There are many schematics and many photographs of tubes used later but I cannot find a single photograph of the original apparatus. Even the sketches that were made in the late 19th century are missing important details (like the fact that the electrodes need to be in a vacuum vessel).
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1$\begingroup$ Appleyard's paper on Hertz has some photographs, quality and detail aren't great. Apparently, some original items are kept at the Deutsches Museum in Munich. $\endgroup$– ConifoldCommented Sep 19, 2020 at 22:17
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$\begingroup$ Thank you. You found it! Write it in an answer. Figure 10 in the paper on page 70 is the apparatus used to show the effect of UV light on electric discharge... the photoelectric effect! $\endgroup$– DrFalconCommented Sep 20, 2020 at 6:23
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Appleyard's paper Pioneers of Electrical Communication part 5 – Heinrich Rudolph Hertz (Electrical Communication, 6 (1927) no.2, pp. 63-77) has a number of photographs of Hertz's experimental devices, including the apparatus he used to study the photoelectric effect in 1887 (Hertz did not use the name) after discovering the influence of light on production of sparks in his experiments on reception of electromagnetic waves. A reproduction of the image and the accompanying text are below:
"He observed that the sparks at the gaps of the exploring resonators were influenced by light from any neighbouring sparks - for example, by light from the originating spark at the induction coil. He was in this manner led to discover the influence of ultra-violet light upon electric discharges. The original apparatus employed by Hertz at Karlsruhe to demonstrate this effect is illustrated in Figure 10. A vacuum is first formed in the receiver by an air-pump, and the spark gap is adj u sted so as to be somewhat too long to allow the discharge, with ordinary illumination, to take place. Ultra-violet light, from another spark or from some other source, is then allowed to fall upon the gap, ionization consequently occurs, and the spark passes. Screening of the spark-gap from ultra-violet light consequently diminishes the maximum spark-length in a resonator corresponding to any given arrangement of the resonator. These results were published by him in June, 1887."
Figure 10: Original Apparatus Used by Hertz at
Karlsruhe, to illustrate the effect of ultra-violet light
on electric discharge
