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KB 540 1936 Superhet Receiver

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Anonymous
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The next project is this radio, which I will just try and politely describe as "beyond scruffy".
I bought it off Ebay for £10 and have had it lurking in the garage for just over a year now.

The best bits;
There are not that many woodworm holes, the mains and speaker transformers test OK, the speaker field winding seems OK at just over 1K ohms, and I should have a spare 4 volt rectifier to replace the missing one with a bit of luck.
The HT winding is giving a healthy (if not lethal) 295v, there is also a 12.6v winding, a 4v winding for the rectifier and another 4v winding, not quite sure yet what this is for as the 12.6v winding looks like the main heater supply by the thickness of the wires..
I will have to build up one corner of the dial escutcheon.
The basic parts of the set all seem to be present so it should be able to be made a goer.
But I dont think I will bother trying to reform the main smoothing capacitors. :aak

 
Posted : 09/06/2015 1:17 pm
Anonymous
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I forgot to say, the original speaker grill has been replaced with a brass gauze. When I removed the speaker and baffle from the cabinet there was a remnant of the original cloth still stuck to the baffle, it was typical pale loose cloth weave that KB used in the late 30's. At least I know what it would have been like even if there is no equivalent available now days.

The valve line up is 15D1 9D2 10D1 7A3 R2 the first 3 valves are 13 volt heaters and V4 & 5 are 4 volt heaters.
I hope V1, 2 & 3 work OK as they don't sound like they are very common.

Here is the circuit diagram.
Mike

 
Posted : 09/06/2015 5:04 pm
mark pirate
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KB had a thing about fitting 13v valves, my 510 uses an odd mixture of Mullard & Brimar valves.
There are equivalents for the 9D2 (VP13C, C50N, 12VPA), I used a VP13C in my set.

My set was also a bit of a wreck, but turned out quite well : http://www.vintage-radio.net/forum/show ... hp?t=76098

 
Posted : 09/06/2015 8:12 pm
Anonymous
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Hi
Has anybody got a photo of a KB 540 that I could see, just so that I can get a better idea of how it should look.

Thanks
Mike

 
Posted : 10/06/2015 1:15 pm
Herald1360
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Not too sure about the live mains present on the 9 pin plug if the PSU is plugged in to ac and unplugged from the radio :ccf

.........._______
.....___/|__|__|____
.=.( _---__|___|_---_)
.........O...Chris....O

 
Posted : 10/06/2015 10:56 pm
Cobaltblue
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Hi Mike

What a cracking set its such a pity its in such poor condition.

As a great fan of 1930's sets I can quite see why you would want to restore it.

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 10/06/2015 11:03 pm
Boater Sam
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Will make a nice set when you have done.
If you need any valves, let me know and I will see what I can find. I have an MU14 which is a super version of Mu12 which is equivalent to R2.
There seem to be lots of equivalents to most of the valves listed in your set.

Sam.

Boater Sam

 
Posted : 10/06/2015 11:42 pm
Anonymous
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This is the only image I have to go on for its trim and finish.
The parts I need to know more about are the to dark bands above and below the speaker grill, arrowed.

Are these just a dark veneered wood, say ebony or something, or just painted dark. Do they come out flush with the vertical parts either side of the grill, or are they recessed. I suspect they may be flush.

Mike

 
Posted : 11/06/2015 4:39 pm
kalee99
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Hi,

I had one of these sets many years ago. The bars top & bottom of speaker grill were painted black on mine as the black had flaked off in places, but I cannot remember if they were recessed from the rest of the facia.

Paul.

Do not let the Blue smoke escape!

 
Posted : 11/06/2015 6:25 pm
Anonymous
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hi Paul
That helps a little. I have to fabricate the 2 parts to go above and below the speaker as they have been cut away. If they were painted that helps having to find decorative wood for them.

Thanks
Mike

 
Posted : 11/06/2015 8:18 pm
Anonymous
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The day before yesterday I started repairs to the cabinet, a bottom side corner had come apart at the tongue and groove glue joint, the other had split the wood forming the corner at the top left corner. The front panel was unattached on 3 sides.
First I glued the sides together again.

Then the front panel was glued and clamped over night.

The tone control on this radio consists of altering the IF bandwidth and switching in a capacitor.
One switch contact for the tone capacitor had broken off and was nowhere to be found. This morning early I busied myself repairing and making a new contact for the tone control switch. I replaced the original broken paxolin with a piece of scrap veroboard, and used a brass screw and nut with the screw head flattened for the stationary contact.

I also took a closer look at the construction of the wax paper capacitors. I was intrigued as to what the stranded wire was that was attached to each end of the capacitor wire.

Rather than attaching a foil to the inside of the end caps, they have brought the connection to the foil outside the end cap and then spot welded the wire to the capacitor lead.

