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
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
