@onlyanalog The 66 pre-amp was released alongside the MkII amplifiers I believe. There was also a 6677 pre-amp that was dual mono (it was just two 66 pre-amps stacked on top of each other with one face plate.
I read somewhere that the pre-amp pairs well with the Bedini amps because they both invert polarity, but I can't find where I read that right now.
Here's the specs for the 66 pre-amp from the manual:
RMS Power (@ 1kHz): 11.5 Volts into 600 ohms
Freq Response @ Full Power: 5Hz to 35kHz
Freq Response @ 1 Volt, 600 ohms: 5Hz to 100kHz
Phono Overload: 1Khz, 500mV
Phono amp output Voltage: .5 Volt input for 6.25 volt output
Slew rate in Aux: 100 V/us at 11.5 Volts output
T.M.I. - .22 20 Hz to 20 kHz
T.H.D. - .015% 20 Hz to 20kHz
IM Mixed Frequency 4:1 ratio - .015% 20 Hz to 20kHz