EKCO

VINTAGE RADIO WORLD - EKCO

ekco

restoring a U76 'consort'

Here's a guide to a typical restoration of a valve radio chassis. The example set is an

EKCO U76 'CONSORT'

It is effectively in two sections: first, pictures taken during the restoration, with brief comments. Second, a text description of some of the problems faced and how they were overcome.

WARNING: lots of high - definition pictures, this page may take time to load.

(I think it's worth the wait)

	This set was bought at auction. It uses an AC/DC 5 valve (inc. rectifier) chassis with medium and long wave coverage. The cabinet is a bakelite moulding in the typical 'Walnut' effect, but with an inset grille of cream self-coloured plastic. The glossy quality of this leads me to think that it is an Acrylic casting. Left: as purchased
	The cabinet has some rather odd design points. As the pictures show, it is an unusual shape. This makes for an interesting chassis design, where a shallow bottom section of metalwork supports the power supply components, with a vertical chassis section carrying the rest. This means that the amplifying valves are in a horizontal position, something that can lead to electrode 'sag' with certain valves, although this is unlikely with the range of valves used here, as it tended to affect the later frame-grid TV types which had extremely closely spaced electrodes.
Above left: the chassis from the rear, showing the heavy cardboard 'baffle board' carrying the loudspeaker

Above, left: the cabinet stripped of the works. Right: Another view of the chassis, showing an orderly though unusual layout
There is no dial lamp as such, the single bulb being used to illuminate a small circular beacon mounted centrally below the dial, on the front of the cabinet. The controls are unusually placed, being diametrically opposite each other in recesses in the sides of the cabinet. The 'knobs' are two large Bakelite discs which have a finger indentation for adjustment. Right: the components of the cabinet after initial degrease and clean, awaiting polishing. The 'white' panel at the bottom of the picture is actually the cream-coloured grille. It doesn't show too well!
The chassis was, happily, not too corroded and the layers of dirt cleaned away readily with the application of foam cleanser, using a combination of toothbrush and paste brush. (I have a separate brush for my teeth, by the way)

Above: thorough vacuuming and surface cleaning complete, the chassis is now ready for electronic restoration work to begin
	I feel that nothing looks more unprofessional that messily re-soldered tags on components, so the volume control was removed for cleaning and rewiring. Parts of the main ballast resistor wiring was changed at the same time, as was the wiring to the indicator lamp - and the lamp itself, expired due to a failure of its shunt resistor

Above: with the baffle removed, access to the component side of the chassis is easy
	Here's a selection of the coupling and decoupling capacitors taken from the set. These waxed paper types were extensively used in most UK radio production, for AF coupling and decoupling, AGC and HT decoupling and various tone correction purposes. They are always high on my list of suspects.
This shows the dial drive arrangement. The flax cord is taken around pulleys from the drum assembly - a fairly basic and easy arrangement to re-string. Nylon fishing line will suffice for this task but if you can obtain the 'right' material, the authenticity of the restoration can be maintained. Besides, flax has more 'tooth' than plain nylon line, and grips the control spindle better - in my opinion.

General comments

Viewed from the front, the left-hand knob is the on-off/volume combination, whilst the right hand knob is for tuning. Wave-change is by means of a further, smaller lever-shaped knob on the right side.

All in all, it really is a 'love it or hate it' design. I must admit that it grew on me, the more I worked on it. I do like the layout, which has a logicality, once you accept the cabinet design, and the set is, as usual with Ekco, strongly constructed with a feeling of durability.

Valve line-up is Mullard: UCH42 (frequency-changer/local oscillator), UAF41 or 42 (I.F. amplifier/agc det, vari-mu), UAF41 or 42 used again (this time as det/AF amp) and UL41 (AF output). Power is provided by UY41 (rectifier)

First things first...

The mains lead was in urgent need of replacement - it had been cut off. I bored out the hole in the chassis through which the lead passed and fitted a grommet, to protect the new lead. The old lead clamp was brought into use to tether the lead with a little slack behind the outlet.

Initial checks

Powered up using a test lamp, it was obvious that the indicator bulb was o/c. Replacing this gave a quite brilliant light and it was obvious that, off the test lamp, the bulb would have a short if spectacular lifespan, measured in milliseconds. A glance at the circuit showed a possible culprit - R21, a 33 ohm pilot lamp parallel shunt. Cold checks with meter showed this to be very high resistance, overloading the lamp. I fitted a 47 ohm 2 watt resistor and this worked well with a 6V torch bulb. 33 ohms would have been fine, but the bulb seemed to be rather dim with that value. Possibly the original bulb was rated at a different current to the one I fitted - the data wasn't clear about that point and the old bulb was completely corroded and unreadable.

Next problem was odd. The bulb would come on, then go off again, cycling through this on-off state with a remarkable degree of regularity and never staying on long enough for the valves to warm to operating temperature. It was clear that there was an intermittent supply fault of some kind, but what? Again, the circuit diagram was consulted. The dropper resistor taps were monitored 'hot' but these only rose to full AC potential whenever the lamp went out. It wasn't the dropper, then, or the voltage would have disappeared. This left only the valves and as I'd had much trouble in the past with UL41s, I changed the output valve and solved the problem. Intermittent heater.

Next, A quick cold check on the resistance of the smoothing and reservoir combination capacitor, which in the event read comfortably high and swung the ohmmeter needle in a way that suggested a fair amount of capacitance remained.

First full power test

Under full power, the set gave a good account of itself, working on it's frame aerial. Various points were noticed - some rather excessive sound distortion, crackling from the wave-change switch, crumbling insulation on HT and aerial wiring. Time to get to work. After a general chassis clean, as shown above, the dial drive components were disassembled, cleaned, reassembled and re-strung. I Removed the heavy cardboard baffle that carried the loudspeaker to gain access to the components. I replaced the following capacitors: C18 (AGC decoupling), C21 (V2 cathode by-pass), C31 (tone correction), C25 (AF coupling), C2 (earth isolator, C7 (HT decoupling) C10 (V1 cathode by-pass)

I also replaced the surge limiter R22. This large carbon stick component looked very much the worse for wear, though it read fairly accurately. Changed for sake of completeness - besides, I don't like the look of burnt components.

Finishing touches

After partial rewiring to power circuits and frame aerial connections - the latter butchered by someone at an earlier time), switch, valve-holders and volume control cleaning, the set was reassembled and tested. Though still only on the internal frame aerial, impressively good results on medium and long waves were obtained. Short waves less so, but after dark, found to work very well. A short aerial wire improved SW response, which was to be expected.

Of course, all cabinet parts were fully restored but as this section is about the chassis, the cabinet is another story...

An unusual set, but now immaculate.

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'RESTORING VALVE RADIOS'

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