Sobellette 439 distortion - UK Vintage Radio Repair and Restoration Discussion Forum

petervk2mlg · 8th Jun 2018, 11:40 am

I have serviced my Sobellette by replacing leaky capacitors and out of tolerance resistors. The radio works well with the volume control well advanced, but I notice that when I back the volume control off significant distortion is evident.
In this radio the volume pot varies the screen voltage of the first valve - a type 14S7.
The screen voltage at maximum is 83 volts and distortion becomes apparent with the control retarded and the screen voltage at 25 volts. It gets worse as the pot is backed off further.
I wonder if there is anything to be done to improve matters.
Peter

Cobaltblue · 8th Jun 2018, 12:58 pm

Hi Peter

I never really noticed the distortion on mine but then I wasn't expecting much anyway

But it seems its a common problem https://www.vintage-radio.com/recent...bell-1950.html

Cheers

Mike T

Boater Sam · 8th Jun 2018, 1:48 pm

Lateral, Speaker? Some foul until the volume is increased.

petervk2mlg · 8th Jun 2018, 2:21 pm

Quote:

Originally Posted by Cobaltblue

Hi Peter

I never really noticed the distortion on mine but then I wasn't expecting much anyway

But it seems its a common problem https://www.vintage-radio.com/recent...bell-1950.html

Cheers

Mike T

Thanks Mike. Interesting.

petervk2mlg · 8th Jun 2018, 2:21 pm

Quote:

Originally Posted by Boater Sam

Lateral, Speaker? Some foul until the volume is increased.

I'm pretty sure the speaker cone is moving freely.

8th Jun 2018, 11:40 am	#1
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	Sobellette 439 distortion I have serviced my Sobellette by replacing leaky capacitors and out of tolerance resistors. The radio works well with the volume control well advanced, but I notice that when I back the volume control off significant distortion is evident. In this radio the volume pot varies the screen voltage of the first valve - a type 14S7. The screen voltage at maximum is 83 volts and distortion becomes apparent with the control retarded and the screen voltage at 25 volts. It gets worse as the pot is backed off further. I wonder if there is anything to be done to improve matters. Peter

8th Jun 2018, 12:58 pm	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,863	Re: Sobellette 439 distortion Hi Peter I never really noticed the distortion on mine but then I wasn't expecting much anyway But it seems its a common problem https://www.vintage-radio.com/recent...bell-1950.html Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

8th Jun 2018, 1:48 pm	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Sobellette 439 distortion Lateral, Speaker? Some foul until the volume is increased.