Crackle just like cathode/heater leakage in one of the valves, but
active test as perfectly good isolation .
This crackle was present on first receipt testing but now with
close-handling not the slightest trace - typical symptom of PbFitis ,
also can be similar "bacon and eggs" crackle .
Any known problem area? hopefully not with the DSP chippery.
( just dealing with a Hartke HA3500 with pbfitis , but as 2006 a bit
more excusable)