I had a similar experience to Mike this afternoon. While running the 72kHz
transmission I noticed that the support insulator support cord near the
loading coil had parted and the antenna was held only by the lead from the
coil to the insulator. I found that the nylon cord had burned through. I
switched off the transmitter and replace the coil with a length of copper
wire to support the insulator.
I use  insulators kindly supplied by Dick, PA0SE. These are serious
insulators some 150mm long (6 inches in old money) made of glazed ceramic.
When I fired up the transmitter again there was a spluttering noise from the
insulator with slight variations in antenna current. There were small
dragons of sparks up to 40mm long snaking up and down the surface of the
insulator, accompanied with puffs of steam (it was raining at the time).
I think the problem is caused by salt, although it should have washed off -
it had been raining all day. Since the storm the windows in the house are
all coated with a salt  layer.
The wireless ops chore of cleaning the insulators, described in the
Admiralty Handbook of Wireless Telegraphy, was necessary to remove dried
salt. Obviously the same routine needs to be applied here.
Many thanks for those who sent reports on the 72kHz transmission. I was
using the three modules and was running just over 1kW to the antenna.

Regards,
Peter, G3LDO

e-mail <[email protected]>

Web <http://web.ukonline.co.uk/g3ldo>