atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Can anyone tell me why...

Can anyone tell me why I would get an extreme amount of hum/noise on my non-1A2 telephones if I have one of the 2565's off hook when picking up a "standard" single line phone?

All the 1A2 keysets are 2565 desk models, with the exception of one cuckoo clock.

The "standard" phones consist of a wall mount rotary, a wall mount trimline, and a (I really don't know the model on the next one, but it's identical to the one that used to be on the Johnny Carson show, basically a phone in a wooden enclosure). Oh yeah, a payphone also, but unplugging it completely doesn't help either.

None of them (with the exception of the payphone)date past '75 - '76, and the hum is present regardless of which one I pick up - until I put the 2565 back on hook.

Also it happens regardless of which 2565 I first pick up.

All the standard phones are home run and connect to the CO line before the KSU.

My only guess is there is some sort of backfeed when a 1A2 is off hook, and the "standard" phones need to connect after the KSU instead of before it, but I think that's a bad guess.

Is this where a diode block would come in?

TIA for any tips -

Thanks
Matt

Sounds like you're putting battery from a lamp lead to tip and ring when going off hook. Are you using the SLTs switch hook leads for you A A1 control? If you are remove the second pair and see if the hum goes away, I'm sure it will. You will than have to figure what's wired wrong. Could be batt from the A lead control also.

Matt, it sounds like the violet/green, voilet/brown and violet/slate leads from your 2565 set(s) are not insulated from everything.

Hey all -

Got it. My alarm system is leaking voltage into the return T&R. Heard a small hum with the butt set, then measured across T&R and saw .75 to 1.25v.

Took the alarm panel out of the circuit, no more noise, no more volts.

I was having some other problems with it a month or two ago, this just confirms my suspision of a bad board in the alarm panel.

Thanks for the tips!

- Matt

Matt: Glad you found it. Now, let's get back to how you have your single line telephones ("SLT's") wired into your system.

There are two ways, the right way and, you guessed it! the Bell System Way.

The SLT's need to be converted to A-lead control, and they need to be wired into your system, AFTER the line cards, not BEFORE.

This method will ensure that if a key set is used first, then an slt is picked up, then, finally, the key set is put on hook, there will be no false hold condition.

Another advantage will be on an incoming call, if the call is answered by an slt, the system ringing will stop, and the line lamps will go from flashing to steady.

You will need to convert each slt for A-lead control, and then run their wires to the output of the KSU. More than one slt can be wired to the same pairs, by the way. They do not need to be home-runs, if that helps.

Hey, Arthur: I must respectfully disagree, or at least ask for clarification. You certainly have more experience than I do with this stuff.

If an RJ12C is T/R/A/A1 AHEAD of the line card (supposedly to keep ringer load on the line side of it) and an RJ13C is T/R/A/A1 BEHIND the line card for non-ringing devices, like credit card terminals, etc....Wouldn't what you said be contradictory?

Not to mention that a fully-protected line card (e.g: ITT K400-TPL) wouldn't even allow ring voltage to pass to the station side.

As long as anything sharing that line has properly-functioning A leads, I can't see false hold condition being possible.

THIS and THIS are about the only things left that truly address these conditions anymore. In doing a Google search, it is very disturbing to me how many "authorities" give grossly-incorrect RJ information.

Ed, it didn't mention RJ9! Someplace I read a reference that claimed that 4P4C is an RJ9. All I ever called it was handset cord plug/jack.
OOPS, after double checking, it does mention it as 'un-official' designation. I guess I'm semi-vindicated, based on the description.
I guess it's just another case of someone trying to be technical in a field where he should be plowing instead of thinking! John C.

Yeah, it did under the picture. Take a look:

"Left to right, RJ connectors: an eight-pin 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward semblance to the true RJ45), six-pin RJ25 plug, four-pin RJ14 plug (often also used instead of two-pin RJ11), and a four-pin handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9"). The middle two can be plugged into the same standard six-pin jack, pictured."

PICTURE

It seems to me you can't wire a/a1 ahead of the equipment! t/r yes, but you must be behind the card to even get a/a1 no?

