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).
Any questions, feel free to message me!