformer Install the S-240-A (T1) on the copper top plate and wire the primary and the secondary windings as shown in Figures 15 and 16. The pinout of the 2A3 is given in Figure 16. The primary center tap of T1 is left loose for now. 12 Solder the secondary of the S-240-A to the binding posts according to your speaker impedance and your S-240A hook up sheet (8 ohm wiring was used here) Figure 15. Wiring the secondary winding of the S-240-A (T1). Solder the blue and the brown wires from the primary of the S-240-A to pin # 2 of each 2A3 sockets. Figure 16. Wiring the secondary winding of the S-240-A (T1). 13 Figure 17. Pin out of the 2A3. Installing the PSU filter capacitor and the ground buss Install the PSU filtering capacitor (C5) and the ground buss as shown in Figures 18 to 22. Make sure the ground buss wont be in the way of the chokes (L3 and L4) and the 2A3s filament transformer (T3) already installed on the side of the wood chassis. Do some “dry fit” trial by placing the wood chassis on the copper plate to see if anything is clear. Mount the dual 47 uF + 47 uF capacitor (C5 a and b) in the holding bracket. OK boys and girls, while Im here please let me introduce to the B+ lug. Just remember where it is Figure 18. Installing C5. 14 Solder the ground buss from the negative lug of C5 to the RCA input jack grounding tab. The mechanical contact between the tab and the chassis copper plate must be good. Figure 19. Overview of the ground buss location. Close up of the ground buss to RCA input jack grounding tab connection. Note the direct contact between the tab and the chassis copper plate (dont use a Teflon insulating wire between the tab and the plate). Figure 20. Detail of the ground buss connection to the RCA input jack. 15 Solder the ground buss to the lug on the single lug strip that is mounted on the front most 2A3 socket. This is only to stiffen the ground buss Figure 21. Detail of the ground buss connection to the stiffening solder lug. Close up on the connection between the ground buss and the negative lug of C5 Figure 22. Detail of the ground buss connection to C5 negative lug. 16Finishing wiring T2 secondary windings Wire the 6.3V winding of T2 as described in Fi