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Old 18th Sep 2019, 7:45 pm   #1
cornish ekco
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Default Newbie with Ekco A23, advice please

Evening all
My name is Martin from Cornwall
I have inherited from my late father an A23 which I need help on.
I am a vehicle mechanic/vehicle electrician and do vehicle diagnostics so I am familiar with volts resistance etc and a little bit with capacitors.

I think my father bought this radio in the 1960s now and used it now and again until it until the 1980s until it stopped working so has not been messed about with.

I think its had a fairly big electrical trauma. With the HT disconnected the transformer started smoking, sorted with a good second hand one. I now have all valves lit and 250 dc volts coming out of the transformer.

First problem, a schoolboy error from me, where does the 250v transformer wire go to ? ( I have built a limiter so will use that also).

problem 2, the output transformer primary is open circuit but on the A23 the secondary seems to power something on the tone control. What are my options, obviously get it rewound but is there any other way? Pyes use the EL33 with a normal transformer so can I reconfigure my Ekco ? (I have found a normal one hence my question).
Finally Is it recommended to change the EL33 since the output transformer is open circuit ?
I am aware that I will be changing most of the caps.
Any help will be appreciated
Thans Martin

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Old 19th Sep 2019, 11:21 am   #2
Nuvistor
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Default Re: Newbie with Ekco A23, advice please

The original transformer had a centre tapped HT secondary winding, centre tap to chassis the two end windings each to an anode of the rectifier.
What type of transformer have you replaced it with?
If you still have the original it is possible that it could be rewound.
The output transformer could also be rewound.
See various posts in the services offered thread.
The radio dates from around 1947.

Just one point about your voltage “250vdc out of the transformer”, hope that was AC.
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Old 19th Sep 2019, 11:48 am   #3
HamishBoxer
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Default Re: Newbie with Ekco A23, advice please

Welcome to the forum.Ed Dinning on the group can do rewinds.

The EL33 is possibly just fine.
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Old 19th Sep 2019, 2:27 pm   #4
cathoderay57
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Default Re: Newbie with Ekco A23, advice please

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
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Old 19th Sep 2019, 7:39 pm   #5
Ed_Dinning
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Default Re: Newbie with Ekco A23, advice please

Hi Martin, you have a PM

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Old 20th Sep 2019, 4:22 pm   #6
cornish ekco
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Default Re: Newbie with Ekco A23, advice please

Thanks all for your replies very helpful.
Regards Martin
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Old 20th Sep 2019, 4:50 pm   #7
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Default Re: Newbie with Ekco A23, advice please

Quote:
Originally Posted by cornish ekco View Post
I am aware that I will be changing most of the caps.
In particular C34, which was likely responsible for both your problems.
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Old 22nd Sep 2019, 5:07 pm   #8
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Default Re: Newbie with Ekco A23, advice please

this model was one of my first restorations, Dad had bought it and it lurked in the garage for years until i was old enough to be allowed to touch it.
Great performers these 40's radios, all that bakelite to polish will keep you busy!
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Old 23rd Sep 2019, 2:12 am   #9
MurphyNut
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Default Re: Newbie with Ekco A23, advice please

Ever since I first saw a A23 I wanted one, and I now have one in my collection, they are great sounding and imposing looking sets.
Be careful with the Bakelite cabinet, they tend to be more fragile than they look, the moulding isn't particularly thick.
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