HARTKE Systems Model 3500

hartke 3500 bench test

Bench Testing the 3500 Amplifier Module

The photo above shows the 3500 module powered by my bench supply.

The Fluke on the right displays the rail voltage at 87.2V

DC Offset was adjusted to 7.6mV.

Oscilloscope square wave display is 10kHz, measured at output of amplifier.

The rebuilt with 2SC5200/2SA1943 transistors is shown to be stable. No oscillations observed.

Thermal control is working properly. No thermal runaway on power transistors.


On inspecting the pcb, I found that the 0V tracks of the voltage stage and current stage are not connected. This is not a fault in manufacturing.

Some designers prefer to have high current grounds separated from voltage grounds to lessen the possibility of contamination.

Eventually, all common grounds will be connected when the Hartke is fully assembled.

On the bench, the amplifier module will not work unless the grounding is resolved.

The yellow wire under the pcb does exactly that. It connects the voltage stage 0V with the current section 0V.

Now, the module is fully functional.

hartke 3500 pcb mods

60 Downes Street | Calais | ME 04619 | USA