Capacitor question - UK Vintage Radio Repair and Restoration Discussion Forum

ekcopyephilips · 23rd Dec 2013, 2:35 pm

Hi all

Just doing a shopping list to replace the critical capacitors on the printed line panel on the PYE 697 chassis.
according to the service manual different capacitors are used, a mix of ceramic, polyester and polystyrene. Can the two be easily mixed about? Or do Ii have to make sure that a ceramic is replaced by a ceramic?

Is there a good mix of ranges and voltages Ii should be buying, and where from?

Mike

G8HQP Dave · 23rd Dec 2013, 4:35 pm

Best to stick to the type specified by the manufacturer, except where you can determine what the requirements are and can judge which alternatives will do.

Lucien Nunes · 23rd Dec 2013, 9:45 pm

Polystyrene is often chosen for tight tolerance and good stability e.g. in oscillators and tuned circuits, best replace like with like. Polyester is a general purpose low-cost dielectric, can sometimes be replaced with (e.g.) polypropylene for improved reliability in high-stress applications although PP caps are larger. Ceramics are often chosen for low inductance and/or specific temperature coefficients (in the smaller values e.g. in filters) and should be replaced with ceramic of the same grade.

Generally, replacing a capacitor with one of suitable rating but unsuitable construction or dielectric, will result in a circuit that works but with reduced performance, reliability or stability.

23rd Dec 2013, 2:35 pm	#1
ekcopyephilips Hexode Join Date: Dec 2006 Location: Norwich, Norfolk, UK. Posts: 440	Capacitor question Hi all Just doing a shopping list to replace the critical capacitors on the printed line panel on the PYE 697 chassis. according to the service manual different capacitors are used, a mix of ceramic, polyester and polystyrene. Can the two be easily mixed about? Or do Ii have to make sure that a ceramic is replaced by a ceramic? Is there a good mix of ranges and voltages Ii should be buying, and where from? Mike

23rd Dec 2013, 4:35 pm	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Capacitor question Best to stick to the type specified by the manufacturer, except where you can determine what the requirements are and can judge which alternatives will do.

23rd Dec 2013, 9:45 pm	#3
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Capacitor question Polystyrene is often chosen for tight tolerance and good stability e.g. in oscillators and tuned circuits, best replace like with like. Polyester is a general purpose low-cost dielectric, can sometimes be replaced with (e.g.) polypropylene for improved reliability in high-stress applications although PP caps are larger. Ceramics are often chosen for low inductance and/or specific temperature coefficients (in the smaller values e.g. in filters) and should be replaced with ceramic of the same grade. Generally, replacing a capacitor with one of suitable rating but unsuitable construction or dielectric, will result in a circuit that works but with reduced performance, reliability or stability.