Pedals that stack with the Fender FSR Blues Junior IV (Black, Greenback Speaker)

Tone City Model B Distortion TC-T31

Tone City Model B Distortion TC-T31 stacks high gain on top of the mid-forward already here

Zvex 59 Sound

Zvex 59 Sound leans toward edge of breakup, and that's a real, usable character to pair with

Catalinbread Formula 5F6

Catalinbread Formula 5F6's own harmonically rich character is the real reason this is worth trying

Catalinbread Valcoder '70s Collection

Catalinbread Valcoder '70s Collection's gritty voice goes after Fender FSR Blues Junior IV (Black, Greenback Speaker) in the signal chain — it's not there to compete with Fender FSR Blues Junior IV (Black, Greenback Speaker)'s own mid-forward character

Origin Effects SlideRIG Compact Deluxe

Origin Effects SlideRIG Compact Deluxe's own compressed character is the real reason this is worth trying

EarthQuaker Devices Afterneath

EarthQuaker Devices Afterneath's ambient voice goes in Fender FSR Blues Junior IV (Black, Greenback Speaker)'s effects loop — it's not there to compete with Fender FSR Blues Junior IV (Black, Greenback Speaker)'s own mid-forward character — goes in the amp's FX loop (or last, into a clean amp)

Boss DD-7 Digital Delay

Put Boss DD-7 Digital Delay in Fender FSR Blues Junior IV (Black, Greenback Speaker)'s effects loop, clear of Fender FSR Blues Junior IV (Black, Greenback Speaker)'s own gain stage — goes in the amp's FX loop (or last, into a clean amp)