11-11-2016, 12:30 AM
Hours of fun indeed. I did try feeding a high level 45mhz modulated signal into the anode of the penultimate TRF amplifier stage, the highest demodulated waveform across the detector load was only 6volts P - P. The final TRF stage employs an MSP41 pentode. This valve was chosen to handle the higher amplitude signal suppied to it's grid. Whereas the cathode bias resistor of all the other MSP4 pentode amplifier stages is 150ohms it is 500 ohms for the MSP41 which indicated the valve must have a greater grid base characteristic.
The CRT in the 702 is quite good but the picture has a milky appearance because of the low video drive.
AC coupling between the detector and CRT grid results in the loss of the DC component.
Dependant of picture content the black level wanders about a mean value.
Geordie McBoyne.
The CRT in the 702 is quite good but the picture has a milky appearance because of the low video drive.
AC coupling between the detector and CRT grid results in the loss of the DC component.
Dependant of picture content the black level wanders about a mean value.
Geordie McBoyne.
