SOME MODS TO THE VOLTIX 420-C5 OSCILLOSCOPE Actually many people would say that it is a crime to modify such equipment, but since it has been useless to me, and I needed another scope with vertical DC coupling capability, it was the time to make some renewing on this unit. Of course I will never damage the front panel, so, if I regret from doing these mods, I can reverse the modification without any pain....

    The "new" model will be called 420-C5/2 or "Mark II".....

    Here is the schematic of the new model.

    The calibration switch of the original 420-C5 was replaced by a Vertical MODE switch so now I can select between AC, DC, CAL or GND functions. The calibration generator was made with basis on the calibration unit of the IWATSU SS-6050, you can see SS-6050 manual on BAMA.

    The new vertical DC amplifier needed to be biased also by some negative power supply, and -75 is generated, and stabilized by B801, a 0A2. It is fed by T803, that used the 6.3V from the filament supply to get out around 95VAC. Also a 150V stabilized power supply was generated by The original 6V4 rectifier and the 1B3 HV rectifier were replaced by silicon diodes, just for convenience, and get proper room to the "new" tubes needed. (to be continued)...

   HOMETEST EQBRANDED GIGSLSG-532UPPHILIPS 661