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Old 18th Jul 2017, 8:51 am   #21
crackle
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Default Re: Restore of KB 428

I see what you mean, but it would be a lot smaller than the original.
Would be nice to get something like the original.
Mike
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Old 18th Jul 2017, 9:48 pm   #22
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Default Re: Restore of KB 428

Today I borrowed the power supply and speaker from my KB 540. The power supply is luckily electrically identical to this KB 428.
I made a start on the wooden base for the shelf of the new power supply and went to see the local blacksmith about a piece of steel for the PSU chassis. The size of the steel plate needs to be 28.5cm x 11 cm deep with a 2.5 cm fold made at the front.
I should be collecting it tomorrow, Wednesday.

My order of capacitors arrived and I fitted the final new capacitors today.
When I connected up the PSU and speaker, the first test was with the lamp limiter. This went OK, I could hear hiss and crackles in the speaker and the lamp gradually died to a dull glow as the heaters warmed and the current stabilised. The voltage was still to low for the RF valves. I switched out the lamp limiter and started to receive radio signals, mostly interference which has become very bad here lately.
When tuned to a station the audio was VERY distorted, I checked things over and substituted valves from the 540, but no improvement.
Voltage checks on the valves showed that V3 cathode had over 26 volts. This was caused by the cathode resistor R9, 600 ohms, being open circuit, one I must have missed. I searched for ages and eventually found a suitable resistor.

Now the radio was really working, lots of stations on MW and even more interference, and a a surprising number of stations on LW.
I have taken a short video of the radio working.
I love these old superhet radios.
It does not seem to need any realignment, all I have done is align the dial station name disc. How's that for over 80 years old.

https://youtu.be/WEHzuYQcF8U

Mike
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Old 20th Jul 2017, 6:48 am   #23
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Default Re: Restore of KB 428

I have made a provisional layout drawing of the PSU chassis. I transferred it from the laser printed image on paper onto the metal work using the tried and tested method first shown to to thousands of Blue Peter viewers by, I think, Valerie Singleton, when she made some DIY T shirt designs.
If you did not see this, then the method I used was; make the drawing life size scale, create a mirror image and print onto paper with a laser printer.
Attach the paper to the metal work, wipe over with a tissue moistened with white spirit, then use a hot iron to "iron on" the laser toner to the metal work.

The layout showing the cut outs needed is not really final yet as I still have to gather together the parts like the mains transformer, but small adjustments can be made or it can be stencilled on again using the same method if the parts I finally use are much different.

Mike
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Old 20th Jul 2017, 9:33 pm   #24
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Default Re: Restore of KB 428

Well I guess a new power supply shelf wouldn't look the same without some sort of condenser block, so I a made a false one, purely for cosmetic reasons, the actual electrolytics will be hidden under the shelf.

Mike
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Old 20th Jul 2017, 9:36 pm   #25
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Default Re: Restore of KB 428

Very good. It looks suitably waxy.
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Old 21st Jul 2017, 4:15 pm   #26
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Default Re: Restore of KB 428

I have photographed another identical dial with a 24M pixel camera and cleaned up the image.
It should also be suitable for the KB 540 & 550 and also probably KB 426, 429,
Here it is;
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and here is in a PDF form which should print at the correct size, which I measured at 149mm diameter.
428 dial.pdf

Mike
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Old 25th Jul 2017, 8:30 am   #27
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Default Re: Restore of KB 428

If you happen to come across one of these radios then check that there is a link in the lower 2 "Gram" sockets.
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This is needed to connect the radio volume control to chassis, with out it the volume control is ineffective, being at full volume all the time, which was a bit alarming.
In my case I made a link from some 3mm galvanised wire and bent it into a U shaped loop with 1/2 inch between the centres of the prongs.
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The radio is now finished, the cabinet has had some of the scratches touched up and it has had a good polish with wax.

I have used the PSU and speaker from my KB 540 for this radio and the new PSU I will be making will go into the 540. The reason for this is; the 540 cabinet was already severely damaged when I got it and I did some extensive work to make it presentable.
So although it looks better and appears almost like it should it is far from original so a non original PSU doesn't seem to matter to me. Whereas this 428 cabinet is almost original and it seems nice to have a more original PSU.
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Old 25th Jul 2017, 9:26 pm   #28
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Default Re: Restore of KB 428

I have taken some photos this evening, they come out better at night when there is less light bleeding through the curtains.
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I have also made another video and uploaded it onto the Radio Museums Youtube channel.


Mike
p.s.
The Radio Museum only wish to link to videos on their own Youtube channel.
So if anybody would like to add a short video, linked to the actual model page in the Radio Museum, demonstrating their radio working, please contact me.
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Old 26th Jul 2017, 7:45 am   #29
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Default Re: Restore of KB 428

Hi Mike that looks very nice ,I have a radio using the same cabinet but I don't think it's a KB ! .Let us see the new p/s when you have finished it . Mick.
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Old 26th Jul 2017, 7:54 am   #30
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Default Re: Restore of KB 428

Thanks,
I would be interested in seeing your radio.

Mike
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