what purpose do the diodes on the powertube give?

[wsaraceni]

in the francesca pics/schematic there are 3 diodes connecting to ground on each power tube. what purpose do they serve?

thanks in advance

bill

[doctord02]

Bill these are fly-back voltage spike protectors. It was a safety mod KF used to do on Marshalls as well - any amp that was driven hard to keep a shorted tube from taking out the OT. In the download section you can find Ken's description of this mod in a file I uploaded to the site called "The Trainwreck Pages" that was printed by Angela Instruments in their mailorder catalog.

[wsaraceni]

thanks for the reply. i'll check those pages out as well.