throbscottle
Well-Known Member
I'm repairing my 'scope again. Found a couple of resistors gone high feeding the focus control. The control isn't affected so I'm leaving them in place for now, but I want to understand why they used the combination they did.
The design dates from late '60's so please bear this in mind.
The 2 resistors are in series and probably have about 1kV across them. One is carbon composition, the other I'm not sure what it's made of - carbon or metal film I think - it's unlike any other resistor in the 'scope, long and narrow. The composition one should be 330K and the possibly film one should be 470K, so 800K in total. The 330K is the only composition resistor in the 'scope. I think they're both original but I'm not sure. Most of the others are carbon film.
Any suggestions why these types of resistor would have been used? I'm thinking maybe the tempco's cancel out, but why bother here? It's working happily with over 1meg where it should be 800K.
The design dates from late '60's so please bear this in mind.
The 2 resistors are in series and probably have about 1kV across them. One is carbon composition, the other I'm not sure what it's made of - carbon or metal film I think - it's unlike any other resistor in the 'scope, long and narrow. The composition one should be 330K and the possibly film one should be 470K, so 800K in total. The 330K is the only composition resistor in the 'scope. I think they're both original but I'm not sure. Most of the others are carbon film.
Any suggestions why these types of resistor would have been used? I'm thinking maybe the tempco's cancel out, but why bother here? It's working happily with over 1meg where it should be 800K.