Piezo preamp for string bass

[Quayhog]

I have a lot of PA amps, mostly Grommes, Dukane and Altec that I can modify one for use with a piezo equipped string bass.  Has anyone had any success modifying a tube circuit for this use?  Is there anyway to transformer couple the input?  I have some UTC and Halldorson interstage transformers which would give a higher loading to the pickup.  Would they work for that purpose? KK pickups require a 1M-5.6M input impedance.  How much of the input load needs to be on the primary side? Can it be adjusted with a resistor?

Jonathan Horne