Fusible (metal) resistors in Hitachi int. amp (carbon replacements okay)
I just purchased an early 80s Hitachi HA-4700 that's quite a mess in the pwr-amp section.
Not sure what happened to this amp? Evil spirits. Lightning strike. Or multiple attempts by former user (abuser!!) using shorted loudspeakers???
Both output transistors in Right channel were shorted, several related driver transistors also bad. Not sure what happened. It did power up and all the "lights came on" and main fuse okay.
The pwr-amp board has several metal-film fusible resistors (raised legs on PCB), and some are in signal path. Not sure why they are metal film (so they open faster for fuse protection???) . All are 1/4 W.
Many were open or very high in value (from 82 ohm, heat damaged to above 2k-ohm, etc). And several in Left channel, also, which still had output and driver transistors intact!
All I have are same value carbons. Any reason to be concerned here? FYI : I am going to be the sole owner of this HA-4700 henceforth. And I won't abuse it and I never play amps loud.
Posted Oct 5, 2024, 7:45 AM UTC