You can wire T/R ahead or behind the line card as long as the A/A1 leads are present and that the switch hook contacts make before and break after the ones controlling tip and ring (yellow/brown switch hook leads were used for the A lead closure in the set).

Because the tip and ring of the line passes through a sensitive reed relay on the line card, high ringing current draw on the station side can damage these windings. This would normally be due to a large number of bridged ringers. Also, later fully-protected line cards did not allow ringing voltage to pass through to the station side.

In general, an RJ12 was used ahead of the card for devices that required ringing, like phones, answering machines, etc. An RJ13 was used behind the card for devices that did not require ringing, like dialers, credit card terminals or modems. Regardless, the A/A1 leads were always the same. There are no separate line and station-side A leads.

Well,

Once again I've proven that there is no finite number of times I can be wrong about something.

Nothing wrong with the alarm panel, except my diagnosis.

Moving all the SLT's after the line card cleared the problem. Also made the voice quality on the 2565's better (There used to be an intermittent scratching sound on them).

Many thanks Arthur.... I'll be implementing the A lead control as soon as Mr. $ says OK. Ed previously pointed me to sandman as a source.

Thanks to all -

Matt

Matt -

Depending on the type & age of the phone, it may be possible to convert the set to a lead control without spending any money. Let us know the model# of the sets you want to convert & we'll get you the wiring conversion.

Sam

Hey Sam -

Model #'s.... hmmmmm.

That could be a problem. Here's a description:

1) Standard beige rotary wall phone we all grew up with. It's been retrofitted with a modular receiver cord, and the "slide on" mounting bracket, but the guts are pure 1960's vintage or earlier. Couldn't find a model # on it, but it is stamped "228" on the back. Metal switchhook. Google says model 554.

2) Trimline... old school style with the round buttons, and (I believe) the first generation of modular handset cords. The connectors are about 1" wide by 1/4" tall. 12 button, light bulb illumination, wall mount. If needed I'll pull it down to see if I can find a model #.

3) The payhone. Pushbutton, WE. Has a 2000/2002/2004 Olympics vault cover, but I don't know if it's original. I don't even know where to begin to find the model # on this.

HTH and TIA!

- Matt

Well I know the trimline because we used to have one...big weird clear connector on it...
I would say the wall phone is a 554.

Matt -

On Standard Single Line Sets, when you went on-hook, you opened both Tip & Ring. All you really need to do is open one of them to break the circuit, so "A-Lead Control" requires first making one of those contacts spare and then using it to provide a closure for the A & A1 leads.

I can't speak to the Payphone (having no experience with them). The other two however...

On the Trimline:

Move the Brown Switch hook wire from C to G
Move the Yellow Switch hook wire from L2 to 3

Move one of the Black Ringer wires from 3 to C
Move the other Black Ringer wire from G to C

Move the Red Mounting cord wire from L2 to C
Move the Black Capacitor strap from L2 to L1 The other side goes to A)

Your A-A1 closure (the Black & Yellow of the Line cord) will be between G & 3

On the 554 Wall set:

Move the White switch hook lead from F to C
Move the Brown switch hook lead from C to G

Remove the Red Ringer lead from L2 & the Black ringer lead from G (they can be wired to the common bell from the ksu)

Tip goes to F
Ring goes to L1
A goes to L2
A1 goes to G

Double check these connections. It's probably been 25 or 30 years since I did one of these.

Sam

Sam -

Makes perfect sense, thanks for the breakdown. Will try it out today and let ya know.

Thanks!
Matt

PS

The Buttset has become inde... indespense...indespensa...

I can't do anything without it.

Sam -

I've got most of the trimline done, and A & A1 control is functional (I've not yet connected it to the KSU, but it checks out with my ohmmeter).

One problem though - I couldn't rewire the ringer as instructed - here is what I've got coming from the ringer:

Black - L1
Red - Destination terminal unlabeled, but it's the other end of the capacitor (i.e. the end that does not have the strap on it).
Gray/Red - Unused
Gray - B

There is also some faint noise on the receiver when the switch hook is held down... could this be related to the as of yet undone bell rewiring?

