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

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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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Last edited by crackle; 18th Jul 2017 at 9:58 pm.
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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 Yesterday, 4:15 pm   #26
crackle
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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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