Jim Lesurf wrote:

Eeyore wrote:
Jim Lesurf wrote:

More to the point, the original IV limiting using on the 405 was
particularly severe for reactive loads - rather common for
loudspeakers!

That's a very interesting subject in its own right.

Back then, designers tended to be 'over-protective' of their output
devices. No doubt influenced by the fragility of early parts.

A few decades ago the power devices were rather prone to secondary
breakdown, and had quite modest IV handling.

Things have moved on a bit. I tend no to look mainly at average
dissipation as opposed to instanteous V/I limiting now.

Can't say I've seen many failures.

Opps, giving my secrets away here.

Not sure what 'secrets' remain. Even by about 1980 I had no problem
designing a 200+ Wpc amp that used no IV SOA limiting for protection. Just
needed power line fuses. Just a matter of designing for the task. I'd
always thought that IV limiters were a dubious idea. The original 405 just
confirmed that for me. Given how much device technology has moved on, I'd
expect it to be a trivial to make a safe amp with no explicit SOA
protection these days if the designer knows what to do.

Might need rather more output devices than the bean counters would be happy
with though.

Graham