Page created:

1 August 2023

Current status:  3rd August 2023

We have to thank firstly:


Manfred Schweiger

and their


"Keller Museum" exhibition;

Where we most kindly had been facilitated with the unique opportunity

of taking pictures of their 'Rhodos' apparatus (1943/44).

Thanking them: Very Much!



This brief picture series has been taken out of my "free hand".


Still on holidays in lower Bavaria, I had to use the CorelDraw program version installed on my current Laptop.

This was quite a disappointing experience ! As I am used to operate CorelDraw since, say, 1991; so no-one can say that I am lacking enough experience.

But, some companies apparently hire Children nowadays - and they, sometimes (?), aren't used to understand what their customers are looking for: as, for example, simply: - with a direct mouse clicks changing the colours of lines; such as: a white colour-line body!!

Therefore, I have to apologize for the bordering line nuisances.






E 419 



As they do not possess any kind of documentation - nor any other source of reference; I have used my, say > 60 years of technical experience, in giving a plausible explanation of some of its circuitries.

I might be sometimes "wrong" in my assessments, but my estimates being build upon weighing quite some preliminary: pro and cons.

Thus: all technical explanations and assessments being my responsibility, and -  no-one else's.


Please consider the control-knob designated: 1 .... 11 x 10-7 (left-hand side of the crt display); please consider at the next photograph the long stretched (electrical delay) line with its according "taps".

I have not yet a clear understanding as to how it (all) interacted; however, it is clear that the (Philips) crt type DG 7-2 suffered 'a burning-in' spot-trace.

This happens - when the painted crt spot is being exposed to a too high brightness level for a longer lasting period.

Nowadays hardly understood: but the expression: "screen-saver" was, in the past, just as to prevent such phenomena; think of: TV- or oscilloscope screens.

At least, it tells us - that this device had been operated for, some time, intensively.

I get the impression, that the light-spot damaged the crt screen heavier on the left-hand side than it did towards the centre of the crt screen.


Whether it constituted a prototype apparatus, or that a brief series had been once provided, isn't known to us.



Please consider first the long-resistor like tube.

It constitutes (against the invisible ground-plane) a time delaying device. The visible taps corresponds with the foregoing 1...11 10-7 selector switch.  



The EF 14 was a high-slope valve (tube) and widely used in wide-band HF applications, in Germany and beyond

Considering the quite many valves involved - I tend to suppose that it concerned an AZ 12, as the latter type was designed for increased current applications than an

AZ 11 is capable of.



I have no idea as to how the LS 50 was once operated, in this context. It was capable of operating at quite high voltages (1000..2000 V) as well as capable of coping with considerable currents.

It had a wide-band spectrum application of > 100 MHz.




The (Philips) EC 50 was quite widely employed in continental oscilloscopes as a time-base "gas filled" switching valve; therefore very well fit for time-base purposes.

As we saw a 'burned-in' time-base-line, we may considerable that it was wired as a saw-tooth generator.


Why considering it a Wien-bridge oscillator circuitry?


Considering our first photo, we notice a single range-scale of 1 - 10 kHz.

A ratio of 1:10, and the entire absence of an inductance, I therefore tend to consider that a Wien-Bridge circuitry is most likely; a curiosity is that the gain of such a circuitry necessitates (theoretically) a circuitry " = 3".

In my perception: a tuning range of 1 : 10 would be for an R/C tuned phase-shifting-ladder configuration most unlikely.  




HT rectifier is meant for the DG 7-2 crt circuitry.

In these cases, the deflection circuitry is often kept at an earth/ground like potential and the cathode circuitry is then kept (in contrast) at, say, - 1...2 kV potential.




In my perception: the Rhodos system at least necessitated a signal calibration reference (source)

I consider that they created therefore the:



Type: SJZ 

Impulsfrequenz einstellbar

0,1..1..10 kHz

Impulse width: ca. 5 s


Albeit, that this apparatus could deliver RPF's down to 0,1 kHz.




It isn't always easy to determine why, someone maintained some practice.

No doubt, its circuit simplicity prevailed.



It is simple to notice that someone might have approached this device a long time ago

AOB, a query to myself: I doubt that the transformer on the left-hand side handled the 5s lasting output pulses. 

After all, sadly: I did not take a picture of the full SJZ front panel, and therefore I don't know the accordingly provided signal-output specification; labelled about its coaxial output connector.



By Arthur O. Bauer