New amp is here!!

[maiden666]

Hi got rid of the mode four and 1936 cab as it was too big for our sittin room and got a used marshall tsl601 combo.Its great but when i switch the stanbye on i get a whoosin crackle sound for a few seconds then it dissapers strange?,the power valves look fine glowing at top and bottom and that blue haze u get.Any ideas regards dave