mikeyB
Well-known member
Any help from the guru's much appreciated!!
Studio I service has a faulty EMT 140 with V54 valve control gear. Nasty great mains hum after power up!! Mused over the innards for a while and all looked well, then noticed the big 50u + 50u on the mains filter had a "salty wart" on the can! Scraped this away to see a little puncture in the can. Replaced with a new 50u + 50u 500V cap, but same nasty hum persists. Turned my attention to bridge rectifier - this is a selenium B300C70 - trolled web and saw on a vintage hifi site that these go high resistance over time and can be replaced with silicon bridge but may need a dropper resistance to compensate for different rectifier diodes. Can't find any datasheet for said rectifier - has anyone got a datasheet or info regarding voltage drop across selenium bridge B300C70? Hifi site went on to say that left in this condition may damage hard to find tubes (****! - this has 2 telefunken EF804s' in it!) and damage to transformers may result (GULP!) - hopefully this hasn't occurred yet!! - but the unit is in a remote insulated room left permanently powered to stabilise the room temperature.
Any comments/help/advice welcome with thanks in advance!!
Studio I service has a faulty EMT 140 with V54 valve control gear. Nasty great mains hum after power up!! Mused over the innards for a while and all looked well, then noticed the big 50u + 50u on the mains filter had a "salty wart" on the can! Scraped this away to see a little puncture in the can. Replaced with a new 50u + 50u 500V cap, but same nasty hum persists. Turned my attention to bridge rectifier - this is a selenium B300C70 - trolled web and saw on a vintage hifi site that these go high resistance over time and can be replaced with silicon bridge but may need a dropper resistance to compensate for different rectifier diodes. Can't find any datasheet for said rectifier - has anyone got a datasheet or info regarding voltage drop across selenium bridge B300C70? Hifi site went on to say that left in this condition may damage hard to find tubes (****! - this has 2 telefunken EF804s' in it!) and damage to transformers may result (GULP!) - hopefully this hasn't occurred yet!! - but the unit is in a remote insulated room left permanently powered to stabilise the room temperature.
Any comments/help/advice welcome with thanks in advance!!
