Philips G4H G4L B4S51A/13 - UK Vintage Radio Repair and Restoration Discussion Forum

RubberGloves · 7th Oct 2018, 7:17 pm

Evening folks,

I joined the forum a couple of weeks ago and received some great advice that allowed me to fix my old 1 inch oscilloscope - turned out to be a simplified British National Radio School Learnakit scope, rather than a Mullard Pupil/Student scope as I had incorrectly presumed - anyway, fixed now, so thanks chaps!

Also just managed to fix my old Philips radio. I bought it circa 2010 and it worked well for 2 or 3 years before failing when it had been running for a couple of hours. It started harshly motor-boating and there was a worrying smell, so I switched it off. Was busy fixing the motorbike at the time and I should have looked inside, but didn't have time. Foolishly tried it again the next day and there was no life, just the heaters and lamps lit.

Anyway, fairly simple faults and managed to fix it -
C57 0.01u on the speaker output EL86 had gone totally short and melted. This had overheated its series resistor R48 3k3 which now read only 100 Ohms! Also noticed that R50 47R feeding the anode from the output transformer had been very hot and had gone totally open circuit (fortunately!). Fixing these three brought the anode HT back to the EL86, but still no life. Then noticed that R35 680R on the opposite end of the output transformer primary (feeding most of the other HT) had gone translucent pink in colour. This had also gone totally open circuit (fortunately again!), although it gave a helluva splat when I touched it with a plastic probe (must have momentarily fixed the open circuit!

Anyway, now working fine. And somehow the output transformer lived to tell the tale!

Circuit schematic attached - may help with trickier faults!

Cheers,

Rob.

7th Oct 2018, 7:17 pm	#1
RubberGloves Retired Dormant Member Join Date: Sep 2018 Location: Clacton-on-Sea, Essex, UK. Posts: 7	Philips G4H G4L B4S51A/13 Evening folks, I joined the forum a couple of weeks ago and received some great advice that allowed me to fix my old 1 inch oscilloscope - turned out to be a simplified British National Radio School Learnakit scope, rather than a Mullard Pupil/Student scope as I had incorrectly presumed - anyway, fixed now, so thanks chaps! Also just managed to fix my old Philips radio. I bought it circa 2010 and it worked well for 2 or 3 years before failing when it had been running for a couple of hours. It started harshly motor-boating and there was a worrying smell, so I switched it off. Was busy fixing the motorbike at the time and I should have looked inside, but didn't have time. Foolishly tried it again the next day and there was no life, just the heaters and lamps lit. Anyway, fairly simple faults and managed to fix it - C57 0.01u on the speaker output EL86 had gone totally short and melted. This had overheated its series resistor R48 3k3 which now read only 100 Ohms! Also noticed that R50 47R feeding the anode from the output transformer had been very hot and had gone totally open circuit (fortunately!). Fixing these three brought the anode HT back to the EL86, but still no life. Then noticed that R35 680R on the opposite end of the output transformer primary (feeding most of the other HT) had gone translucent pink in colour. This had also gone totally open circuit (fortunately again!), although it gave a helluva splat when I touched it with a plastic probe (must have momentarily fixed the open circuit! Anyway, now working fine. And somehow the output transformer lived to tell the tale! Circuit schematic attached - may help with trickier faults! Cheers, Rob. Attached Thumbnails