GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

19fiftyeight · 29th Oct 2007, 4:17 pm

I have been on to Telephone Lines and they seem not to know about a GPO power supply although they are going to look into it and contact me if they come up with something. Sorry to be a pain but can you give me some further details of your power device so I can appear not to be too ignorant when I take this aspect further. Thanks again....Alec

AndiiT · 29th Oct 2007, 8:49 pm

Hi,
If you are not too bothered about the "correct sounding" ring, a mains transformer from certain models of (scrap) video recorder will have a 40 Volts AC winding which should be adequate to ring the bells "automatically" I have used these in the past to ring telephone instruments, both directly and via a switchboard.

The GPO's ringing converters were self contained units containing an inverter circuit which operated from the 10 (or sometimes -50) volt speech supply.

Ringing converter type 9A, which were used on plansets occasionally crop up on ebay; These may not be powerful enough to be used on larger boards (such as a 10+50) though.

Regards
Andrew

Station X · 29th Oct 2007, 9:12 pm

Do telephone bells work OK on 50 Hz ringing current Andrew? They were designed to work on 25 Hz. 17 Hz for earlier designs of phone.

A planset ringing convertor should be OK for "preserved" switchboards, as it is unlikely that more than one bell will be rung at the same time.

AndiiT · 29th Oct 2007, 9:52 pm

Quote:

Originally Posted by Station X

Do telephone bells work OK on 50 Hz ringing current Andrew? They were designed to work on 25 Hz. 17 Hz for earlier designs of phone.

I haven't had any problems using 50Hz, as mentioned the "ring" doesn't sound quite right though.

As an aside, I have had problems getting my 2+6 PMBX exchange line relays to recognize the ringing current from a BT Minimaster3 - when switched through to an extension or the operators telephone they will ring, but the boards exchange line lamp(s) and buzzer will not respond; I suspect that this is because the Minimaster3 uses mains derived ringing current - with the Minimaster3 on an incoming exchange call the 50 Hz mains derived ringing current is supplied to the phones via a relay switched on and off by the ringing cadence to give the correct sounding ring.

Regards
Andrew

19fiftyeight · 30th Oct 2007, 9:24 pm

Can anyone advise whether a BT ringing generator Type 2A (1994 vintage) would be of use to me for my upright dolls eye switchboard (10plus30) to achieve switch ringing?Thanks in anticipation..Alec

OldGuyGPO · 14th Jan 2008, 2:44 am

I seem to remember seeing 12 volt supplies for these floated across small lead acid batteries (square glass jar types). I think the 12 volt AC supply was through a Selenium bridge Rectifier (the ones with a row of 4? square heat sinks and gun metal grey colour with a threaded fixing at one end) and the battery smoothed out any ripple.

In some cases where mains wasn't available, zinc carbon card-board battery boxes were used with the neat brass screw terminals on the top. The internal cells in the boxes soldered together were a little longer than the D type cells of today, probably the size of the two cells that fitted into the old style push bike front lamp (circa 1960's). Those cells had the flat brass connector at the front and the flat brass connector on the top.

I'm sure part of the routine maintenance to these switch boards was to replace the zinc carbon battery box (1 off) if mains wasn't used. The supply cable had cotton insulated conductors that used to unravel, (or was that in another life?)

29th Oct 2007, 4:17 pm	#21
19fiftyeight Retired Dormant Member Join Date: Oct 2007 Location: Raunds Northants Posts: 4	Re: GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. I have been on to Telephone Lines and they seem not to know about a GPO power supply although they are going to look into it and contact me if they come up with something. Sorry to be a pain but can you give me some further details of your power device so I can appear not to be too ignorant when I take this aspect further. Thanks again....Alec

29th Oct 2007, 8:49 pm	#22
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. Hi, If you are not too bothered about the "correct sounding" ring, a mains transformer from certain models of (scrap) video recorder will have a 40 Volts AC winding which should be adequate to ring the bells "automatically" I have used these in the past to ring telephone instruments, both directly and via a switchboard. The GPO's ringing converters were self contained units containing an inverter circuit which operated from the 10 (or sometimes -50) volt speech supply. Ringing converter type 9A, which were used on plansets occasionally crop up on ebay; These may not be powerful enough to be used on larger boards (such as a 10+50) though. Regards Andrew

29th Oct 2007, 9:12 pm	#23
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. Do telephone bells work OK on 50 Hz ringing current Andrew? They were designed to work on 25 Hz. 17 Hz for earlier designs of phone. A planset ringing convertor should be OK for "preserved" switchboards, as it is unlikely that more than one bell will be rung at the same time. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

30th Oct 2007, 9:24 pm	#25
19fiftyeight Retired Dormant Member Join Date: Oct 2007 Location: Raunds Northants Posts: 4	Re: GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. Can anyone advise whether a BT ringing generator Type 2A (1994 vintage) would be of use to me for my upright dolls eye switchboard (10plus30) to achieve switch ringing?Thanks in anticipation..Alec

14th Jan 2008, 2:44 am	#26
OldGuyGPO Retired Dormant Member Join Date: Jan 2008 Location: Ringwood Posts: 5	Re: GPO 2 + 4 Tabletop Dolls Eye Switchboard Power Supply. I seem to remember seeing 12 volt supplies for these floated across small lead acid batteries (square glass jar types). I think the 12 volt AC supply was through a Selenium bridge Rectifier (the ones with a row of 4? square heat sinks and gun metal grey colour with a threaded fixing at one end) and the battery smoothed out any ripple. In some cases where mains wasn't available, zinc carbon card-board battery boxes were used with the neat brass screw terminals on the top. The internal cells in the boxes soldered together were a little longer than the D type cells of today, probably the size of the two cells that fitted into the old style push bike front lamp (circa 1960's). Those cells had the flat brass connector at the front and the flat brass connector on the top. I'm sure part of the routine maintenance to these switch boards was to replace the zinc carbon battery box (1 off) if mains wasn't used. The supply cable had cotton insulated conductors that used to unravel, (or was that in another life?)