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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 9th Dec 2020, 12:58 pm   #1
kalee20
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Default Illuminating an Ever Ready Sky Monarch

The Sky Monarch was Ever-Ready's flagship, battery, sideboard radio. It has most of the features of the more posh of the mains sets - switched gram input; tuning indicator; large-diameter loudspeaker; polished wooden cabinet. And the push-pull DL96's have it sounding almost as powerful. But the one thing which leaves it rather soulless is, the scale doesn't light up.

Members of the BVWS may have noticed my Bulletin article about lighting the scale of a Vidor attaché case portable. I didn't stop there; I went on to light-up an Ever Ready Model K, and then... having picked up a Sky Monarch AM as a present for a good friend (who has similar views on unlit scales), and bringing it to working order, I wondered...? Especially as there's also my own, AM/FM version, so having got the design right I could do a (very limited!) production run?

It obviously wasn't designed with scale illumination in mind. I set myself a challenge, if I could do it without drilling the chassis, or carving into the cabinet, then I would.

There is precious little room available, however there is clearance below the pointer. And the pointer guide rail has a couple of emerging bolt-ends which might just secure a LED mount. Cutting a strip of 0.8mm SRBF, trying it for space - yes, possibly. The control shafts get in the way, but by positioning six LEDs between the shafts, there actually is room. By the third mock-up, I had something workable.

The scale itself is moulded Perspex (or similar). It's fixed to the cabinet, not the chassis. The LED position is below the concealed edge of the plastic, so light gets launched into the thickness of the material which is very effective. Experimenting with LED colour, warm white is most suitable.

One problem is that the bolt-ends were just not quite long enough. Changing one screw for a longer one is dead easy. The other... well, the head is covered by the wavechange switch; the wavechange switch is not only fixed to the chassis by its bush, but along its length between the wafers as well... though it actually sits on a sub-chassis mounted on shock-absorbing grommets. After removing the speaker baffle, stripping the drive cord, and other discombobulation, screw replacement was possible. I took the opportunity to replace the rather crude bushes that the pulleys run on, with a better design, courtesy of a local machine shop who made them out of brass for me. The two ends of the pointer rail are mounted differently: one is on the main chassis, but the other is on a short extension plate bolted behind the chassis, so the new screws need to be slightly different lengths owing to the 1.25mm thickness of the chassis steel. It's that space-critical!

The LED strip itself, needing holes and cut-outs - one, I'd be happy to make. Two - twice as much time, so I looked into laser-cutting prices for 0.7mm sheet brass. Quote for 3 (one spare) would set me back less than £50 inclusive of material. Saving at least 2 hours work alone, that's a no-brainer, thank you Falcon Precision! Off went a .dxf file and order.

The 3mm diffused warm-white LED's, 6-off, are connected in parallel. I did select from a quantity of 20, two sets of 6 matched for forward voltage at 2mA, but to be honest there is little difference between them, and the parallel running works well. I made clips out of 0.25mm brass, soldering them in position using a positioning jig made from an MDF offcut. The LED's themselves are held in place with holt-melt glue, which covers and insulates the twin power busbars, and anchors the leadout tails.

The Sky Monarch takes (according to Trader sheet) 13.95mA and it has a back-bias resistor of 470Ω. Replacing this resistor with the LED's and 270Ω in series gives the same bias voltage, so we're using profitably some of that wasted voltage drop. I put a 10V, 1.3W Zener diode across the whole thing - it doesn't affect normal operation as bias voltage is about 6.5V, but it does divert the switch-on surge away from the LED's, as the battery charges the HT electrolytics. And, there's 47Ω in the HT+ lead, to minimise the surge to under 1.7A.

Reassembling... well, you can see the effect, the Sky Monarch now looks like a proper grown-up radio!
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Old 9th Dec 2020, 7:31 pm   #2
Ed_Dinning
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Default Re: Illuminating an Ever Ready Sky Monarch

Hi Peter, it looks good. Have seen your previous article I'm now tempted to try it on my Sky Emperor (which is fitted with a mains PSU)

Ed
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Old 10th Dec 2020, 1:25 pm   #3
kalee20
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Default Re: Illuminating an Ever Ready Sky Monarch

Hi Ed,

Would be good to hear how it goes!

I have not played around with a Sky Emperor, though I get the idea that they are slightly more plentiful than Sky Monarchs. Though having looked at the circuit diagram, the copious switched bias resistors for AM, FM, Normal and Economy mode is a challenge in itself!
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