KB 3 valve Masterpiece

[crackle]

At long last I have obtained one of these radios for the KB museum, it looks to be in more or less original condition. (there is a MES bulb and holder in series with the HT- and GB+, I dont think this would be original)
You don't get to see many of these so I thought I would share it with you.


The radio was manufactured by KB for Godfrey Davis for a second attempt at running a campaign where one could exchange BDV Cigarette Coupons for the radio.

You may recall that the original and well publicised BDV campaign was for a small Bakelite "Masterpiece" about 8 inches cube. see http://www.radiomuseum.org/r/kolsterbr_masterpiece.html

This Masterpiece radio is a more substantial model with 3 valves in a nice solid oak cabinet with decorative veneers on the front ply panel, and an interesting and unique speaker fret.
It is battery powered, with HT voltages of 100v & 70v and with LT of 2v.
It includes a Screen Grid valve for the RF amplifier and triode valves for the detector and output valves. My example is fitted with a Cossor 215SG, Mullard PM1HL and Mullard PM2A.

In interesting feature of the radio is the tuning capacitor drive.
It has a ganged tuning capacitor with additional fine control. Both capacitors moving vanes are controlled together, by the outer knob, but by turning the centre knob the rear capacitor "body" can the rotated 20 degrees independently of the front capacitor. It will be interesting to see how effective this is when I test the radio.


Tests so far show the magnetic reed speaker to have a healthy 2.3k resistance, but the inter valve transformer has one half of the secondary open circuit, so I will bridge across this when it comes to testing. The 3 valves all have good filaments.

It would be interesting to hear from anybody who has one of these sets, so that we may ascertain how many there are.
I would also like to hear from anybody if they have seen these types of resistors used in any radio sets prior to 1932.

This style of resistor does not seem to be used in any other KB radio until 1933.
I believe the date of this model may be later than originally thought. It is my belief that it dates from around 1932-1933 and not 1931 as mentioned in Radio Radio.
Another factor making me feel the date may be later is that KB issued a notice in December 1930 agreeing to not accept any more coupons for exchange for radios. see http://www.radiomuseum.org/forumdata...se_coupons.png
I wonder if this was simply to placate the KB authorised dealers, and maybe a reason why there are no markings on the radio to associate it with KB.
It does seem strange to start a new agreement with Godfrey Davis so soon after KB had agreed to finished the first campaign.

Mike

[Radio Tech]

Hi Mike

The resistors do look as if they are original and that is a very nice looking set for its age, it would be great to know if the set still works once a power pack has been made for it.

Ken

[HamishBoxer]

Great find Mike and I wonder where it came from?

Not forgotten to get those other photos done of the 283.

[John M0GLN]

Lovely set, old KB's are probably my favourites, I've got a Kobra and Brandeset in my collection plus a more modern Toaster.

John

[crackle]

The radio works, as is, all that has been done is bridge the faulty section of the intervalve transformer.
My tests were carried out using the workshop speaker via a speaker transformer.
I cant say the performance of the radio is particularly good. The dual capacitor with separate control over the rear one does work, I would need to draw the circuit to know exactly what it is doing. With careful use of the reaction control stations can be heard across the MW and even R4 on LW. (this was not evident on the video)

I have put it back together and tested with the original magnetic reed speaker and as, I think, Gerry said, it sounds like a wasp in a bottle. The speaker is simple and is one step up from having no speaker, at least the whole family could listen to the radio at the same time.
Here is a video of the set working with the workshop speaker. https://youtu.be/qp0wuwDKcvE


Mike

[crackle]

Originally Posted by Radio Tech

The resistors do look as if they are original and that is a very nice looking set for its age, it would be great to know if the set still works once a power pack has been made for it.

Because I have not seen KB use this type of resistor in any radio prior to 1933, (they were common from 1933 to about 1935) I am basing my argument that the radio was later than 1931 on the type of resistors used.
The normal type of resistor which KB used in 1931 was like this.


Can any one please confirm if they have seen this style of resistor, seen below, used in any other make of radio prior to 1932.


Thanks
Mike

[crackle]

Here you can see the official video made for the Radio Museum.
This time the radio is working with its original magnetic reed loudspeaker. The speaker needed a minor repair to replace the rubber washer on the adjustment control.
https://youtu.be/cVhda0A67zU
Mike