Indeed Pete. . . There are two possibilities when a grid resistor blows. To find out which one it was remove the tubes and measure the anode to grid leakage current at 2x the rated anode potential with a breakdown voltage tester (BVT). If the measured current is less than 10uA, the tube did not flash over. Instead, the burst in grid-I that blew the resistor was caused by an unloaded condition - for which there are also two possibilities. 1. the antenna became disconnected or 2. there was an intermittent burst of VHF energy that was blocked by the HF-tank -- which acts as a LPF. To discourage VHF parasitic oscillation, reduce the Q of the VHF suppressors It's also a good idea to incorporate extensive glitch protection in any amplifier.
Originally Posted by K1ZJH
• Rich, AG6K, [url]www.somis.org[/url] 805-386-3734