V4B Ampeg, trying to diagnose over the net for a friend

[g1]

It should have been, but there must have been something bigger in there which is why the internal 10A blew. That's what 52Bill mentioned.
Had there been no internal 'back-up' fuse, much more serious damage could have occurred, depending on what was really installed in the external fuse holder.

[olddawg]

It should have been, but there must have been something bigger in there which is why the internal 10A blew. That's what 52Bill mentioned.
Had there been no internal 'back-up' fuse, much more serious damage could have occurred, depending on what was really installed in the external fuse holder.

My favorite was always 1/4" aluminum dowel cut to fuse length!

[Enzo]

I found a hunk of 1/4" bolt in a fuse clip once. But they at least used gold plated thread stock.

[g1]

And the good old classic:

[reddart]

Looks like we may have found a culprit...one of the diode strings to the plates appears to be conductive. That would definitely do it.

[52 Bill]

Looks like we may have found a culprit...one of the diode strings to the plates appears to be conductive. That would definitely do it.

And shorted flyback diodes could be caused by a lack of output load or dirty impedance switch as Leo_Gnardo suggested.