Thanks!
Matt

Matt -

OOPS! A correction on my part. If you remove the capacitor from the circuit you cannot wire the bell across T&R it has to go to a Common Bell connection off the KSU. I'm going to adjust my earlier post.

I'll have to look at the prints to get you the ringer info, but I would think off the top of my head that the Red & Black leads should go right to the B1/R1 leads in the KSU.

Ed - Jump in here at any time and correct me please.

Sam

Thanks Sam...!

I'll wait on the trimline and proceed with the 554. I've got 4 pairs to the trimline, only 3 are used (T/R, L/LG, A/A1)... so if I need to run the bell back to the KSU it won't be a problem. Truth be told I could forego the ringer entirely, as there are only 6 other phones on the same floor.

Another cup of coffee, and off to the 554. Do you think I'll run into the same issue there? I've only 2 pairs for it.

- Matt

Sam -

One other question - one of the lamp feeds goes to "3". Wouldn't using this terminal for A or A1 cause an issue?

One other thing; I have a Melco C-12 for intercom use. One of the leads is labeled as being grounded when off hook. I'm assuming this is only the case if one of the keysets is off hook, not for SLT's... regardless I can't get a ground reading in either case. Just thought I'd throw this out there in the event it could be used to determine off hook.

Thanks -
Matt

Matt -

You can't mix lamp leads and A/A1 on the same terminal. They used to make little holders for the spade leads (when you ran out of terminals), but you could always give them a little twist of wire and then some tape.

The ground off hook was designed for dial access to PA systems (as I recall). You went off hook on the ICM, dialed a number that pulled in a relay that would connect ICM T&R to a WMT1 matching xfrmr that would connect to the input of an amplifier. (we used to switch ground through the ICM and leave one side of the buzzers leaning on battery). The off hook ground held the relay up while you paged. When you hung up, the ground went away, the relay dropped off and was available for the next page.

Sam

And Finally.......

A Lead controls go for $20 and up... I think I can buld this one for less than $5. Gonna give it a shot anyway, seems to be exactly what I need and it's something to do on a rainy Sat.



Image courtesy of Bill Bowden, @

https://ourworld.compuserve.com/homepages/Bill_Bowden/

Thanks Sam, saw your post after my last. I'm gonna go ahead and build this guy, should have some news later this PM. Seems like a clean, inexpesive solution.

Matt, Put a 200V Full wave Bridge rectifier in the phone line leads before the 3.3 meg resistors on the phone line leads. Then when SWB reverses polarity, it will still work, and you don't have to check polarity when you hook up the circuit! It is possible that the additional resistance the FWB introduces will require that you reduce the 3.3 Meg resistors to 3.0 Meg. John C.

Beware the non-telephone company versions of A-lead control devices. Most are simple series relays, and geared toward phones with tone dialing. They are seldom engineered adequately to prevent relay chattering (and therefore lamp flickering) during pulse dialing.

You could also replace each of your 400-type line cards with a Melco M-487 if you can find them. They allow a single-line set to be wired to the output T & R and the KTU detects when the set goes off-hook. I'm sure Geraldo...er...Ed...has a few in his vault. I have two, but I'm hoarding them for my museum display. They originally cost over 200 bucks, as I recall, and could only be special-ordered by the boss.

I prefer using the A-lead conversion, though, because you can install an eentsy N/C pushbutton on the front of the 554 housing in series with the A-lead, and by pushing the button as you hang up, you can put the line on Hold, allowing you to take the call on one of the 2565's.

Wow, I do have the Teltone version of that card. I never even thought of that! Thanks, Arthur!

Well,

It WAS working just great, but I couldn't leave well enough alone. Went to tidy up some wires, and well, let's just say MOSFET's don't like it when you reverse the power leads. Made a nice flash though. Up to rat shack tomorrow for a new MOSFET.

