Pye CR/AC tone control help required - UK Vintage Radio Repair and Restoration Discussion Forum

lloydwells · 30th Sep 2019, 6:46 pm

Ive nearly finished my PYE CR/AC however the variable condenser that actsbas a tone control is dead does anyone know the value of this as its not on the schematic

PJL · 30th Sep 2019, 8:55 pm

In what way is it dead? I would expect to be able to repair something that age.

Herald1360 · 30th Sep 2019, 10:32 pm

Any variable condenser is unlikely to be greater than perhaps 1000pF max and more likely to be around 500pF.

Looking at the circuit it's a bit of a guess what the signal source impedance of the secondary of T3 might be, but if it's around 100k, 500pF would give -3dB at about 3kHz so maybe a plausible value.

Easy enough just to hook up a typical tuning capacitor of 500pF or so and see what effect it has.

Whatever the value, a suitable result could be obtained with something like a 1n capacitor in series with perhaps a 470k log variable resistor in place of the capacitor.

lloydwells · 1st Oct 2019, 8:43 am

PJL half of its missing however if you have the ability to raise the dead thats handy ;-)

30th Sep 2019, 6:46 pm	#1
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 550	Pye CR/AC tone control help required Ive nearly finished my PYE CR/AC however the variable condenser that actsbas a tone control is dead does anyone know the value of this as its not on the schematic

30th Sep 2019, 8:55 pm	#2
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Pye CR/AC tone control help required In what way is it dead? I would expect to be able to repair something that age.

30th Sep 2019, 10:32 pm	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Pye CR/AC tone control help required Any variable condenser is unlikely to be greater than perhaps 1000pF max and more likely to be around 500pF. Looking at the circuit it's a bit of a guess what the signal source impedance of the secondary of T3 might be, but if it's around 100k, 500pF would give -3dB at about 3kHz so maybe a plausible value. Easy enough just to hook up a typical tuning capacitor of 500pF or so and see what effect it has. Whatever the value, a suitable result could be obtained with something like a 1n capacitor in series with perhaps a 470k log variable resistor in place of the capacitor. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

1st Oct 2019, 8:43 am	#4
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 550	Re: Pye CR/AC tone control help required PJL half of its missing however if you have the ability to raise the dead thats handy ;-)