What is this??

[pineapple49]

What is this? it is from a Fender Showman Schematic, and what is it called, i have seen them in all fender schematics

[Robert M. Martinelli]

It' s an LDR ( Light Dependent Resistor ), the little portion of the schematic you uploaded does not show its "surroundings", but usually, in guitar amps, LDRs can be found in the vibrato/tremolo section - the resistor on the right changes its value depending on the light intensity of the lamp on the left, ( the ellipse around the lamp and the resistor means they' re both contained in the same envelope ) so it's both called an opto-isolator ( because it isolates electrically one stage from another ) or an opto-coupler ( because it couples the two stages optically ). Visually it looks like a black bug with four legs, this is the reason why some amp techs call it "trem roach".
Hope this helps
Best regards
Bob

[tboy]

Well, you won't find one in every Fender amp; only models with tremolo have them. It's an opto-isolator, often called the "tremolo roach" because of it's resemblance to a small bug. It consists of a neon lamp and a photocell squished together inside a short length of heat-shrink tubing, with their leads sticking out the ends. The lamp is driven by the tremolo oscillator, and it's varying intensity of light causes a corresponding change in the resistance of the photocell, which acts as one leg of a voltage divider and thus varies the intensity of the audio signal.

[pineapple49]

Thankyou very Much

[mac1amps]

'just a minor footnote. These photocell/neon lamp assemblies are in all "Blackface" and later Fender models with [as Fender called it] Vibrato (even though technically, it's tremolo). On prior models, Fender used a "modulation" tube stage, without the photo/ neon "roach".