UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - KB FB10

boxdoctor · 9th Jan 2019, 5:49 pm

A friend has presented me with his FB10 to fix for him. It has been out of use for well over 20 years, and, to start with, the dial drive cord had decayed to the point where it had come apart.
I replaced this with some fishing line as recommended in the service sheet, and upon trying the set, I had faint audio with some distortion. Cutting a long story short, the output valve holder was carbonised and leaky. I carefully drilled it out and fitted a ceramic one in the paxolin "factory bodge" panel which incorporated the original holder. Somewhat better results ensued, but the tuning seemed broad compared with the FB10 which I have in the kitchen. Sensitivity is below par as well. All waxies etc. have been replaced.
I thought to check the I.F.s, and found that they were aligned on 465 Khz rather than the service manual's 422Khz. recommendation.
Has anybody come across this before, i.e. was there a known production batch with 465Khz I.F.s? Or has the phantom twiddler been at work. The audio coupling cap has been replaced at some time.
I dont want to disturb the I.F.s unless necessary, as they have the dreadful paxolin threads to hold the cores in position, which I know from experience are very brittle and delicate. Tony.

9th Jan 2019, 5:49 pm	#1
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	KB FB10 - I.F. frequency query. A friend has presented me with his FB10 to fix for him. It has been out of use for well over 20 years, and, to start with, the dial drive cord had decayed to the point where it had come apart. I replaced this with some fishing line as recommended in the service sheet, and upon trying the set, I had faint audio with some distortion. Cutting a long story short, the output valve holder was carbonised and leaky. I carefully drilled it out and fitted a ceramic one in the paxolin "factory bodge" panel which incorporated the original holder. Somewhat better results ensued, but the tuning seemed broad compared with the FB10 which I have in the kitchen. Sensitivity is below par as well. All waxies etc. have been replaced. I thought to check the I.F.s, and found that they were aligned on 465 Khz rather than the service manual's 422Khz. recommendation. Has anybody come across this before, i.e. was there a known production batch with 465Khz I.F.s? Or has the phantom twiddler been at work. The audio coupling cap has been replaced at some time. I dont want to disturb the I.F.s unless necessary, as they have the dreadful paxolin threads to hold the cores in position, which I know from experience are very brittle and delicate. Tony.