--- In TekScopes@..., David Wise wrote:
Better cobble up some temporary loads from standard resistors, until you're sure the surrounding circuit won't kill them. They'll work at moderate sweep speeds so you can test and debug.
Dave Wise
Dave,
Thank you for the excellent suggestion.
I figured I can build a network from four 2 Watt carbon comp. resistors, physically arranged in a Z configuration. It looks like it will even fit in the existing space with some gap between each resistor. This should allow me to get nearly the full 8 watt possible dissipation. Since the horizontal BW is only 240 kHz, I don't think parasitic capacitance will be much of an issue, although the impedances are high so it is not insignificant.
I did some calculations that show the peak power dissipated in normal sweep operation or static movement of the beam when not triggered is within the 5 W rating of the existing resistors, but not by a large margin (4.67W for the 25 kOhm one.) However, the amplifier will be driven beyond this range when in the 5X sweep magnifier is used, or if a high amplitude external horizontal signal is applied to the input. There is no provision to clamp the tubes at a safe plate voltage. In addition to the potential to destroy the plate resistors, this condition will exceed the maximum plate current specification.
- Steve