Also the cost was a bit inflated as the only way to get a 3.3 Meg resisitor was to buy a bag of 300 misc values, of which I only needed 3. That alone would have been $17. So I opted to "make" a 3.3 Meg, which is why instead of 4 resistors you see 19.. lol - (3 1 Meg + 3 100K) * 3. Plus the one 10K resistor.

Total cost if they had all the parts I needed would have been around $10. I'll probably end up buying a commercial control, but it was a fun project, and it was pretty cool while it lasted.

It's still raining, so now my hobby for the day is now switching from soldering irons to aluminum cans, if ya know what I mean.

Arthur -

One thing, actually I kind of like it, but just wondering if it's "normal". Now that my SLT's are after the card, if an incoming call arrives, and I pick it up on a keyset, then pick up a SLT, then put the keyset back on hook... the line button flashes hold. Once I hang up the SLT, the keyset lamp goes out. Again, I like it, but wondering if maybe I did something wrong.

Thx
Matt

You need your SLT's to have their T/R connected AHEAD of the line card, not behind it.

Otherwise, there MUST be a slight delay between when the A leads open/close as opposed to the T/R switch hook leads. It looks like your circuit design causes the T/R and A lead closures to occur at the same time, which will never work with your SLT's T/R connected on the station side of the line card.

Ed -

That's the way I originaly had it, but if it's setup that way, and a call is picked up on a 2565, then someone else picks up a SLT... they get LOTS of noise until I hang up the 2565. After much checking, double checking, checking your comments (all the leads you listed from the 2565's dead end at the 66 block, with no cross connects, jumpers or clips hooked to them), as well as checking Bills suggestions.... I decided to try putting the SLT's after the card.... noise went away completely, as well as did a scratching sound that has been present on the 2565's.

So I'm a little confused on my next move, mainly because I still don't understand why the noise is present when wired as you describe.....

I'm sure I'll get it figured out eventually.

With a lot of help.

Matt, I must disagree with the folks who keep telling you to put the SLT T&R before the line card. It was never done that way on 1A2 key systems in Bell System territories. Other equipment could use that scheme, but in general practice, it was never done.

In shoebox installations, (551 series KSU's) there was no ringing generator, and small installations had the key sets wired internally for bridged line ringing. This scheme was not detrimental to any line cards that I ever worked on, and I probably worked on several tens of thousands of them in thirty years.

SLT's need to be wired for A-lead control, and wired to the KSU just as if they were one button of a multi-button set. A third pair (T&R and A leads being pair 1 & 2) is for the CMB. There is no reason that the ringer in the phone cannot be wired on the output leads of the 400-D KTU. I have many practices showing exactly that scheme. The WE 400-D ktu, which was the most prevalent one in use, had no problem controlling ringers after the KTU.

For you to understand how this works, and why you're getting weird results, here's the scoop: To put a call on hold, two things happen, and they happen in a particular order. The A-leads open (this happens on the down-stroke of the red Hold button) the line key releases the T&R (this happens on the upstroke of the Hold button, just as it hits bottom, releasing the line key mechanically.) This sequence, which is tightly timed, is done with relays (later IC's) in the line card. The A relay is associated with the T&R and the H relay is associated with the A leads.

Hanging up in a normal manner, whether by releasing a line key, or just hanging up, releases the T&R before the A-leads open. Therefore, no Hold condition. If for some reason the contact (switchhook or line key) sequence gets fouled up, you'll get a false hold.

See more discussion below about false hold.

This sequence is critical to putting a line on Hold. That's why, in a previous post, I said to install a N/C push button in series with the A leads on your 554 to use as Hold button.

Another admonition: If there are many ringers bridged across the output T&R leads of a 1A2 key system, there is a possibility of a false hold upon hangup. The capacitors of the ringers will essentially cause the A relay to be slow-release, so that by contrast, the A-leads are opening first. This will put the call on Hold. The remedy is to eliminate a few bridged line ringers.

If you try to create a homemade A lead controller, it must behave just like the real thing, meaning that the sequence must be correct.

In the long run, you are better off converting your SLT's to A lead control.

Arthur -

Sam

You can wire T/R ahead or behind the line card...

