View Full Version : ADSL microfilter + 'Pert' phone problem

Terry Porritt
10-02-2003, 01:02 PM
We have 2 older NZ made STC 'Pert' telephones, and an el cheapo 'made in China' phone from The Warehouse.
The phone jack points were replaced by Telecom a few years ago with 2 wire type.

With Dynalink ADSL Microfilters plugged in there is no ringer working with the Pert phones but the newer 'cheapo' phone rings ok.

[With the STC phones, dialing 137 and replacing the receiver activates a ringer check]

I suppose this may mean we have to get new phones when ADSL arrives. This would be a bit annoying as they otherwise work ok, and the STC Pert phone virtually set a 'standard' against which other imported touch phones were judged 10-15 years ago, as they fully complied with Telecom PTC requirements at that time.

Is anyone else using old STC phones with ADSL?

Maybe Godfather would know about this one?

10-02-2003, 01:48 PM
The filters must add in a little too much resistance for the telephones liking.

I had a similar problem at Grandma's. We had a 20/30m telephone extension cord going out the bathroom window and running through the trees down the back to the granny flat (where Dad lived funnily enough). Some phones would ring in the granny flat other phones wouldn't. Though they'd both work.... you just wouldn't hear them ring.

Terry Porritt
10-02-2003, 02:17 PM
Hmm... you may be right JM, also the old Pert phones were designed for the 3 wire system with the ringer signal on a shunt wire. 2 wire systems have an integral capacitor, the RAL rating has changed a bit too according to this, there is now a RN and a RL rating for number of phones that can be used together:-


I think the answer lies somewhere in this document in the Ringer section, it may mean internally re-wiring the phones.

Goddie seems to be well up on these topics, come in Goddie :)

Graham L
10-02-2003, 02:28 PM
How do the Pert phones work in the 2-wire system? I suppose you could fit old "Master" sockets for them (with the 2 microfarad cap and 470k resistor + gas spaark gap protector).

Or you could wire inside the phone: cap between 2 & 3, resistor between 3 and 5 (BT socket pin numbers. 2 & 5 are the line connections, 3 is the bell wire).

Don't try modifying 2 wire sockets; they seem to have commoned all the IDCs on each side ... 1,2,3 4,5,6 .

10-02-2003, 02:37 PM
well the 2/3 wiring system would make more sense to me.... hadn't though of that before.

Never knew there were two systems back then.

Terry Porritt
10-02-2003, 03:27 PM
I'd never really thought about that before Graham, when the jack points were changed to the 2 wire system the Pert phones just worked ok. Unfortunately I threw away a handful of the old master sockets. which I liberated from DSIR when there was a big revamp of the building and they were going to go down the tip.
They would have been useful for using the gas spark gap devices, DSE dont stock them any more.
I'd sooner modify the phones if that is the way to go, but I suppose that would invalidate the Telepermit.
If you put a scope on the ringer circuit, there can be about 180v or thereabouts developed, so I suppose a 250v/350v rated capacitor would be ok.

The alternative will be to buy new phones, I hate that word "buy" :D

Graham L
10-02-2003, 03:48 PM
The official caps are 250V. (and 1.8 microfarad). The PTCs are online ... and they still have the "proper" circuit.

You might find the Master sockets ... I know that CRC Salvage in Christchurch have them ... so building wreckers everywhere would ahve them. I think they are used with some PABX installations too. But I would modify the phones if they need it. I suspect you might need just an internal link ...

Do these phones have an actual bell? That's what the grunty capacitor is needed to drive. And they put a single cap in the master, to avoid the heavy loading of the caps/bells in multiple extensions across the voice circuit. An electronic ringer doesn't need it ... just uses the 48V DC, and an opto coupler to detect the ringing AC.

Graham L
10-02-2003, 04:09 PM
Section 7 and section 10.4 (http://www.telepermit.co.nz/PTC200X12.html#10.4) of PTC 200 should tell you more than you want to know.

Also, from memory I referred to pin 3 as the ring pin. I was wrong; it's pin 4. I RTFM -- Relied on The Flaming Memory -- and it's becoming more volatile, obviously needs a new battery. :D

Terry Porritt
10-02-2003, 04:47 PM
I think I have found the answer Graham, with you pointing the way :)
PTC280.pdf is a draft standard for public comment for ADSL filters, here is the relevent section:-

(7) It is strongly recommended that a 1.0 mF, 250 Vdc polyester capacitor is
connected between contacts 4 and 5 of the PHONE side BT jack. This provides
ringing to older phone types, still in common use.
(8) Where no ringing capacitor is provided
a) sales literature and packing shall clearly state that “This filter will
require a separate ringing adapter to work correctly with some older
telephones” and shall specify one or more suitable adapters that can be
used; and
• Preferably, the filter supplier should arrange for suitable adapters to be available from all
outlets supplying filters to end-users. Ringing adapters do not require a separate Telepermit.
(b) the filter shall be clearly marked “2-wire only”.
(9) Unless a capacitor is provided, no connection shall be made to contact 4 of
the BT PHONE side jack.

The formatting may not be quite right but you get the gist.

I opened up the Dynalink filter and there is NO 1uF capacitor between pins 5 and 4 for the BT plug, and the case is NOT marked as 2-wire only.

So, the next project is to see if caps can be suitably added to the phones.


10-02-2003, 05:45 PM
Considered trying a splitter instead?

Terry Porritt
10-02-2003, 06:30 PM
Well Biff, Ive bought a filter now, plus one that came with the Dynalink ADSL router. Not too sure, but I'd have thought a splitter would have had a low pass filter in it for the phone same as a line filter. Maybe still have the same problem.

However the mystery deepens even more!!!!!!!!!

Pulled the Pert phone apart and pin 4 of the BT plug is not connected, ie the Pert phone is a 2 wire device, so why there is no ringer with the filter attached is still a mystery. It does have an earth connection on pin 3 though, odd. Thought I'd cracked it.

Maybe have to get new phones.

Terry Porritt
11-02-2003, 06:41 AM
Yippee, the ringer problem with Pert phones is solved :)

PTC 200 section 10.2 says pin 6 of a BT plug is next to the latch, now either this is in error, or there is a wire reversal, or I have a vision reversal, because what I thought were pins 2 and 3 must be pins 5 and 4.
Connecting a 1uF between 5 and 4 (as recommended in the ADSL filter PTC 280 )works, now I have ringer with the phones plugged into filters.

Thanks for the help Graham.

Graham L
11-02-2003, 02:25 PM
Perhaps my pin numbers were right initially. B-) That would mean that the PTC is wrong. :D In either case it was just a 1:6 reversal.

BTW ... I recently installed Chris Pugmire's fine GLE graphics package on a DX2-66 I've been playing with. DSIR did some good things until they got corporatised and efficiented to death.

Terry Porritt
11-02-2003, 03:50 PM
GLE is a really great program. I dont use it now, but one of the best graphics progs in its day, probably still is.
I think the different packages are still on Simtel.

Graham L
11-02-2003, 04:25 PM
Yes, it's in the msdos/graphics directory on Simtel. I got it first by FTP from the DSIR vax cluster. But the fonts discrepancy is still there. I might see if I can sort it out, one day.