Here's Valve Wizard's take on the PT2399 delay. It's very similar to most PT2399 delays out there, with a dual op-amp providing input and output buffering. This was designed with the tails function and it uses Valve Wizard's usual J112 switching. Here's his original schematic and explanation of the circuit. You can also use a DPDT footswitch for bypassing, using one side to turn the delay on/off and the other for LED indication. I've included 2 extra pads on the PCB layout for this function. If going this route, don't populate the J112 along with the 1N4148 diode, 1k and 4.7k resistors, and 10µ capacitor round the J112.
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