This is a new one on me. I have always understood the operation of the 400 line card to be open the A/A1 before T/R and the line gets put on hold. Open the T/R before the A/A1 and the line goes on hook.

The logic involves the sequence of two relays on the card, the line sensing relay in series with the CO line and the A-lead relay. If you connect before the card (the CO line directly) the relay in series with the line will not operate when the T/R opens and closes on the hookswitch. I can't see that doing anything other than a false hold.

-Hal

Just remember that an SLT device will not be placing a call on hold, only keysets will be placing calls on hold. For this reason, only keysets need to have their T/R connected behind the line card. A combination of off-hook current flow sensed on the station side T/R plus the A-lead going open is what causes the line to go on hold.

Current flow on the station side is ONLY needed for this purpose. SLT devices need not be drawing current through the station side because they have no means to open the A lead simultaneously while in use.

Then, we need to refer back to the potential for bridged ringer load affecting the line card's reed relay's current limitation.

Western Electric's 400H line cards were designed to address this argument (among other things). Any device going off-hook on the station side T/R without A leads present will immediately result in an on-hold condition when using this card.

Funny, that's exactly where I learned this, from New Jersey Bell, NY Telephone and C&P Telephone installation practices in the mid 1970's through the 80's.

Also, many brands of line cards included polarity guard for the station side (Some San/Bar, Brand/Rex and ITT400TPL and WE400H). Ringing voltage on the station side would be unavailable. This was an FCC thing to prevent DIY's from getting shocked with consumer-level 1A2 system sold over the counter. Yes, there were phone stores that sold 1A2 systems and San/Bar made them, designed for DIY use. Sales of these required fully-protected line cards where the T&R were electrically isolated from ring voltage and the line's 48VDC.

If I am so far off the mark, I urge anyone here to explain the difference between an RJ12 and RJ13 connection. I'm fairly confident that you will find that I am correct.

I have printed documentation if anyone is interested in a fax. I don't have it stored in a format where I can e-mail it.

Well, if I contribute nothing else... I sure am good at starting lively discussions!

Regardless of how I end up finishing this thing off, I'm really enjoying this debate.

PS

The homemade A1 control is working perfectly... Well, except for the false hold condition, but that is nothing to do with the A1 control.

And anyway I like the flashing light....

Basically everythig is working how I want.... I'll sit back now and watch the debate about how things should be wired......

In any event, Thanks for all the discussion!

Ok, I see what you are getting at. If you think about it I answered my own question.

Open the T/R before the A/A1 and the line goes on hook.

If you put a SLT T/R before the card the T/R after the card will ALWAYS be open regardless of whether the phone is on or of hook, won't it? So the A/A1 will ALWAYS open AFTER the T/R because it is always open.

-Hal

I agree that converting the SLT's to A lead control is the way to go.

The disadvantage in my mind is I can't do it to every SLT I own, for example, the pay phone. Plus if I add another SLT, I have to go through the rewire process again, which isn't that big of a deal, but I tend to like to keep things configured as they were when they left the factory.

I gotta say It's very satisfying to just plug in an SLT, pick up the receiver and watch my 2565's light up.

I'm pretty much sold on how I have it setup, but the "before or after line card debate" has my interest.

Things sure seem to work better by putting it all after the line card, but I can see why this could cause problems for the cards. I have about 8 spare K400E cards if I should end up toasting one.

Having said all this, until I can figure out the noise that is present when wiring SLT's before the cards... I'm opting to leave everything after the card.

And now, in the red corner with blue trunks... Ed...

In the green corner, with red trunks... Arthur...

Have a clean debate and no hitting below the belt....

We always did it the way Arthur said: All Telephone set T&R, whether Key or SLT, were cut down (with their A Leads of course)on the output of the card.

I have used 6Bs & Melcos for a variety of circumstances where a lead conversion was not possible (modems and fax machines especially). Never had a problem with them.


Matt, when you have all this A-Lead stuff mastered, there is another challenge for you -the ultimate uber-Alead application, that which struck fear into the hearts of telephone men everywhere for a generation (maybe two):

The dreaded REMOTE HOLD.

