German Television on June 21, 1932!
By 1932, most television development activities in the United States, were now directed towards receivers using a cathode ray tube. This was also true in Great Britain but to a much lesser extent in Germany.
At the 1932 Berlin Radio Exhibition, in addition to radios, there were also displays
and demonstrations of both mechanical and cathode ray tube television receivers.
Telefuken demonstrated two sets, one was a 48 line mirror drum type, equipped with a Kerr Cell providing a 16" X 20" B/W picture. The pictures were judged to be very good, bright and with a slight amount of flicker. They also demonstrated a cathode ray tube set, providing images of 90 lines at 25 images per second. These images had a pale green color, measured 4.8" X 3.6" and were judged to be excellent.
Loewe demonstrated a 90 line cathode ray tube set, operating at 25 pictures per second. The images measured 4.8" X 3.6". In this case, the picture had a distinct blue color. Those who saw it, judged the picture to be very good to excellent.
Fernseh A.G. Their first of three entries was a 120 line at 25 frames per second, disk type receiver equipped with a new type of Sodium lamp. The 2.8" X 3.6" picture produced was a pale yellow color. They used a similar lamp with a 90 line disk type of receiver and it too was operating at 25 frames per second. The picture size on this second set was 6.4" X 4.8" and the picture quality on both was judged to be very good. A third working entry from Fernseh A.G., was a 90 line mirror screw operating at 25 frames per second, with an image size of 6.4" X 4.8". A neon lamp was used to illuminate the screw and the image was pink in color. The image detail was excellent, but the intensity was judged only as good.
There was also a fourth entry shown, but it was not working. It was a 90 line mirror screw exactly like their other, except that it was to be illuminated by a Sodium lamp.
H.H.I. (Heinrich Hertz Institute for Wave Propagation) demonstrated one 90 line mirror screw providing 25 frames per second. They used a new H.F. Mercury/Argon lamp that produced a blue picture measuring 5.2" X 6.0" and judged very good to excellent.
R.P.Z. (German Post Office) They demonstrated one cathode ray type receiver, another disk type with a sodium lamp and and a third using a mirror screw, also with a sodium lamp. All three provided 25 pictures per second. The picture on the cathode ray tube set was blue and it looked to be yellow on the other two. Picture quality on these three sets were judged to be very good.
TeKaDe Demonstrated three different size sets, all with 90 line mirror screws and using Neon lamps for illumination. The smallest set produced a 2.4" X 2.8" picture. The next was 5.2" X 6.0" and the largest was 12.0" X 14.4". All three provided 25 pink colored frames per second and were judged to be good to very good image quality.
There were no television sets offered for sale at the Berlin show for 1932.
Now, let's jump ahead two or three years, 1934-1935.
Problems noted in the 1932 report have for the most part addressed, solutions developed and incorporated. Picture colors are now a good B/W or at least nearly so. Synchronizing has improved and return beam blanking on cathode ray tubes has lead to much improved picture quality. Cathode ray tube life was greatly improved.
With the exception of TeKaDe, all of the potential major television manufacturers have abandoned mechanical scanners of any sort. (It must be pointed out, that TeKaDe also has a major effort ongoing to develop television receivers using cathode ray tubes).
TeKaDe continues to engage in attempts to develop low cost mechanical television receivers and has released these two photos shown here and below, of a model for year 1935.
The photo here shows the complete receiver in its cabinet. It measures about 12 inches square and is about 18 inches deep. The cabinet is all wood except for the glass window on the front, through which one sees the television image. The shipping weight on this receiver is about 25 pounds.
The second photo shows approximately where some of the various significant parts are located. The drawing shows there is a support deck about center from top to bottom and from front to back, with the optical parts located above and the electrical parts mounted below. Since this drawing and its associated comments are written in pencil, it must be assumed that this is not a "released" drawing and that the actual components and their placement may differ from the actual finished or completed item.
The support deck is held in place by six vertical risers, off of the 3/4" base board. Later on, the risers will also support the cabinet cover. The support deck will be installed in such a manner that it can be removed at a later time if desired.
