A Murphy A74 "accessory"... - UK Vintage Radio Repair and Restoration Discussion Forum

Nanozeugma · 16th Jan 2019, 9:02 pm

Hi.
I am in the early stages of investigating a recently acquired Murphy A74.
It appears it has not been "got at"..... except.....

Screwed to the back cover (inside) - many moons ago by the looks - was a small transformer, to which were attached four flying leads in two pairs.

One pair had ancient wander plugs attached, the other pair nothing - bare ends.
None of these were connected to anything inside the receiver.

The rivets to the sets extension speaker socket are sheared, it hangs loose.

Looking at, and reading the resistances of the transformer, it has all the hallmarks of an audio output or LS transformer.
Note that the high current / low resistance winding is not brought out to tags but just wire ends (to which leads had been soldered).
It makes me wonder if it was intended to be bolted to the basket of a loudspeaker and wired direct to the voice coil.

One side of the insulation is marked with a WB logo, I have a feeling I've seen this before, "Stentorian?"

I cannot see any reason why one would need a transformer to connect to an external loudspeaker, as the circuit extract shows, an external LS connects across the output transformer secondary and disconnects the internal LS when plugged in.
The loom to the internal loudspeaker has never been disturbed.

Weird and intriguing. Images attached.

G6Tanuki · 16th Jan 2019, 9:11 pm

Could it have been for "100 Volt line" audio distribution? Low-resistance 'secondary" winding of your extraneous transformer to the original OP-transformer secondary, 100V line connected to the extraneous transformer's high-resistance winding?

julie_m · 16th Jan 2019, 9:35 pm

Could it be a step-up transformer, for connecting an external speaker on a very long cable run with another wired "in reverse" at the far end?

rontech · 17th Jan 2019, 11:00 am

WB I think was a logo for "Whiteley" "Stentorian" loudspeakers. Among my father's items of 1930's radio stuff, was an 8" Stentorian speaker with a similar transformer and multiway selactor switch bolted onto the basket casting.

Nanozeugma · 17th Jan 2019, 11:24 am

Just found this - looks rather familiar...

Ed_Dinning · 17th Jan 2019, 4:00 pm

It could also be to power a tape recorder; boosting the signal and also breaking any hum loops.

Ed

16th Jan 2019, 9:02 pm	#1
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	A Murphy A74 "accessory"... Hi. I am in the early stages of investigating a recently acquired Murphy A74. It appears it has not been "got at"..... except..... Screwed to the back cover (inside) - many moons ago by the looks - was a small transformer, to which were attached four flying leads in two pairs. One pair had ancient wander plugs attached, the other pair nothing - bare ends. None of these were connected to anything inside the receiver. The rivets to the sets extension speaker socket are sheared, it hangs loose. Looking at, and reading the resistances of the transformer, it has all the hallmarks of an audio output or LS transformer. Note that the high current / low resistance winding is not brought out to tags but just wire ends (to which leads had been soldered). It makes me wonder if it was intended to be bolted to the basket of a loudspeaker and wired direct to the voice coil. One side of the insulation is marked with a WB logo, I have a feeling I've seen this before, "Stentorian?" I cannot see any reason why one would need a transformer to connect to an external loudspeaker, as the circuit extract shows, an external LS connects across the output transformer secondary and disconnects the internal LS when plugged in. The loom to the internal loudspeaker has never been disturbed. Weird and intriguing. Images attached. Attached Thumbnails __________________ Thermionic Emission, warms the cockles of your tubes.

16th Jan 2019, 9:11 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: A Murphy A74 "accessory"... Could it have been for "100 Volt line" audio distribution? Low-resistance 'secondary" winding of your extraneous transformer to the original OP-transformer secondary, 100V line connected to the extraneous transformer's high-resistance winding?

16th Jan 2019, 9:35 pm	#3
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: A Murphy A74 "accessory"... Could it be a step-up transformer, for connecting an external speaker on a very long cable run with another wired "in reverse" at the far end? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

17th Jan 2019, 11:00 am	#4
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: A Murphy A74 "accessory"... WB I think was a logo for "Whiteley" "Stentorian" loudspeakers. Among my father's items of 1930's radio stuff, was an 8" Stentorian speaker with a similar transformer and multiway selactor switch bolted onto the basket casting. __________________ Time flies like an arrow, fruit flies like a banana

17th Jan 2019, 11:24 am	#5
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: A Murphy A74 "accessory"... Just found this - looks rather familiar... Attached Thumbnails __________________ Thermionic Emission, warms the cockles of your tubes.

17th Jan 2019, 4:00 pm	#6
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: A Murphy A74 "accessory"... It could also be to power a tape recorder; boosting the signal and also breaking any hum loops. Ed