Early D-150A fuses?

jackospax

Hello, I'm working on an early 4-amp D-150A that does not have the ioc lights. Exactly what type of fuses does it use? Slow or fast-blow is what I need to know. Thanks!

scytech

Depends! What was the current failure? Meaning, was it a transitory failure or hard core?
By transitory, does this failure happen often? Does the fuse appear 'fused' or exploded, black? If it's exploded or black, a catastrophic event happened. It will happen again, so slow or fast won't resolve issue. If it only fused, that may mean a transitory event happened, and the fuse caught the event. If a fast acting fuse was previously used then a slow acting fuse could be used, with caution.
We also would need to find out what caused the event. If it came from the power supply, an over current condition can be caused by an over exertion of the power amp above clipping. Clipping is notorious for blowing up amps, if the condition persists long enough! Heat causes thermal runaway and can damage output devices; so heatsinking is important.
Make sure there is adequate thermal isolation paste on output device.
Make sure fans and ducts are absent of debris, dust foams cleaned and properly ventilated (not for the D150!). Make sure speaker impedances are within specs. Fuse failures happen because of a too low impedance network, that needs a lot of current!
Check and adjust output bias setting for proper signal generation.