This radio is proving to be very troublesome. What with the slipping tuning drive, which apart from the issue of the balance of the moving vanes is also caused by irregularities in the bearing cup bearing face, causing unwanted movement and sticking of the balls. I think It will require a new bearing cup to be made.
Apart from that I have the issue with LW. If I stop breathing then I can just about hear and tune in R4 but the tuning seems to wander.
My assumptions were that as I can JUST tune it in there must be a problem in the aerial circuits. There are very few fixed capacitors involved with the tuning of this radio they are all mostly trimmer capacitors. I have checked all the trimmer capacitors and they seem to measure OK and the capacitance changes slightly if I turn the nuts one way and then the other.
So it leaves me to think the fault lies in the aerial and or the bandpass coils. Resistance measurements confirm an possible issue with the aerial coil between tags I & E it is listed as 0 ohms but the reading is 8.4 ohms.
Question. Would you expect to see a resistance of 0 ohms on that part of the coil, is it not the LW section of the primary as it appears to be bypassed when switched for MW reception. Could the figure 0 be a misprint?
(switches 1 to 6 are all closed for MW, and only 4 & 5 are closed for LW)
Since measurements of the RF coils I decided to measure the oscillator coils, and found a problem there also on one of the LW windings. The resistance between tags K & H is infinity it is listed as 14 ohms. Could be the cause of the problem with LW, where it can tune R4 but only audible if I hold my breath.
It appears that the aluminium cans are fixed to the chassis somehow, possibly with a rolled rim, and the coil former assembly is removed from the can by pulling down though the chassis, so a lot of other parts will need to be removed in order to make a clear space for the cols to be pulled through with out risk of further damage.
I have had a look at quite a few other KB models schematics and there are not any others which use this particular aerial coil, most other designs use a 3 coil assembly.
I would really appreciate your thoughts please before I perform major surgery and try and extract the coils from the chassis.
Mike
Apart from that I have the issue with LW. If I stop breathing then I can just about hear and tune in R4 but the tuning seems to wander.
My assumptions were that as I can JUST tune it in there must be a problem in the aerial circuits. There are very few fixed capacitors involved with the tuning of this radio they are all mostly trimmer capacitors. I have checked all the trimmer capacitors and they seem to measure OK and the capacitance changes slightly if I turn the nuts one way and then the other.
So it leaves me to think the fault lies in the aerial and or the bandpass coils. Resistance measurements confirm an possible issue with the aerial coil between tags I & E it is listed as 0 ohms but the reading is 8.4 ohms.
Question. Would you expect to see a resistance of 0 ohms on that part of the coil, is it not the LW section of the primary as it appears to be bypassed when switched for MW reception. Could the figure 0 be a misprint?
(switches 1 to 6 are all closed for MW, and only 4 & 5 are closed for LW)
Since measurements of the RF coils I decided to measure the oscillator coils, and found a problem there also on one of the LW windings. The resistance between tags K & H is infinity it is listed as 14 ohms. Could be the cause of the problem with LW, where it can tune R4 but only audible if I hold my breath.
It appears that the aluminium cans are fixed to the chassis somehow, possibly with a rolled rim, and the coil former assembly is removed from the can by pulling down though the chassis, so a lot of other parts will need to be removed in order to make a clear space for the cols to be pulled through with out risk of further damage.
I have had a look at quite a few other KB models schematics and there are not any others which use this particular aerial coil, most other designs use a 3 coil assembly.
I would really appreciate your thoughts please before I perform major surgery and try and extract the coils from the chassis.
Mike
