Been contemplating how to title this topic.. But ..some lessons learnt here to share and advice needed please. The darling Marantz 2215 (not the b model) ...with the bulk of its amp board populated with Carbon Composite resistors is known for its warm valve like sound due to these resistors. (scientific explanations about this resistors unique current flow/handling, temp co-efficient, breakdown modes, aging issues, tolerance and surge capabilities aside as it would make this a mammoth post). Its now round 3...venturing into this receiver...round 1 was a recap...round 2 was replacement of 2 output transistors due to a tiny slip up :facepalm:....and round 3....i drove a predominantly capacitive load and burnt the same set of outputs on a channel as in round 2. ( I use this as my low power test amp so its always at risk 
) Im now at a point where i have identified 2 problems....1). I used an over-rated power emitter (3 or 5 watts) resistor in round 2 and it didnt go into its safety mode which needed to start at 2 watts rating. 2). The over-current sensing cc 10% resistors are measuring at 13% at ambient temp...so what should be 680 ohms is testing at 762ohms..and not affording the protection needed..when its needed & being out of spec..in operation..temp/current can send them haywire. I can sort that with carbon 5% carbon films, but beg an answer ...what was Marantz doing with 10% tolerance in this position and how critical is this..5% was available then....if i use 5% here, would i be over-compensating or should i use a slightly higher value cf here to compensate for the variance of the 10% cc in some way? How can i test this overload protection? ////// secondly, the required emitter resistor type on a power trannie ? It had 2w 0.5ohm M2 resistors...encased in a cylindrical ceramic casing...rated 2w at 98 degrees. Theres a derating scale applicable here obviously. I need a resistor in this position to fail safely in an open position without any fire...and the Vishay Pr02 seems a likely candidate....but wary that they can run to 4w before starting self-destruction. A wirewound also can run until fire status...carbons are not suitable here apparently. Im left with Pr02 power metal films...which run to 250 deg...and can allow up to 4w...which will kill my outputs again. So what do i use here ? ...I understand that the primary problem causing this issue was the protection cct...but now need to choose suitable 2w emitter resistors. Thanks guys...sorry for the long post.
) Im now at a point where i have identified 2 problems....1). I used an over-rated power emitter (3 or 5 watts) resistor in round 2 and it didnt go into its safety mode which needed to start at 2 watts rating. 2). The over-current sensing cc 10% resistors are measuring at 13% at ambient temp...so what should be 680 ohms is testing at 762ohms..and not affording the protection needed..when its needed & being out of spec..in operation..temp/current can send them haywire. I can sort that with carbon 5% carbon films, but beg an answer ...what was Marantz doing with 10% tolerance in this position and how critical is this..5% was available then....if i use 5% here, would i be over-compensating or should i use a slightly higher value cf here to compensate for the variance of the 10% cc in some way? How can i test this overload protection? ////// secondly, the required emitter resistor type on a power trannie ? It had 2w 0.5ohm M2 resistors...encased in a cylindrical ceramic casing...rated 2w at 98 degrees. Theres a derating scale applicable here obviously. I need a resistor in this position to fail safely in an open position without any fire...and the Vishay Pr02 seems a likely candidate....but wary that they can run to 4w before starting self-destruction. A wirewound also can run until fire status...carbons are not suitable here apparently. Im left with Pr02 power metal films...which run to 250 deg...and can allow up to 4w...which will kill my outputs again. So what do i use here ? ...I understand that the primary problem causing this issue was the protection cct...but now need to choose suitable 2w emitter resistors. Thanks guys...sorry for the long post.
