Polski (PL) 
English (United Kingdom) 
Prepared by: Grzegorz Makarewicz (gsmok), contact:
The WL36 tube amplifier is a device that has earned the title of a cult audio amplifier. It appeared in 1997 and was the first Amplifon design offered on our market (its price in 1997 was PLN 2,200). Every Polish audiophile knows it by hearing or seeing it.
The Hard Life of a Tube Amplifier Designer
The amplifier circuit is classic. It is the so-called "Williamson" with EL34 tubes in a push-pull output stage providing 36W of power. The diagram shown is not an exact diagram of the WL36, however, the differences concern only details such as the lack of a potentiometer, etc. An interesting fact, very innovative for the 90s, was the use of toroidal loudspeaker transformers.
Schematic diagram of the amplifier commonly called "Williamson"
Like most tube enthusiasts, I have always wanted to learn the details of this amplifier's construction. I have finally satisfied my curiosity. Below I am attaching a few photos showing this amplifier in all its glory.
The amplifier's construction is really very solid. Photo 1 shows a general view of the amplifier. The image is a bit dark, which is due to the fact that I tried (unfortunately not very successfully) to position the camera so that the flash would not be reflected in the housing. As you can see, the amplifier has a metal construction with tasteful wooden sides, and the box covering the speaker transformers has individual sides. I admit that I don't like it very much - but that is of course a matter of taste.
On the front panel we find two "toggle switches" and two knobs. What exactly they are for has been kept secret - there are no descriptions. After a few attempts, we can discover that the first "toggle" is the power switch, the second is the anode voltage switch, the knob next to it is placed on the gain control potentiometer and the last knob on the right is the switch - the amplifier's input selector. So we do the first switch-on of the amplifier blindly (unless we have some instructions, which unfortunately I do not have). Since there is no indicator of the power on, we click and see if the tubes do not start to light up after some time - this is really very exciting. Since the amplifier has a delayed anode voltage switch-on system, we also have the fun of determining what position the anode voltage switch must be in - during the amplifier's warm-up period (before the delayed anode voltage switch-on system works) we can click the switch without any effect.
Photo 1.
Photo 2, Photo 3 and Photo 4 show how the amplifier looks from the side. Here you can see the aforementioned wooden sides. In the photos they look a bit too red than in reality. You can't see it well, but the finish of the wooden elements is simply perfect. The clear coat is thick and probably has many layers.
Photo 2.
Photo 3.
Photo 4.
The rear of the amplifier housing is equipped with speaker terminals, input terminals, fuse sockets, a mains socket and a grounding socket. Unfortunately, as with the front panel, there are no descriptions of these elements. It should therefore be assumed that the amplifier has speaker outputs matched to two load values, and three stereo signal inputs. Without time-consuming experiments with changing cables, it is not known which inputs correspond to specific positions of the input selector located on the front panel. This is a big minus. What I like is the use of the box in which the speaker transformers are placed to mount the speaker terminals in its rear wall, thanks to which attaching the cables is easy and there is no "squeeze" so often found in other tube amplifiers.
Photo 5.
And here is the view from the bottom. A solid cover screwed to the chassis with 10 sheet metal screws. The fit of the cover and the holes is beyond reproach. The sheet metal screws used are also suitable - they have very wide heads that make it easier to use the screwdriver and at the same time press the cover very firmly to the chassis. When I dismantled the cover, I discovered that since I had screwed it on many years ago, I was probably the first to unscrew it. I will return to sheet metal screws in a moment. In fact, most brand-name tube amplifiers do not use sheet metal screws, but screws or bolts (I keep confusing the names, but I hope everyone knows what I mean). Screws require threaded holes and in order to hold the connected elements firmly, the thickness of the sheet metal into which they are screwed must be sufficiently large. Unfortunately, this condition is usually not met in the chassis of tube amplifiers and even in expensive designs, after a few unscrewing operations, the threads turn and the screws stop holding. Unfortunately, this is a common feature, unless, as in Phast amplifiers, special nuts pressed into the chassis sheet metal are used. In the case of Amplifon, there is no fear of "twisted" threads. The cover has many drilled ventilation holes, which, although they seem a bit clumsy, certainly do their job. The image of solidity is unfortunately spoiled by the feet, which are more suitable for some small and light measuring device, not a heavy amplifier. The justification for using such anemic feet may be the fact that at the time when the amplifier was built, our market for accessories and parts was really very modest.
Photo 6.
Here's another "front-facing" photo, just before the tubes were removed.
