Guys:
The high transient SWR only lasts for a second or two.? Assuming these transients cause high power dissipation in a BS170.? The chip inside the plastic transistor case may rapidly heat and die meanwhile the thermal capacity of the case may slow its temperature rise.?
Extra external heat sinking for this possible failure mode may not help even if it helps for continuous high power operation.
Unfortunately: 1) We cannot do a transient thermal model because there appears to be no useful published thermal data on the BS170. - This use of the BS170 is not what it was intended for.
2) Secondly detail Spice model for the PA Stage and LPF would need to be developed to determine the power transient.?
So my recommendation is to be careful in the use of auto tuners.?
I believe Hans will incorporate some high SWR protection in future firmware but it will need to be reasonably fast to protect against transients.? I hope Hans will incorporate a Tune Mode at ~1/3 power by commanding Q507 to lower the TX voltage to ~6.5V
