MagneQuest-SethPP2A3-pwr-sm 维修电路原理图.pdf
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1、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
2、 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 shoul
3、d 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?
4、 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
5、 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 ho
6、rror 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
7、! 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 appr
8、oved” 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.
9、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 les
10、s 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 ele
11、gant 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 P
12、SU 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 ple
13、ase 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
14、 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 Mag
15、neQuest 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
16、 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
17、 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 sa
18、w 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 ro
19、und 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 s
20、hows 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 rece
21、ssed 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 transfor
22、mer 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
23、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
24、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
25、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 “liv
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