Vibro King "style" clone w/4x6L6 : Hiss noise

[Jazz-O-Sonor]

Hi,

A friend of mine made a Vibro King "style" clone w/4x6L6
This amp sounds fantastic ; but he needs help on a bug:
1)When the "FAT" switch is disconnected there is a nasty
Hiss noise ; so pls can anyone help to figure out how to fix
this? thx

(also; there is always a low volume hum noise but this could
be probably caused by the unmatched 6L6 )

thank you in advance ,John

ps: I included few pictures of this beautiful build

[Jazz-O-Sonor]

picture#2

picture#2

[Jazz-O-Sonor]

picture#3

picture#3

[Jazz-O-Sonor]

picture#4

picture#4