The E 104 has been produced in different variants from the mid-fifties until the sixties, it has found use in maritime communications and in commercial point-to-point communications (press / weather reports), some of the receivers having been exported to France and Belgium have french frontpanel lettering.
A close relative to the E 108 is the VLF - mediumwave receiver E 108 with a similar design.

This receiver is extremely bulky and heavy, it's 555 x 480 x 590 mm wide and in it's desktop cabinet, the receiver has a weight of 86 kg - not a one man lift anymore...
The receiver can be powered from different AC voltages from 110 to 240 V and has a power consumption of 130 Watts with it's 24 tubes and two stabilizers.

The top third of the frontpanel is taken by the linear dial; when you turn the large bandswitch, the dial is rotated up and down. In the higher frequency bands, only the MHz - digits behind tiny windows in the dial are rotated.
In the left lower quadrant of the front panel, you find the rotary controls in three rows: the BFO control with it's +/- 3 kHz range, the crystal calibrator switch and the reception mode selector. In the middle row, you find the control to adjust the level of the line out output and the AGC time selector and in the bottom row the bandwidth selector and the controls for audio and radio frequency (RF Gain) gain.
In the right lower quadrant of the receiver's front panel, you find two measuring instruments: The left can be set as signal strength meter and control instrument for different tube voltages (switch Kontrolle), the right acts as a tuning indicator for FM reception. Below, You find the main tuning knob with a 1:10 fine tuning gear and the rugged bandswitch, sometimes this has to be moved with some efforts, You might have a look at the innards of the receiver and You will understand...

The receiver acts as single conversion receiver with an i.f. of 525 kHz in the low frequency bands below 5,9 MHz, in the high frequency bands, the signal is converted to a first i.f. of 1,1-2,2 MHz, 1,9-4,1 or 3,9-6,1 MHz (according to the selected band) and then to a second intermediate frequency of 525 kHz.
After having passed the I.F. filter bank, the signal is fed to the AM and FM detector, a BFO can be used to receive CW and single sideband signals.

There has been an optional FSK demodulator Fs Tg 127 for the reception of radioteletype signals and a BP 102 single sideband demodulator to match the E 104.

p.s. I'm still looking around for one (or even two) bezels for the frequency dial missing on my receiver...