--- 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