Replacement tremolo optocoupler, also known as a "roach" was used in vintage Fender amps. It can also be used to upgrade certain modern Fenders.

Gold dot indicates neon bulb connection side.

This type of optocoupler tremolo circuit was used by Fender from the mid 60's when they introduced the Blackface range of amps, and this circuit is used in most Blackface and Silverface models (the exceptions being the Vibro Champ and Princeton models).

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