One of the first components to be considered are the motor and the mirror screw. The motor must be a four or six pole synchronous alternating current motor and it is normally supplied with the mirror screw as a package. A synchronous motor is required whenever power line synchronization is used, as is the common practice with mirror screws. The motor will be held in a wooden saddle that will allow the motor body to be manually rotated approximately 90 degrees. This saddle must also allow cooling air to pass from beneath it and into the cooling ports of the motor end plate that mates with air passages in the motor end caps. A metal arm is bolted to the upper end bell of the motor, for the purpose of rotating the motor body a few degrees to align the image start point. Notice in the photo on the left, the motor is held captive by the wood saddle at the bottom and the aluminum clamp at the top. The body is able turn, but with some resistance due to pressure, so as to not be "free to move". In the photo below, the adjustment arm has been added, the small end of which passes through a 2 inch long slot in the side panel of the cabinet.
This photo shows the motor and its phasing capacitor. The motor wires need to be left long enough so as to allow the rotation of the motor body, when setting the position of the image lines starting point. Also notice that the saddle is held in place by 4 screws that pass through the baseplate into 4 "T-nuts"
This photo gives another view of the motor area. The additional wiring seen here is the AC input connector and video and sound input jacks.
The photo above shows the beginnings of the upper support assembly. The front of the finished unit will be on the left and the back is on the right. A clearance hole for the mirror screw has been cut in upper support. The motor is bolted to the 3/4th" thick bottom support member. The mirror screw mounts directly onto the motor shaft and is locked in place with a single set screw.
The photo on the right shows the phasing capacitor for the motor and the AC motor wiring including the AC input connector located on the rear panel. Be sure to include adequate slack in the motor wiring to allow the motor the 90 degrees of motor body rotation. Notice that the original four hole motor mounting is not used, except to pick up a case connection for electrical grounding purposes.
Now we arrive at the present... to examine and consider again, the TeKaDe drawing of the components layout.
The first thing... is the speaker! To "sound right", a speaker must have some sort of baffle. In this case I choose a horn, about which I will explain more later.
The next item I notice near the back, is the mirror screw light source, made up of three items. It begins with a very bright DC powered incandescent lamp, followed by a Kerr cell to provide video modulation and then finally to a matched pair of large cylindrical glass lenses to produce the line of light necessary for the mirror screw.
All of these components, would today be considered very expensive. Instead, I will use a light source that was developed some years ago, using light emitting diodes and acrylic lenses, as described elsewhere on my web site.
A final point is that there appears to be no provision for a motor interrupt switch, conveniently located for the operator. This switch will permit the operator to make course phase adjustments to the mirror screw. This switch needs to be located on the front panel.
The TeKaDe drawing gives no hint about the sound and picture electronics. It would certainly have included a number of vacuum tubes in both the sound and picture sections. And there is also the power supply... supplying the AC for filaments and DC for the plate circuits. Whatever there was... It all had to be located in lower portion of the cabinet, along with the motor. The original TeKaDe design would also have certainly included the necessary RF and detector circuits when the expected signal sources were antenna. Today, those television signals are not available over the air, so the design will be changed to accept both video and sound by cable connection, in the range of .5v to 1.0v P/P. No vacuum tubes will be used in the new design.
As pointed out earlier, something had to be done about the speaker. There was a desire to place the speaker, right in the center front of the cabinet, as is usually the case. This would allow the cabinet to act as the baffle. But here, there was no room for the speaker. A small rectangular speaker next to the viewing port was considered too. This would have required similar grillwork on both sides of the viewing port, to balance out the appearance.
The front panel needed to have three, possibly four sound and video controls plus the motor interrupt switch. This might be a good time to establish just how much room or space will be required for the two amplifiers and the power supply.
What was in mind was to use the solid state audio and video amplifier that had been developed years ago and has used successfully before more than a dozen times. These printed circuit boards are shown here on the right. The audio board on the left is complete in itself. The board in the center is a dual voltage regulated circuit with a separate off-board power transformer. The third board on the right is the video amplifier with circuitry that includes DC restoration for the signal and provides a brightness control for the operator.
