"Monitor" refers to the actual model number of this receiver and not a generic function.

Type: 10 tube receiver; single conversion below 3.8 MHz; double conversion from 4.063 to 22.7 MHz;          operates as a TRF receiver on 500 KHz preset. .
Frequency Range: 165 to 235 KHz; 405 to 535 KHz; 1.6 to 2.5 MHz; 2.5. to 3.8 MHz; 4.063 to 4.438 MHz;
6.205-6.525 MHz;. 8.195 to 8.815 MHz; 12.33 to13.2 MHz; 16.47 to 17.36 Mhz and 22 to 22.72 MHz
Red lamp activates during 500 KHz watch.
Power Input: 220 VAC  or 24 VDC
Modes: AM/CW/MCW
Manufactured between: 1966 and 1969
Weight: 16.9 kg (37.25 pounds)
Dimensions in inches: Width 10 3/8, Height 12.3/4 H;  16 3/8 D
Packaging: Available as rackmout or a standalone unit.

Standalone version of the Monitor receiver. This artifact is held by the Marine Museum of British Columbia in Victoria, BC.(Photo by Frank Statham)

Sandy Blaize comments.  "The Marconi “Monitor” was a reserve receiver and was a very improved replacement for the old  Marconi “Alert” receiver which could only tune 500 KHz MCW transmissions. It covered 500 KHz, the 2HHz radiotelephone bands and the 4, 6, 8, 16 and 22 MHz marine bands. However it was a bit drifty on 16 and 22 MHz. but not bad considering the simplicity of the set.  The sensitivity was decent as well.

Marconi made later models of this set that looked completely different and were solid state, but they weren't as good in my opinion.  The Monitor gave the “Sparks” a “complete” package of what he needed. For it’s day, it was a very compact package and a very reliable one at that. "

Spud Roscoe also adds "The Monitor receiver was part of the package that came with the Marconi Globespan transmitter. The Marconi Atlanta was the main receiver with that package. If your station had only the one Marconi Atlanta receiver you  carried the Marconi Monitor reserve receiver. If your station was super deluxe with two Marconi Atlanta main receivers it came with the old Marconi Alert receiver that was fix-tuned to 500 kilohertz or 600 meters"

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Contributors and Credits:
1) http://www.marconi-veterans.org/gallery/main.php?g2_itemId=1171&g2_imageViewsIndex=2
2) Frank Statham  <fstatham(at)telus.net>
3) Spud Roscoe <spud.roscoe(at)ve1bc.com>
4) Sandy Blaize W5TVW <ebjr37(at)charter.net>
5) Shortwave Receivers Past & Present Communications Receivers 1942-1997 by Fred Osterman.

Nov 8/12