SONY KV 1810 - MOV's on On/Off switch - UK Vintage Radio Repair and Restoration Discussion Forum

simpsons · 30th Sep 2018, 11:10 am

I have a couple of KV1810, with different presentation, which I wish to protect the mains on/off switch from sparking and ultimately blowing the SGS.

Sony have used Metal Oxide Varistors on their mains switches for various sets part KC103p which begs the question would it be a good idea to include them in the 1810.

Sony place them across each of the contacts ie not across the switched supply.

Any help to keep my beasts tamed would be welcomed.

Chris

Studio263 · 30th Sep 2018, 12:16 pm

Personally I wouldn't. These sets should be reliable if everything is as per the original spec and in good condition.

The real issue is the line oscillator. It must start promptly when the power is applied and run on for a little time when it is switched off. There are a few small electrolytics on the power supply panel to keep and eye on too, and I always removed the line hold control and fitted a fixed resistor instead. Like this, I have found the KV-1810UB to be a reliable television, until the tube goes flat in any case...

There was a big fuss about these when they were new but now everyone is used to switch mode converters that blow up when a few silly electrolytic capacitors get mouldy there really isn't too much to get excited about. 'Television' published some good conversions to use normal transistors; the one which used the Rank A823 line driver transformer was possibly the easiest one to do.

A few points of caution to newcomers to these sets: Never attempt to start them up with a variac or a lamp limiter; that will ruin the whole lot straight away even if the set is (was...) fault-free. For a soft start-up, the 18V line must be established first using an external power supply. Then you can bring the mains voltage up gently, although you will get clouds of smoke from the resistors in the start-up circuit if you dawdle over it.

30th Sep 2018, 11:10 am	#1
simpsons Octode Join Date: Feb 2007 Location: Harrow, London, UK. Posts: 1,493	SONY KV 1810 - MOV's on On/Off switch I have a couple of KV1810, with different presentation, which I wish to protect the mains on/off switch from sparking and ultimately blowing the SGS. Sony have used Metal Oxide Varistors on their mains switches for various sets part KC103p which begs the question would it be a good idea to include them in the 1810. Sony place them across each of the contacts ie not across the switched supply. Any help to keep my beasts tamed would be welcomed. Chris

30th Sep 2018, 12:16 pm	#2
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,578	Re: SONY KV 1810 - MOV's on On/Off switch Personally I wouldn't. These sets should be reliable if everything is as per the original spec and in good condition. The real issue is the line oscillator. It must start promptly when the power is applied and run on for a little time when it is switched off. There are a few small electrolytics on the power supply panel to keep and eye on too, and I always removed the line hold control and fitted a fixed resistor instead. Like this, I have found the KV-1810UB to be a reliable television, until the tube goes flat in any case... There was a big fuss about these when they were new but now everyone is used to switch mode converters that blow up when a few silly electrolytic capacitors get mouldy there really isn't too much to get excited about. 'Television' published some good conversions to use normal transistors; the one which used the Rank A823 line driver transformer was possibly the easiest one to do. A few points of caution to newcomers to these sets: Never attempt to start them up with a variac or a lamp limiter; that will ruin the whole lot straight away even if the set is (was...) fault-free. For a soft start-up, the 18V line must be established first using an external power supply. Then you can bring the mains voltage up gently, although you will get clouds of smoke from the resistors in the start-up circuit if you dawdle over it.