Hi Martin, as far as the AF output transformer is concerned, you'd be best getting a quote from Ed Dinning for a re-wind because it keeps the set more original and Ed does a fine job. The main reason is that this transformer has a 40 Ohm negative feedback winding as you've noticed, which enables enhancement of some audio frequencies dependent on the volume setting. If you replace this with a bog standard output transformer without a feedback winding the sound quality won't be as good. You could provide a simple form of negative feedback using a resistor and capacitor from the "positive" speaker terminal to the cathode of V3 (EBC33) as shown in the examples here
http://valveradio.net/audio/smart-ne...-feedback.html. However, even then the tone control switching is not going to work properly. If you go that route you'll want to know that you could buy a modern bog standard replacement transformer which is normally available from RS Components
https://uk.rs-online.com/web/p/audio...rmers/2106475/ . Although RS is currently showing it is out of stock on back order, you should find the part number (N35A002F) available from other sources such as Mark Hindes who seems to be showing availablility at £13 + P&P. This transformer is only rated at 3.5W but since you're unlikely to be running the Ekco at full blast it should do the job OK. The data sheet downloadable from the RS website explains the connections because this transformer is a multi-purpose type with different windings for different valve and speaker impedances. An EL33 output valve in Class A has a 7kOhm load impedance and the A23 has a 3 Ohm speaker so you'd need to connect the primary across terminals 1-4 and the speaker secondary across D-B. Hope that helps. Cheers, Jerry