> The siganl source is from the follow device.
> 
> http://www.paintechnology.com/046.htm
> 
> TENS, Transcutaneous Electrical Neural Stimulation
> 
> My project is to increase the number of possible channel but at any
> one time the same number of channel support by the device

Rather than switch the signal, why not use amplifiers to copy it ? Then
switch signal paths on or off

Another option could be to use a PIC to examine the original signal
(2-150Hz, 60-250us pulse width). It could then drive a FET or FETs.
An 80V supply is not too difficult. Simple oscillator/inductor for example

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