I can say no more. It's too frightening just to think of it.

Sam

Matt:

I'll just concede on this one. I lack the experience to continue the debate. If you would like me to fax the docs on the differences, I'll be happy to do so. Just PM me a fax number.

Well, down but not out. The card I made is apparently closing A/A1 before T&R make it. So... hold doesn't work.

I'll be getting one of sandman's devices one day. But for now, I just wired my homemade circuit to A/A1 of line 3; so if the line 3 is lit, line 1 is in use. Not perfect, but hey, I need to find a use for all the extra keyset bulbs anyway.

The saga will continue, I'm sure....

Meantime I've learned one heck of a lot about how the cards function. Thanks everyone for your comments and tips.

- Matt

I've been reading these posts pretty much every time I see something new. It's very interesting and I'm learning a lot too!

Too bad it's all for naught. 1A2 WAS an interesting system that is bullet-proof, but finding 1 in operation is pretty much astounding, these days. Well, at least in a commercial application. John C.

John -

Based on your comments about adding a bridge rectifier, can I assume you have some knowledge of circuit design?

I need a way to introduce an adjustable delay between the time my homemade A lead control (MHALC) senses T&R current and the time it closes the relay contacts.

Just curious...

Thx
Matt

REMOTE HOLD!!! Arrrrgh!

Remote hold using 1A1 or 1A2 was bad enough (before the advent of the SanBar card or the Teltone 487)

Try installing remote hold using 1A equipment with flashing line lamps, if you want a challenge that will make your gums bleed. I did it once, and have never been the same since.

What is remote hold? I didn't want to send Sam over the edge, so I didn't ask before...

But now I must know.....

Oh yeah - one other advantage with my kludgy A1 control - I can tell if someone is talking on an SLT or a keyset. W00t!

Matt, Closes the relay contacts, or Opens the relay contacts? John C.

Closes - It's N/O till it senses current on T & R.

Hey John -

Was walking the dog and it occured to me what you were really asking.

I think what's happening is that the relay is closing before T&R are established; if I've read the replies here properly it has to go T&R followed very closely by A/A1.

So I was thinking I need an adjustable delay between the time the circuit detects T&R and then closes the relay.

I'm probably worng though.... I'm pretty good at that.

Thanks
Matt

The A leads must close before the Tip and Ring contacts when going off-hook. The A leads must open AFTER the tip and ring contacts when going on-hook.

Oh. Well, I knew I'd get it wrong - thanks Ed!!

Gives me an idea....

Matt, I don't know how well this is going to work without breadboarding it, but. An electrolytic capacitor from gate lead to source lead will slow both turn on and turn off. Value? Start with 10 uf and work your way up. Any voltage from 16 volts on up for voltage rating. The uf value will change the lag for turn on and turn off. Something from 1uf to 100uf. I'd suggest using alligator test leads to expirement. Makes it easier to change capacitors. Positive capacitor lead to gate lead, negative capacitor lead to source lead. It's a mosfet transistor, so even 1uf may be enough. Increasing the uf will increase lag, decreasing the uf will decrease lag. John C.

If the previous method doesnt work, putting the same value(s) across the relay coil will have the same effect, although it may require a whole lot more uf. Again, 16 volts or better for voltage rating. Negative lead to drain, Positive lead to positive 12 volts. FYI, putting + capacitor leads together and - capacitor leads together, causes the uf to add, i. e. 12uf and 22uf = 34uf. John C.

I think the lag on turn off is going to cause a false hold condition. Wish I had a 1A2 set up to play with. Put a buttset, turned on, on the 400 card output for line 1, white blue pair, temporarily short the A control white orange pair to light the lamp. Then remove the short across the white orange pair and I'll bet the line card will go on a false hold. Opening A lead before the talk pair is opened does that. Turning the lamp on slightly before or after T and R close, is insignificant in the real world. But, when you hang up the phone, the A lead has to open first, or within a few microseconds of T and R opening. John C.

