|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
4th Dec 2017, 11:14 am | #1 |
Heptode
Join Date: Sep 2007
Location: Brentwood, Essex, UK.
Posts: 687
|
GEC BC 4750 Fault
Hello All,
I am getting a strange fault on this GEC BC4750 that I wondered if anyone else had experienced. I changed the faulty HT Smoothing and output valve grid coupling caps and powered it up, even without an aerial it was getting the strongest MW Stations quite well - this is going to be an easy one I thought (mistake) The weird thing is connecting up the usual 15ft of wire that I use actually makes reception worse, or at best on some stations a very slight improvement, on many it drops the volume level. I noticed by accident that a finger, or the length of wire, touched on the SW Aerial trimmer (C26 on trader sheet 919 ) makes reception quite good on MW with plenty of volume. I thought possibly switching problems so have cleaned the wave change switches with no improvement. I think I had something similar with a GEC BC4850 years ago and never found out what it was! Cheers, Steve. |
4th Dec 2017, 12:30 pm | #2 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
|
Re: GEC BC 4750 Fault
It could be a high resistance connection or short on one of the trimmer capacitors.
Try moving the adjustment screw and then return it to the original position. |
4th Dec 2017, 12:31 pm | #3 |
Nonode
Join Date: Dec 2012
Location: Bocking, near Braintree, Essex, UK.
Posts: 2,068
|
Re: GEC BC 4750 Fault
Hi Steve
it might be worth checking to see if any of the wafer switches have defective contacts and some of the coupling and de-coupling capacitors. I personally have not come across this with sets but there it is. Best wishes Ken |
4th Dec 2017, 1:05 pm | #4 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: GEC BC 4750 Fault
Yes, change ALL the paper dielectric capacitors. They will all be leaky to a greater or lesser degree. Leaky decouples can alter the DC conditions on valves causing various symptoms and the AGC function can also be defeated by leaky capacitors.
I always change all the paper capacitors in a set and they always test leaky at their working voltage. |