10-09-2016, 08:03 PM
An excellent day today, despite the constant drizzle - it could have been much worse!
Never seen so many old sets working together before. Some had to be turned off mid-afternoon when the conduit carrying the incoming mains was found to be getting rather hot!
I noticed a Sobell with a pronounced switch off spot after this. It obviously uses the on/off switch for switch off spot suppression* but this doesn't work when the mains supply is interrupted externally. It might be a good idea to modify it to an alternative method of suppression to protect the tube.
* I assume it uses the method whereby the earthy end of the brightness control circuit is returned to the mains input side of the switch. With the switch on it is, of course, connected to the chassis but, when it is switched off the circuit floats effectively turning the brightness up full so as to discharge the EHT quickly while the scan is collapsing.
Never seen so many old sets working together before. Some had to be turned off mid-afternoon when the conduit carrying the incoming mains was found to be getting rather hot!
I noticed a Sobell with a pronounced switch off spot after this. It obviously uses the on/off switch for switch off spot suppression* but this doesn't work when the mains supply is interrupted externally. It might be a good idea to modify it to an alternative method of suppression to protect the tube.
* I assume it uses the method whereby the earthy end of the brightness control circuit is returned to the mains input side of the switch. With the switch on it is, of course, connected to the chassis but, when it is switched off the circuit floats effectively turning the brightness up full so as to discharge the EHT quickly while the scan is collapsing.
