I used this to use both channels of a Fender Tone Master Deluxe Reverb. If you normally jump it or use a normal ABY, there is a phasing issue. The ISO switch
Tone Master® Deluxe Reverb® | Guitar Amplifiers
Review: Fender Tone Master Deluxe Reverb and Twin Reverb
Deluxe Reverb - Both channels together for heavenly tone! | Gretsch-Talk Forum