Electronic – What does this resistor symbol mean

resistorssymbol [~]

While repairing a Marantz amplifier using the service manual, I came across resistors with odd symbols (see page 18).
They are trapped between two parallel lines (for example, 3297).

Is this linked to the fact that this is a 0.33W resistor? A comment suggested it could be related to the way it's mounted to the board for heat dissipation, but I don't see any mounting difference between 3297 and 3283 (see picture below).

Furthermore, what's the difference between the "R" and "E" letters for 3293 & 3305. Don't they both mean "Ohm" ? Is there any reason for Marantz to use both notations in this diagram or is it just an inconsistency?

Marantz PM-68 Main circuit left amp +56V
Marantz PM-68 Main circuit photography
Marantz PM-68 disassembled

Best Answer

I came across resistors with odd symbols (see page 18). They are trapped between two parallel lines (for example, 3297).

crop from schematic supplied in the question, showing the unknown resistor symbol

(Crop from the original schematic, showing the unknown resistor symbol.)

Answer: That is one of the (many) symbols used for a fusible resistor. Here is an extract from page 177 in the book: Electronics for Service Engineers by Joe Cieszynski and David Fox (Google Books link to page 177) showing that symbol, which I've marked in red below:

Figure 11.4 from "Electronics for Service Engineers" by Joe Cieszynski and David Fox

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