atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems A-Lead control

I have a cordless phone on my KTS and wanted to be able to get the A-Lead to work on it as it is a 2 wire setup. anyway, I took a 24VDC relay and wired it in series with the ring side of the phone line. when the phone is picked up, I was hoping the relay would engage and make the A lead work, it did'nt. does anyone know how I can make a relay adapter for a cordless phone. Do I need a capacitor in the mix, a lower voltage relay, or something else?? I even tried a regular phone on it and it failed to work... I'm basing my design on the 6B relay from the 1A system... any idea what I need to do?? John

John,

You have the right idea, just the wrong relay. Loop Detection relays are a current sensor relay (not voltage). The relay (if I remember correctly) had a very low voltage coil and was able to accept about a 20ma current flow, which is typical for a 2-wire circuit. Don't forget that this is in series with the cordless base and the base needs most of the off-hook voltage from the KTS 2-wire circuit
Many years ago I built an equivlent circuit using opto isolators to sense the current flow and have it fire a relay.

Another possible thing is if the 2-wire circuit of the KTU has a "B" lead (Busy Lead) you could use that either directly to fire the relay or via a transistor to boost or isolate the current required for the relay coil.

You need an a-lead detector for you SLT. Someone on the board may have one. There are other topics on this, you can use the search feature for this category. Here\'s one.

I know I've still got one or two different types but have no idea where they are. Here's someone who may still sell them:

https://www.sandman.com/

With the proper relay in series with the T&R toward the SLT, you will be able to take the SLT off-hook and operate the A relay in the line card.

However, if you try to retrieve a call that is on HOLD, you will not be able to.

That's because when the line card is on HOLD, there is no line current toward the station, so a series relay will not operate.

If I remember correctly a WE/NE 6B/6C KTU or a Crest A-Lead controller will give you a Busy Lamp indication (go off hook on the SLT and the lamp will light on the Key Set) but if you put the set on hold then going off hook on the SLT it won't break the hold.

WECO made an 18D KTU that would let you break hold. But they were rare even when they were available. I haven't seen one for years.

I should have a 6B/C in the dreaded basement. If you want one PM me. Or try Sandman he may have the more modern type.

Sam

Grab a relay from Sandman https://www.sandman.com/wizard.html#wizard

There's a schematic on the use of the relay for A lead control in the page.

Carl

Arthur, if T & R are 'behind' the KSU, rather than on the 'C.O. side', and A-lead supervision is arranged with a 'Sandman' device or some other A-lead controller, the hold condition will clear, and I suspect you know that and I didn't understand the gist of your last post correctly.

Some people expect to wire the SLT after the KTU, since that is the more logical and easier place to find the T,R,A, and A1 leads.

True, if you wire it ahead of the KTU, it will work.