if I remeber correctly the remote options were used if you wanted to close a relay to operate some other type of ringing device.
I can't figure out the logic behind the J1 jumper option on the San/Bar schematic (Model 4200A with music-on-hold) at all. Pulling the BR (Bridged Ringing) jumper appears to leave the C.O. tip (pin 14) completely isolated from everything except the holding resistance and MOH circuit; the ringing section of the L relay via its associated rectifier (and blocking capacitor if A.C. ringing option selected) is then just connected across
station side tip and ring. :confused:
Card slots could be equipped with a manual intercom (401A or B) card. This basically provided a simple coupled transformer arrangement to create a talk path. These were used for button/buzzer type intercom systems.
I've browsed through some of the older threads in this section and seen some references to that. Was this just one of the lines to each phone assigned to the internal intercom so that anyone could pick up the intercom by just hitting the appropriate line button?
I also saw mention of a dial intercom card. I'm assuming that this was a similar card which provided not only talk battery for the intercom line but would also recognize DTMF tones (or even pulse?) to sound the appropriate buzzer for the required station.
I note the quite versatile signaling arrangements possible, either a low-voltage audible or conventional A.C. ringing with diode matrix to provide intercom isolation and/or split the ringing for phones not provisioned with all C.O. lines.
The problem is that they required filtered -24VDC "talk or 'A' battery on pins 3 and 18. Since ITT's and San/Bar's cards had music on hold capability through these same pins
Presumably the M jumper to pin 18 on the 400E line card is for MOH. The DR option on the same card appears to apply -24V to pin 3 only when the line is in use/held or ringing (i.e. L relay operated). I'm still trying to work out possibilities for the RU and TU options!
I was told that the reason for this faster cadence was to give employees the perception that the phone line was ringing longer than it really was.
The British Post Office supposedly adopted the double-burst ring {*} which is standard here because it resulted in subscribers answering more quickly. Many PBX systems, and some of the small public exchanges had single-burst ring though, generally where the timing came from an interacting relay set rather than a ringing machine.
{*} Standard cadence is 0.4 on, 0.2 off, 0.4 on, 2 secs. off.
