atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Does anyone have an ITT 601A KSU in use?

Hello -

If anyone has a 601A KSU, I was wondering if you could do me a favor.

I get hum when hooking a telephone across AB/AG.

However, if I hook the phone across the T/R terminals of the intercom, there is no hum.

I understand that normally you have AB for filtered voice, and BB for relays, etc - but the 601 only has AB/AG.

Having said that, the manual says that AB/AG can be used for voice, as well as relays, etc.

Ed is shipping me a power supply to see if that's my problem. However, I'd hate to take the chance that there is something wrong with my KSU that causes power supplies to go bad.

I've also replaced every component on the power supply board that I think could contribute to hum (capacitors and diodes). All that's left is the transformer, and from what I'm guessing a couple voltage regulators. (The voltage holds steady on all AC and DC outputs).

Of course, I'm by no means an electronics wizard; pretty much a parts swapper/hack in that area.

Anyway, if somebody has a 601 in use that you could hook a butt set or the tip and ring of a telephone across AB/AG on, and see if you get hum, I'd appreciate it very much.

Thanks
Matt

Well, there's hum and there's humm. Using a butt set you will detect some low level hum on a 601 power supply directly off the AB AG terminals. It should be low enough (approximately 1 VPP) to be audible across AB AG, however, when the voltage is applied to a card, there are additional filter capacitors that take out the ripple altogether. If you have a scope, check out the level of ripple that you have. It's all power supply. There is nothing else (except a defective card, which I assume you have already eliminated as a possible source of the ripple) that can cause hum in a 601.

Rcaman

Rcaman

Rcaman -

Thanks! I'd call it hummmmmm. It definately sounds like AC is present, it's "talk-overable", but annoying.

I don't have a scope

One thing - the voltage (-24vdc) is present on AB/AG with no line cards (K400E) installed. However I have 5 line cards, have tried each one anyway, to no effect.

I'm positive the intercom card must have the additional filtering you describe, becasue as I said, it's clean and clear across it's tip and ring.

I guess what I'm trying to figure out is if ITT never intended AB/AG to be used (directly) for voice - and that if you wanted to do that, then you would have to buy thier intercom card.

One thing I never mentioned - the hum is only present on AB/AG - not the CO lines.

Thanks
Matt

The CO line cards do not use the 24 VDC for talk battery. The line cards use the 24 VDC for relay operation. That is why you do not have any hum issues on the CO line cards. The ITT Intercom card does have additional filtering to reduce the ripple for the intercom.

If you want to use the supply for just battery, then I would suggest two 1,000 mfd. 50VDC capacitors connected together with a 100 Ohm 2 Watt resistor between the two electrolytic capacitors connected between the AG (+) and AB (-) terminals. Be careful of the polarity. This should wipe out all the ripple and give you a clean AG and AB.

Connect the positive terminal of capacitor 1 to the AG terminal. Connect the 100 ohm resistor to the same terminal. Connect the other end of the resistor to the positive terminal of capacitor 2. Connect both negative terminals of the capacitors to the AB terminal. Connect the load to the positive terminal of capacitor 2 (AG) and AB (-). The "nominal" ripple voltage on a 601 power supply is between .5 and 1 VPP AC. This setup should knock down as much as 10 VPP AC to less than .1 VPP AC. At that point, hum should not be detectable.

Rcaman

OK -

I did that, but only one 1000 mfd cap and no resistor.

Will give it a shot tonight.

Thanks!!!!
Matt

This needs a "pi" filtering network and what I gave you is a "Pi" RC filter for 60 to 120 Hz. There is math that can be used to determine the exact values of the resistor and capacitor values. What you have here is like using a shotgun to kill a fly. It works...but you can achieve good results if you know exactly what you are trying to filter. A scope or a good RMS VOM is essential.

A LC network is actually more efficient and provides better filtering, however, most people don't have a spare 100 mH choke lying around.

Rcaman

"I get hum when hooking a telephone across AB/AG."

You can't do this.. Intercom line cards are made for this. The trouble is simple. The A battery and A ground are two different applications. The Ag is the
ground in the crkt. Just as the B battery has a ground.

Grounds are not always common.

The AG completes the crkt. A batt B batt .

What you have is A battery then you have unfiltered B battery. Two separate crkts on the power supply. Don't confuse them. An don't make your grounds common when mixing them.


You need to understand that you are working with two different crkts. One is true DC and the other is supper imposed over a DC wave form.

Matt, you will always hear hum on talk battery supplies, because they are unbalanced. When you feed the talk battery through the "A" relay or equivalent of an intercom talk path, the balanced windings of the relay act as a retard coil, and filter out the noise. You are obsessing over squat, and I say that in the nicest possible way. Did you get the 2565HK cord I sent you for Christmas?

lol

Yep! got the xmas present today, just unwrapped it, and now am going to sing Xmas carols. In fact, I think I'll hand out candy canes for Halloween.

THANKS

(PS: Obsessive doesn't even begin to come close, but it's one of the nicer words used to describe me and at least one of my peronalities). It's what happens when you don't have a life.

Just ask Ed!

Someone said The CO line cards do not use the 24 VDC for talk battery. Bullshit they can be used.

If I press a button with 1a2 you would be surprised what I can't make work.