Restoration of a KB 428

[Crackle]

I have not done many restorations lately, but decided to start on one I have been meaning to do for some time. I bought this fine 1935, KB 428 radio some time ago. It features a neon tuning indicator and "Fototune" dial, which shows one station name at a time through a window.
However it is missing its speaker and power supply shelf.
   
   
more details can be seen here http://www.radiomuseum.org/r/kolsterbr_k...b_428.html

I also bought this old Alba 815, with the view to using the mains transformer to supply the HT and rectifier heater and OP valve heater. You can see the actual one here in the radio museum, http://www.radiomuseum.org/r/balcombe_815.html .
However I think I failed to realise at the time that the rest of the valves in the KB 428 were 13v heaters. So it looks like I will have to include an additional approximately 12v transformer to run the 13v heater supply.

I will need to make the complete PSU shelf for the transformer, rectifier, capacitor block and speaker transformer, and associated components.
   
I will also need to find a 9 pin plug to fit into the socket on the main chassis.

Thinking about it though, it does seem a shame to use the Alba as a donor set as the cabinet is in very good condition. I dont suppose there is anyone who would like to swap the Alba for a suitable mains transformer, energised speaker and OP transformer?


Mike

[Crackle]

I have removed all the valves, being careful to lever off the top cap clips by prising a thin screwdriver under the clip and between the cap to save stress on the cap and wire in case the cap came loose.
All the 13 volt valves, 9D2, 15D1, 9D2, 2D13C, heaters test good, at around 11 ohms, and the OP valve, a KT41 in this case also tests as heater good. The tuning indicator is a Cossor 3184 and this looks a bit dark on the inside of the glass, but hopefully will still work.

The bad bit found so far (apart from the missing PSU and speaker) is the tuning dial film disc has been rubbing on the metal dial backing and scored a line all the way round it. It is still readable with a bit of imagination but will detract a bit from its looks when working.

It looks like someone has been in the underside of the radio at some point in the past.

Mike

[Crackle]

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

[peter scott]

Interesting to see a "tuneon" in operation and also the novel station name arrangement.

Peter

[TNC]

Well done Mike - that sounds quite excellent...and a very enjoyable Youtube video. The tuning indicator is most impressive.
atb. Trevor

[Crackle]

Hi
Thanks, I was impressed with the tuning indicator as well, but it does need a good high HT to make it reliable. I tried 3 rectifiers, eventually I found one which gave an HT (measured at OP valve anode) of nearly 230v. The original rectifier from the KB 540, which only gave just over 205v, will go back into the 540 as that radio has no tuning indicator and one less valve.
There is a trimmer potentiometer for adjustment of the tuning indicator, manual says 1/4 inch long when no signal. But I have found it is better if it is set to about 1/2 inch, it seems to give a larger range of length.

Mike

[Crackle]

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;
   
 
I have also uploaded it to the archive in PDF form which should print at the correct size.
http://golbornevintageradio.co.uk/forum/...p?tid=6456

Mike

[Crackle]

This restoration is now complete. 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.

The "Tuneon" neon tuning indicator works really well.
               

Mike