Back to the shed now to make the 2 wood trim pieces which go above and below the speaker grill.
Last night I scaled the B&W image of the radio in a drawing package and measured the height of the wood trim, about 32mm for top and bottom will hopefully keep the ratios of the trim to the rest of the radio consistent with what it probably was when original.
Mike

 
Posted : 12/06/2015 10:48 am
Anonymous
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Ian B (on UKVRR) has sent me some photos of his KB 550 which would appear to be the AC/DC version with the same cabinet.

So I have something to model my repairs on now.

Thanks Ian

Mike

 
Posted : 17/06/2015 4:06 pm
Refugee
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That looks like a wooden profile that could be bought from a picture framers.

 
Posted : 17/06/2015 5:29 pm
Anonymous
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Yes possible but I should have some suitable wood and be able to machine it myself. I am just waiting on some dimensions to be confirmed from Ian.
It seems it was a very dark and dull looking radio cabinet.

Mike

 
Posted : 17/06/2015 10:10 pm
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Over the last few days I have been repairing the broken Bakelite dial escutcheon.
I decided against using glass mat as it is too messy and the work was too small and detail fine. So I cut a right angled shape out of some very thin steel sheet, the sort of sheet steel that may be used as a screening can. Then I cut a compound curve, bending and matching it to one of the other corners.
I ground back the Bakelite near the edge of the broken edges enough to take the thickness of the steel and a little epoxy, one piece broke off during this process as there was a further crack, but I used superglue to fix that back into position.
After gluing in the 2 steel shapes I covered the epoxy with polythene, and I left it to harden over night.
I waxed a brass screw and fitted a nut on the end then built up epoxy around the screw. I have run out of epoxy thickener so the glue would not mould well and stay in a high lump around the screw and nut. But after a couple of hours the epoxy had stiffened to the consistency of putty and I was able to fashion it more into the correct shape to fit into the recess in the cabinet.
I think the following photos should explain the rest of how I did it, other than to mention it took about 4 or 5 attempts of filling and filing to finally get the correct profiles.
I am happy with the result and it sits nice and flush on the dial opening.

Mike

 
Posted : 17/06/2015 10:46 pm
Anonymous
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Wonderful work on bezel!

13V valves may have been also used in car Radios. Though most cars then were 6V. Certainly vibrator packs used in 1930s.
Earlier car radios simply used the 6V for direct filament and a disposable HT. Earlier still the radio had its own 2V, 4V or 6V lead acid as the car might have not have had one (magneto, crank etc, even my 1960s vespa had no battery, so when stopped the the head lamp was orange and flickery). I don't know when cars stopped using acetylene lamps and used 6V or 12V headlamps.

 
Posted : 17/06/2015 11:09 pm
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Looking at the chassis of Ian B's KB 550, there appears to be no can fitted where L1 is mounted on the 540 (to the left between the dropper resistor and the rectifier valve).

Mike

 
Posted : 18/06/2015 10:16 am
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I have finished the restoration of the electronics, all wax paper capacitors were replaced, and about 3 resistors which were way out. The paper capacitors were all marked as made by STC, and where possible I restuffed the capacitors, the method that STC used in their construction made it very easy.

The dial bulb holders were falling apart because the central rivet had corroded away. I cleaned the brass and soldered the central contact to the spring. This held it all together, then I used superglue just to lock all the parts to stop then rotating.
The bulb holders now work fine and will be OK so long as the solder holds out.

I had previously cleaned and rubbed down the front panel of the cabinet and given it a protective coat of thinned varnish.
Today I have been working on the cabinet again, making the two profiled pieced of wood that someone had previously cut away when they fitted the metal speaker gauze.
The 2 pieces of wood trim pieces will be painted black along with the top and sides of the cabinet.

Its starting to come together. Its never going to be perfect, there has been some damage to the decorative veneers, but it will at least, look presentable, at least it should with a bit of luck I think.

Ian B has offered his KB 550 to me (seen above) to add to my collection of KB radios.

Mike

 
Posted : 22/06/2015 12:43 pm
Anonymous
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Well at long last I can now present the KB 540 with a degree of pride.

It has taken about 5 coats of lacquer with a light rub down between with 600 grit, and then a final rub down with 1200 grit for the last coat.

The front decorative veneers were a but patchy and the veneer in the area where the dial and controls are, had it seemed, been laid oddly so that from one angle the left half looked darker and from the other angle the right side looked darker. This area was darkened with a little "toner" in the varnish.

The 2 veneered side panels are were made a little darker from their natural colour, with a little home made toner in the varnish.

The top and sides were stained with my own mixture of diluted varnish, darkened with Jacobean dark oak, rosewood, small amount of black paint and a very small amount of brown paint. It took quite a few coats to get the effect about right. In strong light you can just see the grain of the birch ply through the stained finish.
It was very difficult to get the cracks and pores in the top and side panels to flatten, but at least they show that the cabinet is made of wood.
The knobs seen on the radio are "borrowed" from my KB 426.
It currently has pride of place in the living room.

Mike

 
Posted : 29/06/2015 11:20 am
Cathovisor
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<speechless >

 
Posted : 29/06/2015 11:28 am
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