It was decided to build an assembly consisting of these three printed circuit boards, the power transformer and three picture and sound controls. The three circuit boards were first mounted on a wood panel, along with the power transformer and the three operator controls. Then a variety of multiple solder type terminal strips were added to facilitate interconnection between these parts.
This photo on the left shows the wood panel with the parts mounted, prior to the actual wiring of the assembly. The transformer is in the upper right and the video amplifier circuit board is just below that. Near the center are three circular shaped components, which are the two video controls (brightness and contrast) and the third is the volume control. Directly above this control is the power supply regulator circuit board and the last item over to the left, is the audio amplifier circuit board. Since the motor interrupt switch was to be mounted on the front panel, there needed to be a means of disconnecting it from the circuits on the board, in the event that service may be required. A connector was later added to this board that mated with a short wiring cable from the interrupt switch.
This is a view of the electronic panel after the various inteconnection are wired in. Notice the small number wires exiting from this assembly. There is a shielded gray wire on the left, from the video amplifier output that will connect to the light source.
On the right there is a 3 conductor line that handles the AC, both in and out and the last cable has 2 shielded conductors, providing the inputs of video and audio signals
With the wiring complete on the electronics assembly, it can be fitted into the horn and support adapter.
A note about the horn construction: The "pink" portion is of a "U" shape, is made from 3 pieces of 1/4" plywood. The wood panel with the electronics, fits into the "U" and is held in place by 2 screws. The horn is permanently attached to the "U" section.
After the electronic assembly is in place, the speaker can be installed into the assembly.
With it all assembled, from another view it looks like this.
This is a view from above and shows the "U" shaped support for the electonic assembly. Notice the two small holes in the front surface. These are for the two screws that will pass through the from the electronics panel and into the front panel. Note that the motor interrupt switch is mounted on the front panel. Only the wire passes through to the electronics panel. When the electronics panel is in place, three control shafts will protrude through the holes.
This is the appearance of the Horn and electronics assembly.
(Without the 3 control shafts poking through)
In the meantime, the front panel, shown in work below on the left, was progressing. In the original photo of the TeKaDe 1935, the glass on the viewing port appears to be held in a vertical position, that could lead to unwanted reflections of roomlight, which may interfere with the television image.
Also, notice the two rectangular sound exit ports, immediately below the viewing port. They are actually located just below the upper mounting surface. Along with the decision to cut those two openings, it was then decided to build the speaker horn that could interface with the front panel and also contain in it, the electronics panel just described.
This photo on the left shows the horn/electrical assembly when it is installed the receiver. It is not necessary to remove the upper deck when installing or removing this assembly.
The PM speaker selected for this project measured approximately 1" by 3" inches with a depth of 2" inches.
There was something said earlier about expensive components in the TeKaDe light source. An excellent alternative is described on my website and it uses a string of high brightness white light emitting diodes in addition to one or two acrylic lenses. A light source of this sort is shown here with one of the side covers removed. When finished, all of the outside surfaces of the light source are painted with a flat black paint. The upper surface of the upper deck is also done in flat black. The round opening below the mirror screw will have a thin section of plywood to reduce the opening size.
The photo on the left is with the cabinet cover off, looking from the back towards the front. The reflecting mirror is barely visible in front of the light source. Notice that everything on the upper deck except the mirror screw and all surfaces are black or flat black. This includes the inner surfaces of the cover.
The reflecting mirror shows up well on this side view as does the cover for the opening in the upper deck for the mirror screw.
This is one of the 3 views of the working completed television.
Notice that the cover is fastened in place by 3 screws in each side. Also notice the motor body adjustment handle, near the rear and about half way up.
This is a rear view of the television. The input video and sound jacks are on the left side, just above the 3 terminal AC input connector.
The working, completed TeKaDe 1935 television.
BY Peter Yanczer (2009)