atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems 2564 Telephone -- 34 or 41 feature?

Yes, I'm still picking up the 1A2 diagrams from time to time and finding more things to try and figure out.

Looking at the diagrams for a 2564 phone, I see an option which the notes indicate as being the "grounding circuit for telephone with 34 or 41 feature."

It's a set of n/o contacts (just labeled "Gnd switch" on the schematic) which appear to have one side grounded back to the KSU via the slate-white wire and the other side connected to the network so as to be on the tip side of whichever line is selected.

So what are the 34 and 41 features? Are they for ground-start lines? Some other signaling function?

Paul, that option was traditionally used for ground start during a power outage on 1A2 that was installed behind a PBX. A trunk would be cut through to a line appearance key and the grounding button was used to start the trunk.

Paul -

Ed, as usual, is on the money. Ground Start Trunking in an emergency. This feature was also commonly used with a Battery-Backed-Up KSU.

The interrupter was changed from the usual 10VAC to a 24VDC model and a special power supply with a rectifier and storage batteries was installed. We changed the 51A lamps to 52A lamps (24V). Ringing was handled by line bells and even ICM was available using DC buzzers.

I put a setup like this in once behind a Northern Electric SG-1. We installed 3 KV's - one for the receptionist, one for the office manager and one for the President of the firm. The trunks were switched over with two mechanical toggle switches. Nobody really believed this newfangled computer controlled PBX would work as well as the old mechanicals (or manuals) and while they really wanted all the features and the ultra modern console (prominently displayed at reception) they wanted backup just in case.


Sam

There was also (one or more) series of Japanese Xbar PBX that used a ground on a trunk-to-extension call to set up a call transfer. Every CV and KV needed to be equipped with the little ground button.

Arthur -

You're right! I'd forgotten about them. OKI Electric, I believe.

Sam

Thanks! What was the usual method of providing the ground switch -- One of the line keys rewired, a separate button fitted on the phone? (I was even wondering at first if this was for ground-start whether the contacts were arranged to close momentarily as one of the line keys was pressed.)

Re the Japanese PBX transfer function, this was also the standard method on all the old PBX systems here at one time (known as earth recall in British G.P.O. terminology). The newer systems from the 1980s onward gradually switched over to flash recall.

Paul -

There was no "usual" method, both were used in my experience. It was obviously cheaper to use a line key - just remove the locking screw (and ALWAYS tape it inside the set, so when you have to convert it back, you could). If you were using the key as a signalling button for a manual intercom, you had to (should) move the A-lead so it picks up ground whether or not the phone was on hook.

We very often added an external button. I no longer remember the part #s, but there was an external mounting bracket and a button that screwed to it. Buttons (and brackets) came in 1, 2, 4 and maybe even 8 (though I don't believe I ever put any of those in) button modules. They were available in matching colors to the phones.

They were made by Suttle as I recall.


Sam

The 551 key was the little outboard button. I forget the # of the bracket. There were 1, 4 and 8 button keys available, and WE made them first. Suttle cloned them.

The usual method on the PBX sets was the small round "civilian" type pushbutton, in a 3/8 inch hole drilled into the housing of the set, at the lower left corner. The buttons had form C contacts, so converting them from "ground-the-line" to "flash-the-line" was accomplished simply by keeping the same button, and moving the wires around in the set.



The button was always installed so that the Tip side was grounded. If the subscriber were to sit at his desk, not using his phone, and absent-mindedly fiddle with the button, grounding the Tip side would not affect anything. If the Ring side were to be grounded, it would be seen as a momentary ROH, and the switch would attempt to set up a call, or trip an incoming ring during the silent interval, and Mr. Sub would not even know that he had missed a call from his bookie. ("Turf Accountant" for our friends who speak that weird style of English.)