Fading on Philips B2G81U type radios - UK Vintage Radio Repair and Restoration Discussion Forum

telstar · 24th Jun 2013, 2:08 pm

Hi. I once read that some people had trouble with stations fading on these radios, occasionally requiring retuning. I found out that the tubular ceramic capacitor (c4 on service manual, value 0.022uF) had gone faulty, and although I do not have a stock of disc ceramic caps, a polyester type was installed in its place. Success, stability at last!
Cheers
Mike

Leon Crampin · 24th Jun 2013, 2:20 pm

Mike, to save us all looking it up, what's the circuit function of C4?

Leon.

telstar · 24th Jun 2013, 2:31 pm

Hi Leon. It is in the screen grid circuit of the UCH81 frequency changer. Most of the set uses the red ceramic types, but there are some grey ones of higher value that tend to get overlooked.
Cheers
Mike

Leon Crampin · 24th Jun 2013, 5:34 pm

Thanks, Mike.

telstar · 25th Jun 2013, 12:32 pm

Hi Leon. Yes, it is certainly worth replacing the higher value tubular ceramics, especially C4, the screen bypass for UCH81. It became an irritant trying to retune the radio every few minutes. I am doing the process of replacing these and out of tolerance resistors on the Philips B2G81U, Stella ST110U, & the Cossor.
Cheers
Mike

Tim · 26th Jun 2013, 12:19 am

I have always found those red "dog bone" capacitors above suspicion.
I have done three of these over the years and ALL had the same fault(or have had in the past). The UCL82 cathode resistor goes low on these sets, causing excess grid gurrent in the valve leading to all sorts of problems. Commonly the resistor(and occasionally the valve it's self) will have been replaced, usually with a larger power one, which then excasurbates the problem. Ht can dip, the valve can even go red hot sometimes-leading to fading. THe UCL82's in these sets have often had a traumatic life! I had one passing nearly 80mA. The grid capacitor is usually OK.

telstar · 26th Jun 2013, 3:54 pm

Hi. Changing these has made quite a difference to the set. Unfortunately, I do not have many modern ceramic replacements, so I have used the Polyester types, and the "Yellow" types as replacements.
Cheers
Mike

24th Jun 2013, 2:08 pm	#1
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,588	Fading on Philips B2G81U type radios Hi. I once read that some people had trouble with stations fading on these radios, occasionally requiring retuning. I found out that the tubular ceramic capacitor (c4 on service manual, value 0.022uF) had gone faulty, and although I do not have a stock of disc ceramic caps, a polyester type was installed in its place. Success, stability at last! Cheers Mike

24th Jun 2013, 2:20 pm	#2
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Fading on Philips B2G81U type radios Mike, to save us all looking it up, what's the circuit function of C4? Leon.

24th Jun 2013, 2:31 pm	#3
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,588	Re: Fading on Philips B2G81U type radios Hi Leon. It is in the screen grid circuit of the UCH81 frequency changer. Most of the set uses the red ceramic types, but there are some grey ones of higher value that tend to get overlooked. Cheers Mike

24th Jun 2013, 5:34 pm	#4
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Fading on Philips B2G81U type radios Thanks, Mike.

25th Jun 2013, 12:32 pm	#5
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,588	Re: Fading on Philips B2G81U type radios Hi Leon. Yes, it is certainly worth replacing the higher value tubular ceramics, especially C4, the screen bypass for UCH81. It became an irritant trying to retune the radio every few minutes. I am doing the process of replacing these and out of tolerance resistors on the Philips B2G81U, Stella ST110U, & the Cossor. Cheers Mike

26th Jun 2013, 12:19 am	#6
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,307	Re: Fading on Philips B2G81U type radios I have always found those red "dog bone" capacitors above suspicion. I have done three of these over the years and ALL had the same fault(or have had in the past). The UCL82 cathode resistor goes low on these sets, causing excess grid gurrent in the valve leading to all sorts of problems. Commonly the resistor(and occasionally the valve it's self) will have been replaced, usually with a larger power one, which then excasurbates the problem. Ht can dip, the valve can even go red hot sometimes-leading to fading. THe UCL82's in these sets have often had a traumatic life! I had one passing nearly 80mA. The grid capacitor is usually OK. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

26th Jun 2013, 3:54 pm	#7
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,588	Re: Fading on Philips B2G81U type radios Hi. Changing these has made quite a difference to the set. Unfortunately, I do not have many modern ceramic replacements, so I have used the Polyester types, and the "Yellow" types as replacements. Cheers Mike