The David project was an entertaining exercise in how much stuff can be crammed into a small box... The donor chassis' were a pair of Motorola SE 6BQ5 stereo amps. One of the amps came from a Motorola mini console, the other amp came from an AMC mini console.

In each amp the power supply was changed to a full wave bridge with choke input to get the supply voltage up for the active loading. One of the 6BQ5's was retained as the output stage CCS. One of the original SE output transformers was used as the power supply choke. Managed to cram 3 CCS boards into the chassis... The output transformer is a 70 volt line matching transformer, the cheap one that Radio Shack used to sell.

The David uses a 6AN8 triode/pentode as the input tube. The triode section is used as the input stage while the pentode section is used as the CCS for the input stage. The input stage is RC coupled to the EL84 CCS loaded 12B4 triode output stage.  The driver stage of the David has a CCS fed shunt regulated power supply.

The pair of David monoblocks are used as my lab amps and see almost daily use. They put out 1 clean watt that is very transparent and has great bass. At full power of 1 watt the frequency response is 30 to 22K, at low power levels the response is better going from ~20 to 30K.

One of my friends uses a pair of David's to power his Klipsh LaScala's. More power than he needs in a small room ;-}

The schematic...

Front view...

Rear view...

Inside...

Close up of the input and output stage CCS's...

Close up of the shunt reg...

Below is a very crude had drawn schematic of one channel of the original Motorola SE 6BQ5 amplifier. There should be a cap to ground on the screen supply. These little stereo amps sound pretty good after you remove the frequency shaping networks in the feedback network. Remove the small .047uf cathode bypass cap on the input stage. Also remove the 33K||.1uf network in the feedback path by directly connecting the 8.2K feedback resistor to the cathode of the input tube. The 150K resistor to the screen supply injects power supply noise into the cathode trying to improve the power supply rejection ratio of the input stage.