Remote Hold as Arthur stated was the great nightmare. God help you if you found that job in your bin in the morning. Management would always give you a reasonable amount of time to do the job.....say 2 hours. It usually wouldn't take you more then....... say 2 weeks. And then it wouldn't always work. Or it might work - for two days and then stop working and then start working again.

As Arthur said: ARRGH!

The job is this-

A customer has two offices across town from each other. He wants the same lines installed on key sets in both buildings. When a call rings in, both keysets ring. That's easy. When a line is picked up in Building A it should go steady in Building B (too). When it's put on hold in Building B it should wink in both places. etc.

This was handled with a half pair per line run between the buildings that was tied to a collection of relays (6B, 17B, 18D) wired in arcane fashion. To fully guarantee productivity a pure white goat was then sacrificed and the blood poured over the ....

Well, not really, but you get the idea.

It was A lead control raised to the "Nth power" It was a nightmare.

Later Sanbar came out with a card that took a full pair between sites and replaced the 400 card at each end. I never used them and don't know if they worked.

A nightmare.

Sam

The Teltone 487 solved the whole problem. It is a very complex circuit (physically it fills all the available volume that a 400-type ktu takes up in a shelf.) It weighs a lot. It has many dip pswitches for setting up all the variables. And best of all, it requires NO extra pairs between DPA's.

I have a couple of them, and I plan to hook them up in my museum which will feature a step-by-step PBX and a lot of 1A, 1A1, and 1A2.

Thanks John - I'll run up to rat shack tomorrow and start the experiment. Doesn't really matter if it works or not, causes false hold, or bursts into flames. Just another thing to play with, I really appreciate the tips. Will let ya know.

Sam - I can't even begin to imagine. These must have been some high $ companies to want, pay for, and even think they really need that sort of thing. I mean.... I can see it being somewhat useful, but jeezy weezy. I wonder how many times it broke because someone else came along and cut and used the line for something else. Also can't even begin to imagine troubleshooting when it broke.

Would have loved to be around for that ride though.

John -

Looks like something across the MOSFET is gonna be the way to go. I found a 100 uf, put it on the mosfet, waited 4 mins... nothin. So, something smaller there.

I had a couple 1000uf's as well, first put 1000uf and then 2000 uf across the relay, no apparent effect, switched right on.

Will let ya know more tomorrow.

...later...

10uf causes engagement after about 15 secs. Gonna have to go lower still..

Thx
Matt

Matt -

I don't know what the tariffs were, but I don't think it was hysterically expensive. The bigger companies usually had PBXs, not key systems. We did some pretty fancy stuff with PBXs, networking them, bouncing calls back and forth, etc.- but that was easy compared with Remote Hold.

Sam

Arthur -

Do you have any specs on that 487? I never heard of it. I'm not talking a schematic - just a circuit description.

TIA,

Sam

Jeez I'm an idiot. Ed already said... "The A leads must close before T&R when going off hook". Adding a delay to the A lead closure isn't going to help. Sometimes I wonder what's wrong with me.

I think I like to tinker too much.

I guess what I really need is a -2 uf cap.

I guess it's off to sandman one day. For now I kinda like having line 3 light up if someone is using an SLT.

Matt, there is also a subject that we have not broached yet...

Station Busy lamps !!!

These are lamps, either free-standing indicators or spare lamps in a tel set, that light when a particular station goes off-hook. The station in question can be a SLT or a key set. A pick up key need not be pressed to activate the lamp. Just the fact that the phone is ROH is sufficient.

The scheme uses the A ground circuit, as it passes through the SWHK contacts of the victim's phone. The A ground in the phone is protected against a sneak path by putting a blocking diode in series with the SWHK and the Hold key A ground lead. Then, an additional A ground goes out from the SWHK through a lead in the mounting cord (usually the Y/Br lead), and is then cross-connected to a lamp which has -24 DC waiting on its other side.

The application for this is generally a secretary who needs to know when a boss's phone is ROH.

ITT used to make a box that would mount on the wall of an office, that had rear-lit numbered discs, one for each honcho in the office. The receptionist could then determine which boss (for instance partners in a law firm) could take the next call.

