Bush PB12 External Speaker Connection - UK Vintage Radio Repair and Restoration Discussion Forum

BrianAllen · 19th Feb 2020, 6:04 pm

The attached pictures are of the small external speaker panel located at the rear top right of the cabinet (viewed from the rear).

The service sheet says to connect two of the wires from the output transformer; tag 1 to the left hand connection and tag 5 to the right hand connection.

My question is how should this panel be viewed to enable me to make the correct connections?

Thank you.

Graham G3ZVT · 19th Feb 2020, 9:55 pm

looking at the back of the panel as in your second photo, the lead from the transformer secondary that also goes to chassis should go to the left, and the other side of the secondary to the centre.

Removing the screw will mute the internal speaker.

G0HFCFrank · 19th Feb 2020, 9:59 pm

Hi Brian, The purpose of the large screw is to disconnect the internal speaker when an external speaker is in use. Looking at your second picture the secondary of the output transformer should be wired to the two wander sockets (left and centre). A wire from the left hand socket should go to one side of the internal speaker and a wire from the screw connector (right hand) to the other side of the internal speaker. In this configuration the two wander sockets will supply output to an external speaker and the internal can be switched out by loosening the screw. It looks a bit dangerous to me as leaving the screw loose with no external LS connected would damage the output valve. Were it my set I wouldn't bother connecting the panel in.
Frank C.

G0HFCFrank · 19th Feb 2020, 10:01 pm

We almost posted together there but Graham's picture beats my thousand words.

F.

BrianAllen · 19th Feb 2020, 10:11 pm

Thank you gents; just what I needed.

Regards.

Brian

Please close this thread.

19th Feb 2020, 6:04 pm	#1
BrianAllen Heptode Join Date: Nov 2018 Location: Staffordshire Moorlands, UK. Posts: 595	Bush PB12 External Speaker Connection The attached pictures are of the small external speaker panel located at the rear top right of the cabinet (viewed from the rear). The service sheet says to connect two of the wires from the output transformer; tag 1 to the left hand connection and tag 5 to the right hand connection. My question is how should this panel be viewed to enable me to make the correct connections? Thank you. Attached Thumbnails

19th Feb 2020, 9:55 pm	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,724	Re: Bush PB12 External Speaker Connection looking at the back of the panel as in your second photo, the lead from the transformer secondary that also goes to chassis should go to the left, and the other side of the secondary to the centre. Removing the screw will mute the internal speaker. Attached Thumbnails __________________ -- Graham. G3ZVT

19th Feb 2020, 9:59 pm	#3
G0HFCFrank Pentode Join Date: Oct 2011 Location: Oldham, Greater Manchester, UK. Posts: 167	Re: Bush PB12 External Speaker Connection Hi Brian, The purpose of the large screw is to disconnect the internal speaker when an external speaker is in use. Looking at your second picture the secondary of the output transformer should be wired to the two wander sockets (left and centre). A wire from the left hand socket should go to one side of the internal speaker and a wire from the screw connector (right hand) to the other side of the internal speaker. In this configuration the two wander sockets will supply output to an external speaker and the internal can be switched out by loosening the screw. It looks a bit dangerous to me as leaving the screw loose with no external LS connected would damage the output valve. Were it my set I wouldn't bother connecting the panel in. Frank C.

19th Feb 2020, 10:01 pm	#4
G0HFCFrank Pentode Join Date: Oct 2011 Location: Oldham, Greater Manchester, UK. Posts: 167	Re: Bush PB12 External Speaker Connection We almost posted together there but Graham's picture beats my thousand words. F.

19th Feb 2020, 10:11 pm	#5
BrianAllen Heptode Join Date: Nov 2018 Location: Staffordshire Moorlands, UK. Posts: 595	Re: Bush PB12 External Speaker Connection Thank you gents; just what I needed. Regards. Brian Please close this thread.