Adding external speaker to Wireless set 19 - UK Vintage Radio Repair and Restoration Discussion Forum

Ottawaboy · 22nd Feb 2021, 6:43 pm

Working on a Wireless Set 19 Mark II (Canadian). Anyone had experience(s) adding an external speaker (e.g., connections to output, impedance transformer, etc)? Thanks.

Orakle42 · 23rd Feb 2021, 12:48 pm

Hi

Assuming you want only the A set output from PL2- a Pin 4, drive it into a computer sound system with stereo inputs in parallel - no problem. You will even have an amplifier as well. This assumes the B set & intercom are not required.

PL2-a Pin 4 comes from a tap on the secondary of output transformer T2A which is a low impedance source.

Orakle42

Ottawaboy · 23rd Feb 2021, 2:35 pm

Thanks, that's an option I had not thought of. Yes, only using A set as a receiver.
Thanks again.

G6Tanuki · 23rd Feb 2021, 6:58 pm

In times-past it was Not Unusual [sorry, Tom Jones] for the 6V6 in the WS19's intercom-amplifier to be reworked to serve as an amplifier able to deliver 4 or 5 Watts of audio power: great for listening-on-the-speaker to shortwave broadcast stations on the 41- and 49-Metre bands.

M0SOE_Bruce · 24th Feb 2021, 6:24 am

The output impedance at pin 4 is 100R. It was designed that way to drive multiple headsets. Most speakers are 3-8R so the impedance mismatch will result in lower audio out. By using a matching transformer you'll get best signal. Hammond type 144B is 200R CT to 3.2R so by using 1/2 of primary you'll have a perfect match.

Is the set stand alone or part of a system, ie control box or display?

vosperd · 24th Feb 2021, 8:05 am

On my mk3 ws19 I use an LS3 which is a military loudspeaker with a matching transformer which I believe gives 600 Ohms. This works well.
As I don't have the B set the unused aerial plug has been replaced with a 1/4" jack socket.
I haven't changed the main wiring so I can still use the original headset if I need to.
I have also successfully used a 3 Ohm speaker with a 100V line transformer as used in public address systems, I think these are available.
Don m5aky

Keith · 24th Feb 2021, 10:42 am

I drive the headphones output through a transformer from a defunct Philips domestic valve radio. This had a third winding that was originally used for the negative feedback arrangement. This gives approximately the right impedance match and provides ample volume in a small room from an 8 ohm speaker. I have also used a small mains transformer successfully - we're not looking for hi-fi, after all.

Ottawaboy · 24th Feb 2021, 11:54 am

thanks for the response, I use the set as a receiver only for SW listening, with a mains PS and not a complete set up.

22nd Feb 2021, 6:43 pm	#1
Ottawaboy Diode Join Date: Jan 2021 Location: Ottawa, Ontario, Canada. Posts: 6	Adding external speaker to Wireless set 19 Working on a Wireless Set 19 Mark II (Canadian). Anyone had experience(s) adding an external speaker (e.g., connections to output, impedance transformer, etc)? Thanks.

23rd Feb 2021, 12:48 pm	#2
Orakle42 Pentode Join Date: Nov 2015 Location: Maidstone, Kent, UK. Posts: 113	Re: Adding external speaker to Wireless set 19 Hi Assuming you want only the A set output from PL2- a Pin 4, drive it into a computer sound system with stereo inputs in parallel - no problem. You will even have an amplifier as well. This assumes the B set & intercom are not required. PL2-a Pin 4 comes from a tap on the secondary of output transformer T2A which is a low impedance source. Orakle42

23rd Feb 2021, 2:35 pm	#3
Ottawaboy Diode Join Date: Jan 2021 Location: Ottawa, Ontario, Canada. Posts: 6	Re: Adding external speaker to Wireless set 19 Thanks, that's an option I had not thought of. Yes, only using A set as a receiver. Thanks again.

23rd Feb 2021, 6:58 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 9,815	Re: Adding external speaker to Wireless set 19 In times-past it was Not Unusual [sorry, Tom Jones] for the 6V6 in the WS19's intercom-amplifier to be reworked to serve as an amplifier able to deliver 4 or 5 Watts of audio power: great for listening-on-the-speaker to shortwave broadcast stations on the 41- and 49-Metre bands.

24th Feb 2021, 6:24 am	#5
M0SOE_Bruce Pentode Join Date: May 2013 Location: Deal, Kent, UK. Posts: 118	Re: Adding external speaker to Wireless set 19 The output impedance at pin 4 is 100R. It was designed that way to drive multiple headsets. Most speakers are 3-8R so the impedance mismatch will result in lower audio out. By using a matching transformer you'll get best signal. Hammond type 144B is 200R CT to 3.2R so by using 1/2 of primary you'll have a perfect match. Is the set stand alone or part of a system, ie control box or display?

24th Feb 2021, 8:05 am	#6
vosperd Hexode Join Date: Oct 2007 Location: Bristol, UK. Posts: 367	Re: Adding external speaker to Wireless set 19 On my mk3 ws19 I use an LS3 which is a military loudspeaker with a matching transformer which I believe gives 600 Ohms. This works well. As I don't have the B set the unused aerial plug has been replaced with a 1/4" jack socket. I haven't changed the main wiring so I can still use the original headset if I need to. I have also successfully used a 3 Ohm speaker with a 100V line transformer as used in public address systems, I think these are available. Don m5aky

24th Feb 2021, 10:42 am	#7
Keith Heptode Join Date: Jan 2003 Location: Tewkesbury, Gloucestershire, UK. Posts: 602	Re: Adding external speaker to Wireless set 19 I drive the headphones output through a transformer from a defunct Philips domestic valve radio. This had a third winding that was originally used for the negative feedback arrangement. This gives approximately the right impedance match and provides ample volume in a small room from an 8 ohm speaker. I have also used a small mains transformer successfully - we're not looking for hi-fi, after all. __________________ Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm

24th Feb 2021, 11:54 am	#8
Ottawaboy Diode Join Date: Jan 2021 Location: Ottawa, Ontario, Canada. Posts: 6	Re: Adding external speaker to Wireless set 19 thanks for the response, I use the set as a receiver only for SW listening, with a mains PS and not a complete set up.