The Zenith H500, which got the Swiss Army designation E-626, is a quite heavy hollow state multiband radio, the set looks like a black suitcase with a carrying handle, it's dimensions are 43 x 28 x 20 cm.
The receiver can be powered from batteries (which are not available anymore, you would need an anode / B+ high tension battery) or mains. Be very careful before powering up your recently acquired H500: the U.S. version can only be operated from 117 V (mains voltage found in the U.S.), the international version can be operated from 110 or 220 V AC, a voltage dropping resistor is used.

A metal lock at the front unlocks the big lid of the receiver, under the lid, You find the detachable "Wave Magnet".

The speaker grille takes the left third of the front panel. On the right third of the frontpanel, You find the pushbuttons to select the different bands, the receiver covers mediumwaves (BC stands for Broadcast Band), the tropical bands in the 2-4 and 4-8 shortwave ranges and the 31, 25, 19 and 16 m broadcast bands. You find the necessary informations, which shortwave band to use at which time of day, printed on the dial.
In the middle of the frontpanel, You find the round frequency dial. The arrangement of the different bands seems a little bit confusing to me: the broadcast bands are marked red in the 2-4 and 4-8 MHz shortwave bands, the markings for the 16 m band are found between the 2-4 MHz (120-80 m) and the 19 m band dials, the mediumwave frequencies have to be red from the U shaped dial below the 25 m band dial...
The two knobs below the round dial are the volume control and the tuning knob. Four small red sliding switches TREBLE - VOICE - ALTO - BASS are used as tone control, this arrangement called "Radio Organ" can be found on all classic Zenith Trans Oceanic receivers.

The operation scheme of the H500 receiver is not complicated, once you made the first step and applied the correct voltage. As this "Trans Oceanic" is a "grandfather" among the travel shortwave radios, I recommend you to power it from a regulated power supply where You can slowly increase the power over some hours to avoid damages to the capacitors after having checked the radio for faulty capacitors.
The volume control acts as main switch, use the band selector pushbuttons to select the desired shortwave band and look for the corresponding band on the round dial. The dial marks are very coarse, so You have to search for the station and to identify it by the language and a spoken identification or interval signal. The H500 has no BFO for CW and single sideband reception, all these features have been found in commercial communication receivers only in the fifties, when the Trans Oceanic has been constructed.

From the technical point of view, the H500 is a single conversion superhet with one RF preamplifier stage: After the RF amplifier (V1: 1U4), the signal is fed to the mixer stage (V2: 1L6) where the intermediate frequency of 455 kHz is generated. After an I.F. amplifier stage (V3: 1U4), the signal is demodulated, the same valve (V4: 1S5) acts as AF preamplifier, a 3V4 (V5) acts as final AF amplifier.