Philips B3G85U very loud hum - UK Vintage Radio Repair and Restoration Discussion Forum

Mike Noble · 17th Sep 2008, 10:24 pm

While warming up the hum gets so loud that you have to turn it off and the volume control makes no difference. Sounds like 50Hz.
Where should I start? No caps changed yet and everything looks original.
Thanks, Mike.

Steve_P · 17th Sep 2008, 10:30 pm

Capacitors first. C49 of course.

If the hum is 50 Hz and not affected by volume, then are the smoothers OK - C1 and C2 are in a large can. C50 is another possibility.

Cheers,

Steve P.

Sideband · 17th Sep 2008, 10:33 pm

Quote:

Originally Posted by Mike Noble

No caps changed yet and everything looks original. Thanks, Mike.

That'll be the problem then! If the set hasn't been used for ages, the electrolytics will need reforming, if it has been used then they probably want replacing. Don't run it any more without replacing the audio coupling capacitor. If the set has got those big tar-covered black capacitors that Philips favoured, these will probably all need replacing. See the recent thread on capacitors for some good advice.

Rich.

Tim · 17th Sep 2008, 11:53 pm

Hi Mike.
I have found the smoothing capacitors in most Philips sets to be very poor so I wouldn't be in the least bit surprised if the above diagnoses are found to be correct. I have one of these and the HT smoothers are knackered on that one too. These are pleasing sets when going.

Mike Noble · 18th Sep 2008, 7:23 am

Thanks, I'll try the smoothing caps and replace the black encapsulated type (only two) and see what happens.
I have restored a few radios now but have never had one where the hum is so loud. So loud you have to turn it off before reaching full volume.
Thanks, Mike.

17th Sep 2008, 10:24 pm	#1
Mike Noble Pentode Join Date: Oct 2005 Location: Harlow, Essex, UK. Posts: 162	Philips B3G85U very loud hum While warming up the hum gets so loud that you have to turn it off and the volume control makes no difference. Sounds like 50Hz. Where should I start? No caps changed yet and everything looks original. Thanks, Mike. Last edited by Mike Noble; 17th Sep 2008 at 10:24 pm. Reason: No manufacturer specified.

17th Sep 2008, 10:30 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Philips B3G85U very loud hum Capacitors first. C49 of course. If the hum is 50 Hz and not affected by volume, then are the smoothers OK - C1 and C2 are in a large can. C50 is another possibility. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

17th Sep 2008, 11:53 pm	#4
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Philips B3G85U very loud hum Hi Mike. I have found the smoothing capacitors in most Philips sets to be very poor so I wouldn't be in the least bit surprised if the above diagnoses are found to be correct. I have one of these and the HT smoothers are knackered on that one too. These are pleasing sets when going. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

18th Sep 2008, 7:23 am	#5
Mike Noble Pentode Join Date: Oct 2005 Location: Harlow, Essex, UK. Posts: 162	Re: Philips B3G85U very loud hum Thanks, I'll try the smoothing caps and replace the black encapsulated type (only two) and see what happens. I have restored a few radios now but have never had one where the hum is so loud. So loud you have to turn it off before reaching full volume. Thanks, Mike.