Siemens Oscillarzet 05
Hmm. This is something like a German equivalent to the Telequipment S31 having a similar specification and number of tubes (11 + crt and gas voltage stabiliser). On the face of it, it should be superior since it has regulated power supplies and a post deflection acceleration (PDA) tube. Ought to be and it is not. The English design is cunning and effective, the German design is well, something….. and the design falls down in two important areas: 1/ The DG7-74A (3ARP1) PDA crt which ought to be superior does not display frequencies above 1MHz any better than the 3WP1 of the Telequipment (there is a reason that Tektronix chose the 3WP1 for their bottom end scope also), and it suffers from trapezoidal distortion so the Y sensitivity is a little higher at the left than at the right. 2/ The timebase of the German design is a rather poor triggered effort. Rather than using the astable / bistable trigger of the Telequipment, pioneered by Tektronix, it is basically a free running multivibrator type timebase that is set up right on the edge of mono-stable/astable. The result is a tricky and hard to use compromise. It is possible to set it up to transition between triggered and free running using the stability control however, it does not trigger well and tends to synchronise, that is to lock onto integer multiples of the timebase repetition rate, rather than trigger. With very careful adjustment, it is possible to get it to trigger on all ranges; however, because it does not have the free-run trigger multivibrator of the Telequipment, in this state, there will be no baseline, i.e., no trace without a signal present. I measured the bandwidth as 4MHz, decent and good enough to display a 1MHz squarewave. The ability of the timebase to lock gives up at 2MHz. Oddly, the power supply uses a PCL82 and a ECL82 rather than two of one or the other. They have different heater voltages and cannot be interchanged. I guess the reason may have to do with heater/cathode insulation.
Overall, it compares well to the Telequipment S31 however, I prefer the S31.
I obtained the schematic in two parts from Radiomuseum.org. It is very hard to read and the component numbering system is indecipherable to me. Also, the connection from the 150V regulated supply to the timebase is missing completely! I found it necessary to re-draw the time base before I could comprehend it. Here is my sketch, together with a location diagram of the tubes and adjustments on the timebase board. If you are unfortunate enough to possess one of these things, I hope that you find this diagram useful:
The way I found to set it up goes something like this:
Fiddle with the controls until a baseline is present then apply a signal (I use a 10kHz sine wave) and adjust the sweep length (B) until the trace just extends beyond the screen each way.
Set the front panel stability (stabilität) half way,
Iterate with the trigger sensitivity (C) and the stability pre set (A) to get a stable trace.
Now reduce the amplitude to about 1/2 division and play with (A) to get a stable trace.
You may need to continue to iterate between A and C.
Then disconnect the signal and turn the stabilität full CCW.
Locate the stability range adjustment (D) (mounted on the stabilität pot behind the front panel) and adjust it until the baseline disappears.
Re apply the signal and turn the stabilität just clockwise enough to get a stable display. Disconnect the signal, the trace should disappear, turn the stabilität CW and the baseline should appear, turn the stabilität back full CCW.
Re apply the signal and turn the stabilität just CW enough to obtain a stable display. Now play with the signal source frequency, the display should remain locked and the cycles should appear to “pour” in and out of the right hand side, if it does, you have it triggering and so you can view your signal with the sweep vernier at calibrate, no matter what the frequency.
Just to be clear, turning the stabilität CCW should put the timebase into the trigger or monostable state, turning the stabilität CW should put the timebase into the free run or astable state.
If you have a marker generator, use the sweep calibrate shown on the board diagram to set the sweep rate. Do the same for the X5 setting and iterate to get both into adjustment.
Use the X5 centre to get the trace to stay dead centre as you switch X5 on and off. This will take much iteration and patience!
All these adjustments take some experimenting to get a feel for them. I am sure the manual does a far superior job however, I haven’t been able to obtain one and even if I could, I could not read it!
Timebase, trigger and regulator board: