EKCO AC25 mains supply

[crackle]

I was not really sure where this should be posted but it is a power supply for a radio so lets try here.
This came with a KB 429 radio obtained from RWB, it is rather scruffy on the outside, and the transformer has shorted turns.

The multi block capacitor though seems to be fine with very little leakage and each section holds a charge, for a little while. The three sections appear to be 4uF 2uF and 1uF.

There are 2 wire wound resistors with taps for various voltages.

The selenium rectifier also seems to be OK. But as I mentioned the transformer gives a good glow on a lamp limiter and started bubbling away after a short while.
I plan to replace the transformer with one from an old radio and the rectifier with a silicon diode.

I am interested in the original finish to the metal case, it appears to simulate a coppery finish with what looks like blueing.

How would this have been achieved in the old days, and how could it be reapplied after the rust has been cleaned off.
thanks
Mike

[Radio Tech]

Hi Mike

May be the paint finish was achieved by a special paint mix and then baked on with heat treatment.

Ken

[crackle]

I am not sure it is a paint, if it is its very thin.

Mike

[Nicklyons2]

Could it be like the 'blueing' the gun enthusiasts use on their weapons? I'm told by a chap who owns several they soak the metal bits in a (not very environmentally friendly) solution for several hours to achieve the finish; I suppose some sort of anodising.

[mark_in_manc]

I've not done this for a decorative finish, but if you get steel hot (you'll need to read up how hot) and then quench in oil you'll get a 'blued' finish. I'd experiment with some scrap to start with, and be prepared for the oil to catch fire!

[Phil G4SPZ]

Mike, shame about the transformer as your unit looks in good condition otherwise.

I recently restored an Ekco AC18 and wrote about it in Success Stories, top of Page 2 (sorry, can't get my iPhone to copy and paste a hyperlink ). I still don't know how they achieved the external finish.

[Boater Sam]

Is this finish printed on? Hornby train carriages were screen printed, it looks like extreamly thin paint with an almost see through quality.

[Ed_Dinning]

Hi Mike I have 2 or3 of these and they all seem to have a coppery finish that I thought was plating. The rectifiers are normally copper oxide and are usually pretty reliable. I have rewound one or two of this type of transformer.

Ed

[crackle]

I suppose copper plating would give it a base colour, then I wonder if black paint could be lightly sprayed over and when dry, carefully rubbed with a polishing compound to give the different shades of copper and black.

Or maybe I could just paint it with black "crackle" paint.


Mike

[crackle]

I have just finished tracing out the circuit of the EKCO AC25 mains unit.

I find the marking "L" on the mains voltage selector confusing, I wonder what L stands for.

Mike

[Phil G4SPZ]

Mike, I traced out my AC18 and also found the handbook. The "L" is a higher tapping on the mains transformer primary that drops all the output voltages if a lower output is needed.

[Boater Sam]

Its a reverse winding to clip about 20 volts off the primary I think. I've seen this somewhere else but the use of "L" is confusing, Is there not another tapping on the primary other than what you have shown, like 240v? Or is this a 100v to 130v primary only?

[crackle]

Hi Phil
Thanks for the circuit.
Oh b--ger, I think I may have fried the transformer myself, my one is only marked for 112 to 150v I assumed the other tap was the 240v tap. It looks like the transformer was for 110v only.

The strange thing with this AC25 was that the 3 capacitors in the pitch filled metal box all test out OK with very little leakage and seem to hold a charge.

[Phil G4SPZ]

You may not have fried the mains TX Mike, only stressed it somewhat. Try feeding it with 110 volts and see what happens, or a 15 watt bulb in the lamp limiter.

As a 110 volt mains unit it's not that useful here. Maybe it was intended to go in series with a 110 volt LT eliminator? I still can't understand why Ekco would make an HT-only eliminator, leaving the chore and cost of accumulator charging still necessary.

I will try to dig out the literature and post it here, but it may already be on RM.org.

[David G4EBT]

As to the coating, it was most likely 'electrophoretic lacquer'. It can be applied in a range of colours. The object to be coated is a cathode rather than an anode (as in anodising, used for aluminium, which can be done on a DIY basis. 'Electrophoretic lacquer' is commonly used to plate cheap steel hardware to make it look like brass or copper.

There's a bit about the process here:

http://www.midlandpolishing.co.uk/el...retic-lacquer/

Don't know how much it costs. Though it's a form of electro plating, modern electrophoretic lacquer is electro-deposited from a solution of specially formulated polymer resin dissolved in water. Could well be a cheaper process than say as nickel or chrome plating (not that such options are relevant to this thread). It's only 8 microns thick and isn't as durable as metal plating such as chrome, so can't be used for outdoor applications.

Personally, for a cheap option, I'd be inclined to spray the case with acid etch primer for steel, (see e-bay), then metallic bronze, to be as close to the original finish as possible. (Ordinary grey primer gives poor adhesion).

Hope that's useful.

[Phil G4SPZ]

Found the Ekco leaflet: http://70.33.246.110/~radio100/allan...%20booklet.pdf

There is a specific model for 100-125V mains, yours must be one of them. Quite rare I think. Clearly a new TX would be the way to go. The secondary could be about 110 volt AC to give around 150 volts DC once rectified and filtered.

[Ed_Dinning]

Hi Gents, pri could be reconfigured for 240v as part of a rewind

Ed

[crackle]

Hi Phil
Thanks for finding the leaflet, I have saved a copy for reference.
One thing is certain, as this unit was still connected to the KB 429 radio in which it came in with its 2 pin 5 amp plug, it proves the radio has not been used for a very long time. How long is it since there was 110v supplies in the UK?

My plan is to replace the transformer and copper rectifier with 2 transformers. One will supply a low voltage, possibly 9 + 9 volts and one winding will supply a regulator for the heater supply. The other 9v winding will supply the low voltage winding of another mains transformer, possibly again a 9 + 9 v to 230v one, to step up the voltage to supply approximately 150 volts to the original Ekco circuitry.

Mike

[crackle]

Going back to my original query about the, what must have been at one time, attractive black and copper finish to the outer case. The black is not a paint, acetone has no effect on it, and the copper was plated on first, as after some vigorous rubbing with polish the black wore away to revel copper.
So I don't know if that confirms the 'electrophoretic lacquer' process that David mentioned above. If it was a polymer coating I would have expected it to respond to aggressive solvents like acetone and cellulose thinners.

Mike

[boxdoctor]

I wonder if the black finish is actually 'real' (baked on) vitreous black enamel?
It would resist most of the common solvents, I suspect. Tony