Cool!

I telecommute, so I'm the boss. Now.... where to get a secretary....

But wouldn't -24v blow the lamp? Also, whats ROH? I'm guessing <something> off hook?

As for the lighted discs.... damn. When I was a kid the refurbed the local bowling alley, including putting in new pin indicator lamps (the boards at the end of the lane that tell ya which pins are still standing). I took one home; would have been perfect for this. I could of mounted it in the living room to tell which station was off hook.

Oh yeah - I also took home one of the score desks - the deal with the overhead score projector. I wanted to also take home a ball return, but the overhead was as far as mom & pop would go.

PS:

Saw this on ebay, might it be related to what you are talking about? It was listed as a western electric device.

Matt,
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But wouldn't -24v blow the lamp? Also, whats ROH? I'm guessing <something> off hook?
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Yes, if the bulb isn't a 24v bulb. ROH = Receiver off hook.


Scrounged part of a bowling alley lane once to build a workbech. HEAVY! For anyone interested the alleys were/are made of maple strips about 3 inches wide, 1/2 inch thick, and 3-5 feet long, ON EDGE. All measurements approximate, this was 30 years ago. Glued and nailed. Destroyed two saw blades cutting the width down to 30" X 8 feet. By the way, as I recall, it took 8 of us to load the original slab of alley in my van and the van sagged! That was Lucky Strike Lanes, about 87th and Wornall Road, Matt. John C.

Ah yes, Lucky Strike...! I always hated to see that place go... one of the coolest neon signs I've ever seen. Come to think of it, most of Waldo was neon (I grew up in that area). The bowling alley we scrounged was @ red bridge. And the CO dumpster dives took place over at Red Bridge/Holmes.

I think you once told me you were from KC - but I didn't realize how close....!

Arthur -

What a memory! I'd completely forgotten about them. I don't think I've installed one in 35 years.

Matt -

BLFs were a stock item in the early '70s. We'd wire a diode into the set and feed the BLF on the receptionist's desk (or wall). The unit could be ordered either -24VDC or 10VAC and it came with a variety of transparent label overlays (depending on which system you might want to use it with) Usually we matched the numbers to the ICM. On a K-10 where the only spare was the Y/O pair we'd use 1 wire for a buzzer and 1 for a blf with a common ground for both.

Sam


Yes that unit which was available in 1,2,3,or 4 lamp models was a standard (small) BLF.

You could only use DC, not AC, for the lamp, because the blocking diode would pass half of any AC on the busy lamp lead, causing the A relay in the line circuit to chatter.

That's why the original BSP called for switching the lamps from 10 volt ones to 24 volt ones, as the most prevalent source of DC was -24 from a typical key system supply.

But, of course, there were resourceful I/R people who quickly figured out how to derive -10 Vdc and then the field hassle of carrying 24 Volt lamps down in the bottom of the tool box was solved.

The 10Vdc was manufactured by putting a full-wave rectifier on the output of a Trimline transformer, (output 6-8 Vac nominal) and grounding the positive side through a forward-biased BMF diode to drop the voltage another 0.7 Volt. On average, it gave slightly more than 10Vdc, but the lamps survived due mainly to the voltage drop across the many feet of 24G IWC through which the lamps were powered.

Arthur, is 'BMF diode' an official description, or a slang expression that described the diode in.. shall we say,.. unsuitable for mixed company language. John C.

Arthur -

As I recall, we used to take a spare switchook lead and feed a ground through it and over to the BLF. We may have used two diodes - one facing the BLF one facing back the other way to prevent backfeed. The BLF lamps sat on 10VAC and were switched on with the ground.

I really can't remember exactly. I hate this getting old stuff. I means it's been more then 30 years - but still! I'm going to have to look at the prints and see if anything jumps out at me,

Sam

BMF = a slang description of which the first word is Big.

Sorry to resurrect a dead horse, but my SLT's are now being fed before the line cards.

Bad A/A1 punchdown was the culprit, as I think someone mentioned way, way, way back.