Teleline – Others

Holding Coil

The Holding Coil Unit, Model 7501-40, is used in conjunction with various Teleline Isolator cards for four-wire DX signalling applications (four-wire simplex DC current), as well as for DC simplex powering requirements (i.e., carrier). This type of signalling, also used by certain PBX tie-lines, is fully described in the installation guide.


  • 4-wire DX signalling
  • DC simplex powering


  • The unit provides a means of reintroducing DC voltage across the TX and RX pairs of isolated DX signals
  • The unit is bi-directional and, therefore, the DC voltage source can originate from the Station or CO side
  • The unit can be used to power a two-wire circuit from the Tip & Ring, using an external power supply
7501-40NPMIAA01MAHolding Coil

Plug-in Test Card

The Plug-in Test Card, Model 751366, is a testing device designed for use with the Teleline multi-card shelves. It is not intended to be left permanently installed inside the shelf, and so protrudes two inches beyond the isolation cards to prevent the shelf cover from being closed while the card is inserted.

Test Card


  • The card is used as a lead extension when verifying the continuity of the telephone lines. The card can be inserted into any shelf slot and provides feed-through terminals for Station and Central Office (CO) side Tip and Ring, and CO side Center Tap (CT) equivalence and remote ground
  • Panel jacks are provided for the Station side verification of -24 Vdc, -48 Vdc, Floating 130 Vdc, ring-up generator and station ground
  • The LEDs on the faceplate provide a quick visual check of the power available to the shelf. The LED’s will not illuminate if the polarity of the input power is incorrect
  • In addition to permitting access to “Tip 1” and “Ring 1”, the card also permits access to Tip “A” and Ring “A”. The card-edge connector designation A/1 indicates that the tracks for Tip A or Ring A are on the component side of the double-sided PCB, while Tip 1 and Ring 1 tracks are on the solder side

The card can be housed in the 3-card shelf Model #751127, the 5-card shelf Model #751112/15 (also 751112/1), the 8-card shelf Model #751109/15 (also 751109/13), or in any of our High Voltage Interface (HVI) pre-configured units.

751366NPMIAA01MAPlug-in Test CardUser guide