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 +====== E-643: Collins 51S-1 ======
 +**E-643**, **Shortwave Receiver Collins 51S-1**; manufactured by [[Collins|Collins Radio Company, Cedar Rapids, USA]].
 +The venerable [[Collins]] 51S-1, a very compact allwave receiver with a mixed mechanical analog frequency dial, has also been in use with the Swiss Army, probably in the signals intelligence section.
 +{{:​images:​e-643-collins-51s1.jpg?​direct&​600|E-643,​ Collins 51S1}}
 +===== Technical Data =====
 +  * [[Principle]]:​ [[Double conversion|Triple conversion]],​ [[IF]] 14.5-15.5 MHz; 3-2 MHz; 500 kHz
 +  * [[Modes]]: [[A1]] with BFO, [[A3J|SSB (A3JO/U)]], [[A3|AM (A3)]]
 +  * [[Frequency range]]: 0 - 30 MHz
 +  * **Analog dial**, linear analog dial, accuracy better then 1 kHz.
 +  * [[Sensitivity]]:​ Medium wave AM (A3) 15 μV, SSB 3 μV; at 5 MHz AM (A3) <3 μV, SSB <0.6 μV / [[Selectivity ]] (-6 dB): 0.8 kHz; 2.4 kHz, 5 kHz
 +==== Power Supply ====
 +  * [[Mains]]: 115 / 230 V; 85 W
 +==== Dimensions ====
 +  * 375 x 167 x 332 cm, 11.8 kg
 +==== Accessories ====
 +{{:​images:​e-643-collins-51s1-front.jpg?​direct&​600|E-643,​ Collins 51S1}}
 +===== Operation =====
 +The Collins 51S-1 with it's metal cabinet painted in grey is a very compact set compared to the [[E-629|E-629 / 51J-4]] receiver; its dimensions are 37,5 x 16,7 x 33,2 cm and its weight 11,8 kg, - a hollow state double conversion set in such a small cabinet is a suprising bit of engineering.
 +The 51S-1 is prepared to be powered by 115 or 230V AC, the power consumption of the 17 valves is 125W.
 +The different rear connectors make it obvious, that the 51S-1 has its roots among the professional receivers: there are not only connectors for low and high impedance antennas but also for an external VFO, a 500 kHz IF output, and a connector for a long- and mediumwave converter.
 +The front panel gives a very basic first impression: in contrast to several older professional receivers from Collins, the 51S-1 comes with only nine frontpanel controls: The analog dial has an accuracy of better then 1 kHz, the MHz-digit is moved by the MHz-bandswitch and the 0.1 MHz digit is moved by the main tuning knob like an odometer, You hear a click when You go passed a ...99 / ...101 kHz step. You can adjust the zero line of the main dial with the "Zero set"​-knob using the internal crystal calibrator signals or the signal of a frequency standard or time signal after having tuned to zero beat.
 +The mains switch in the left upper corner has a "​Standby"​ setting (in this setting, the valves are heated and frequency stability is reached immediately after switching the set to "​On",​ there is also a position to activate the crystal calibrator.
 +The RF gain and AF gain / volume controles are situated at the left and the right of the main tuning knob. Between this and the AF gain control, you find the modes switch - upper and lower sideband filters can be switched independently - and a control called "​Rejection Tune" slightly above. This activates the Crystal Filter used to notch out unwanted signals.
 +The I.F. bandwidth filters switching is coupled with reception modes: in AM reception a LC or optional a much more expensive 6 kHz mechanical filter is in use, for USB/LSB a 2,4 kHz or an optional 2,75 kHz mechanical filter is switched in the circuit, for CW reception a 800 Hz crystal filter or an optional narrow 200 Hz filter.\\ ​
 +The S-meter in the right upper corner of the front panel can be switched to display the RF or the audio frequency level.
 +To me, it's still unclear in which roles the 51-S1 has been used by Swiss Army branches, but the receiver exists in the inventary of receiving equipment.
 +===== Technical Principle =====
 +{{:​images:​e-643-collins-51s1-block.jpg?​direct&​600|E-643:​ Collings 51S1, Blockschaltbild}}\\ ​
 +The high frequency signal from the antenna input will first pass a bandpass filter and the mechanically coupled automatic preselection stage. In the 0,2 - 2 MHz ranges, the signal is internally up-converted to 28-30 MHz.
 +In the 2 - 7 MHz band segments, the signal will - after the first RF amplification stage - be converted to 14,5-15,5 MHz, in the second mixer to 2 - 3 MHz and in the third mixer to the last IF of 500 kHz - thus triple conversion operation.
 +In the 7 - 30 MHz segments, the signal will be directly converted into 2 - 3 MHz in the first mixer and to 500 kHz IF in the second mixer stage double conversion operation in these ranges.
 +The 500 kHz IF will have to pass the 6 kHz LC filter in AM mode, the mechanical 2,4 kHz USB or LSB filter in SSB mode or the 800 kHz crystal filter in CW mode. After the Q-multiplier circuit with HF notch and two more RF amplification stages, the signal is sent for demodulation to a diode demodulator in AM and a product detector in SSB modes. Two more stages are used for AF amplification.
 +==== Valve setup ====
 +V1 ([[de:​6DC6]],​ RF preamplifier);​ V2 ([[de:​6EA8]],​ 1st mixer, oscillator);​ V3 ([[de:​6EA8]],​ 2nd mixer stage, oscillator 17.5 MHz); V4 ([[de:​6EA8]],​ 3rd mixer stage); V5, V7, V8 ([[de:​6BA6]],​ three IF stages); V6 ([[de:​12AX7]],​ Q-Multiplier);​ V9 ([[de:​6BA6]],​ AGC amplifier); V10 ([[de:​6EA8]],​ LF / mediumwave converter and oscillator);​ V11 ([[de:​5670]],​ AGC decoupling);​ CR1-4 (four 1N34A, product demodulator);​ CR15 (1N34, AM demodulator);​ V12 ([[de:​6BF5]],​ AF output stage, V13 ([[de:​6AK6]],​ AF line output), V14 ([[de:​12AX7]],​ AF preamplifier,​ AF output & line out), V15 ([[de:​7543]] or [[de:​6AU6]],​ VFO), V16 ([[de:​6EA8]],​ VLF converter, calibrator);​ V17 ([[de:​7543]],​ BFO).\\ ​
 +Various rectifiers in the power supply unit.
 +==== Development ====
 +[[Collins]] has developed the 51S-1 in around 1959.
 +==== Field use ====
 +It's still unclear, which was the role assigned to the 51S-1, but seven of this receiver type exist in the inventary of army receiving equipment.
 +==== Variants ====
 +===== Manuals =====
 +==== Additional information ====
 +  * [[http://​​radio-d/​e-643.htm|E-643 / Collins 51S1 auf]]
 +  * [[https://​​r/​collins_51s_1.html|E-643 / Collins 51S1 auf der Website von]]
en/e-643.txt · Zuletzt geändert: 2019/04/07 21:27 von mb