Photo 7.
After removing the tubes, the inquisitive observer would discover that the amplifier uses ceramic 9-pin sockets (ECC82 tubes) and ebonite 8-pin sockets (6N8S and EL34 tubes). He would also discover that the machinery used for the mechanical processing was rather crude, as were the holes in the chassis. Although the holes are pseudo-circular, good centricity of the holes and the tube sockets placed under them has been maintained.
Photo 8.
I left what device assemblers like the most until the very end. In Photo 9 to Photo 23 I show how the amplifier was assembled. An approach was used that combined spatial assembly with assembly on printed circuit boards.
Photo 9.
Inside, the dominant element is the toroidal power transformer. Apart from it, there are six strips of glass-epoxy laminate here and there, acting as quasi-printed boards, and one classic printed board, on which the anode voltage delayed switch-on system is mounted.
Photo 10.
Here are two boards that support the assembly of the components of a single-channel amplifier. The upper board, placed near the ECC82 and 6N8S tube sockets, contains the input stage and phase inverter components, while the lower board, placed near the EL34 tube sockets, contains the output stage components. The board layout and assembly of components are well thought out, the solder pads are large, and the components are placed in such a way as to minimize the length of the connections. Since the universal boards used do not have paths, where possible the components are soldered to the same solder pads. The boards are connected to the sockets using wires that at first glance seem to be a bit too long, but that is not the case as anyone who has to service this amplifier will see.
Photo 11.
And here are the identical boards that make up the second channel of the amplifier. As you can see, good quality components were used (polypropylene capacitors, metalized resistors). Supply shortages can be evidenced by the use of a complicated design of the cathode resistors of the output tubes (apparently there were no resistors of the appropriate power and they had to be assembled from several pieces). The installation of electrolytic capacitors, and especially capacitors bypassing the aforementioned cathode resistors (you can't see it clearly in the photos, but they had to be glued to the chassis on one side so that they didn't swing). It's a pity that axial capacitors weren't used - the view would have been much nicer.
Photo 12.
The next photo shows the board for the delayed anode voltage switch-on circuit. In my opinion, it is poorly designed. The hole spacing clearly does not match the size of the resistors used, which are soldered in strange, bent positions. The board gives the impression of being hastily made and visually fits the amplifier's interior like a flower fits a sheepskin coat. It's a shame, because it unnecessarily spoils the overall good impression of the interior.
Photo 13.
It's time for the board with anode voltage rectifiers. The amplifier circuit uses independent bridges for each channel.
Photo 14.
The enlarged photo of the rectifier bridges shows that they could have been mounted a bit more neatly. We are dealing with high voltages here, so the component leads should have been bent with more care, and it certainly wouldn't hurt to put insulating sleeves on them. Despite these comments, the overall assembly is neat and legible.
Photo 15.
The next two photos show a view of the delayed anode voltage switch-on plate from a different angle - the relay is better visible. The other side of the mains transformer is also visible. It is worth noting that the transformer does not have a traditional mounting cover. Its interior is filled with some substance. Nowadays, such "fillings" are often used, but in the 1990s, covers and rubber pads were more popular. Personally, I am an enthusiast of toroids filled in the interior. Overtightening the covers can damage the transformer winding, even if thick pads are used. After some time, the pads additionally harden and begin to crumble.
Photo 16.
The remaining photos are a "repeat of the entertainment". I tried to show as much detail as possible. The photos show individual parts of the interior in different shots allowing for the identification of individual components.
Photo 17.
Photo 18.
Photo 19.
Photo 20.
Photo 21.
Photo 22.
Photo 23.
Time for a little summary.
In short - it's a cool design. As for the listening experience, it sounds cool too, although it may lack some steam in the lowest frequencies (this is of course my subjective assessment).
And here you can find information about the WL 36 amplifier and other designs based on the Williamson amplifier:
- Article "Wzmacniacz lampowy audio", Elektronika Praktyczna 2/1998,
- Article "Wzmacniacz lampowy Amplifon WL36, Radioelektronik 8/1998,
- Article "Wzmacniacz lampowy Amplifon WL36 dla koneserów muzyki", Radioelektronik 8/1998,
- Williamson D.T.N., The Williamson Amplifier, Audio Amateur Publications Inc., 1994,
- Wzmacniacz lampowy, czyli ciężkie życie krajowego konstruktora, description on the internet.
Prepared by: Grzegorz 'gsmok' Makarewicz (originally (C) 2008 TRIODA)