13-11-2018, 09:04 AM
The other day I was in the KB Museum, tidying up and trying to make some room and I discovered a radio which I had not added to my website.
I had only ever taken one photo and put that on the Radio Museum. I expect I was waiting till I was able to do some work on it to get it working and looking smarter.
Anyway what started off as a quick spruce up ended up with the chassis on the work bench.
It is a fairly simple radio as it is TRF design and lacks a mains PSU, there is only the one 2uF electrolytic on HT2 the supply for the OP valve.
The valves are VP21 HL2 and PT2.
Preliminary tests show the intervalve transformer to have an approximate 600 ohm primary and a 6k ohm secondary (manual gives 5K), the OP transformer has a 900 ohm primary, which seems a little high but tallies with the information in the KB service manual.
The simple open cam operated switches are all in good condition, I have cleaned the contact surface and sprayed with switch cleaner.
The volume control is combined with the reaction control it comprises of a 10k variable resistor with a 280pF variable capacitor mounted on the back of the pot and sharing the same control shaft. I hope this pot is going to be OK I dont fancy dismantling it.
The main 3 gang tuning capacitor was rather stiff and the simple cord driven drive was slipping. I have spent some time attempting to re-align the scale and the waveband indication mechanism to try and minimise friction. The bearings have been cleaned and lubricated as best I can with out dismantling everything and together with moving the drive cord tension spring to the next anchor point the tuning now works with out slipping.
The tuning dial disc appears to be made from a card coated in a white finish and printed with the station names. There is no indication of frequency or wavelength. It is rather scruffy but it probably wont even show much behind the yellowed cellulose window.
There was one very rusted screw fixing the chassis in the cabinet, the other 3 undid easily. The rusted one sheared as I tried to turn it. When the chassis was removed I cut the remaining stub off flush with a Dremel and mini cutting disc and drilled through the centre of the old screw. All the other screws were the same self tapping type but the holes were tapped for 2 BA so I will be replacing them all with 2BA screws.
Next job will be tackling the capacitors, I dont expect to have to replace any resistors as this type used by KB are normally very accurate.
But that will be later as I am off to make use of the sunny weather to cut ply for another shelf.
Mike
I had only ever taken one photo and put that on the Radio Museum. I expect I was waiting till I was able to do some work on it to get it working and looking smarter.
Anyway what started off as a quick spruce up ended up with the chassis on the work bench.
It is a fairly simple radio as it is TRF design and lacks a mains PSU, there is only the one 2uF electrolytic on HT2 the supply for the OP valve.
The valves are VP21 HL2 and PT2.
Preliminary tests show the intervalve transformer to have an approximate 600 ohm primary and a 6k ohm secondary (manual gives 5K), the OP transformer has a 900 ohm primary, which seems a little high but tallies with the information in the KB service manual.
The simple open cam operated switches are all in good condition, I have cleaned the contact surface and sprayed with switch cleaner.
The volume control is combined with the reaction control it comprises of a 10k variable resistor with a 280pF variable capacitor mounted on the back of the pot and sharing the same control shaft. I hope this pot is going to be OK I dont fancy dismantling it.
The main 3 gang tuning capacitor was rather stiff and the simple cord driven drive was slipping. I have spent some time attempting to re-align the scale and the waveband indication mechanism to try and minimise friction. The bearings have been cleaned and lubricated as best I can with out dismantling everything and together with moving the drive cord tension spring to the next anchor point the tuning now works with out slipping.
The tuning dial disc appears to be made from a card coated in a white finish and printed with the station names. There is no indication of frequency or wavelength. It is rather scruffy but it probably wont even show much behind the yellowed cellulose window.
There was one very rusted screw fixing the chassis in the cabinet, the other 3 undid easily. The rusted one sheared as I tried to turn it. When the chassis was removed I cut the remaining stub off flush with a Dremel and mini cutting disc and drilled through the centre of the old screw. All the other screws were the same self tapping type but the holes were tapped for 2 BA so I will be replacing them all with 2BA screws.
Next job will be tackling the capacitors, I dont expect to have to replace any resistors as this type used by KB are normally very accurate.
But that will be later as I am off to make use of the sunny weather to cut ply for another shelf.
Mike
