E-638, Telefunken E 108 Lw/4; developed and produced by Telefunken, Ulm.
The Telefunken E 108 Lw/4 is a very heavy and bulky VLF / mediumwave receiver mainly used for maritime and point-to-point communications constructed in the fifties - a few samples seem to have served with the Swiss Army.
The VLF - mediumwave receiver E 108 covers 10 - 1800 kHz in six ranges and has a very similar design to the Telefunken E104 shortwave receiver.
The 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 75 kg - this will be the reason, many of the receivers have been cleared out.
The receiver can be powered from different AC voltages from 110 to 240 V.
The top third of the frontpanel is taken by the linear dial.
In the left lower quadrant of the front panel, you find rotary controls in three rows: the BFO pitch control with it's +/- 3 kHz range, the crystal calibrator switch and the reception mode selector combined with the mains switch. 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 the signal strength meter which can also be set to display the AF level. Below, You find the main tuning knob (with a coarse and fine tuning speed) and the rugged bandswitch, underneath an antenna switch to change from a long wire and a 60 Ohms coaxial antenna to a DF frame antenna.
The receiver acts as a double conversion receiver with a first I.F. of 80 kHz in the ranges 1, 4 and 5 and 320 kHz in the ranges 2, 3 and 6, the second intermediate frequency is 525 kHz, the same as found in the E104 shortwave receiver.
After having passed the I.F. filter bank, the signal is fed to the AM 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 108.
After two RF preamplifier stages (two EF85), the antenna is mixed with the signal of the first oscillator (EL84) in a ring mixer with the semiconductor diode OA154Q. The first intermediate frequency of 80 kHz (in the ranges 1, 4 and 5) and 320 kHz (in the other ranges) will pass through a six-circuit IF filter, after which it is amplified in an IF amplifier stage (EF85) and fed to the second mixer, here (EF85), it is mixed with the signal of the second oscillator (605 or 845 kHz) to generate the second IF of 525 kHz which is typically found in Telefunken receivers. After two IF amplifier stages (EF85 each), the AGC control voltage is taken from here as well as the signal for controlling two receivers in diversity mode. The second IF is amplified again (ECC81) and demodulated in a germanium diode, for A1 reception here the signal of the BFO is supplied. After to audio frequency preamplifier stages, the signal is fed to the audio power amplifier (EL84), which has an output power of 2 watts.
V1 (EF85, 1st RF preamplifier); V2 (EF85, 2nd RF preamplifier); semiconductor diode OA154Q (ring mixer); V3 (EL84, oscillator); V4 (EF85, 1st IF stage); V5 (EF85, 2nd mixer); V6 (ECC81, 2nd oscillator); V7, V8 (EF85, two IF stages); V9 (EF85, AGC amplifier); V10 (ECC81, AGC amplifier & diversity circuit); V11 (ECC81, IF amplification and BFO); Ge diode (demodulation); V12 (ECC81, NF preamplifier); V13 (EL84, audio power amplifier); V14 (ECC81, calibrator).
Gl (mains rectifier), stabilizer STV150/30 , stabilizer STV85/10.