PBM8 500 MKII Fault Solved!

When an amplifier is overloaded, usually some transistors go short; their power resistors go open, and the fuse blows. The PBM8-500 MKII tends to also follow these classic symptoms.

"It's these Klingon crystals captain... they're completely drained."

Some of the Church volunteers took the amp for a party celebration and decided to connect some of their own speakers to it. They plugged the amp into a speaker array, causing an overload, however this is actually a very good amplifier considering it lasted for so many years taking the abuse.

Power Resistor Modification

In this amplifier, the large metal film leaded resistors have a 3-watt power rating; whilst the smaller ones connected to the MJE pair have a 2-watt power rating. Although similar replacements would work, I figured that I would need something meaner to rock the pillars of the Church; hence, I used 5-watt replacements. These resistors should be able to withstand the full volume output in total comfort.

This photograph shows one channel, however, I replaced the resistors on both channels, so that the power output was identical from both channels.

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