Them dang LM338s

[Shredly]

Yes, to get current limit you put a sense resistor in the emitter lead and use it to turn on another transistor which will pull down the power transistor base.

Hmmm, well actually I was thinking of limiting the combination by putting it between the output from the input filter and decoupling caps, and the input to both the regulator and the transistor. This is how both National and NEC recommend doing it in their appnotes.

But you only need 0.65V to turn on the transistor so 0.22ohm will give you a 3A limit thru the transistor + whatever the regulator will give.

I want the same limit as the LM338 has on the other rail, so for 5A at 0.65V that would be 0.13 ohms (the closest 5% value), which would give a power of 3.25W- 5W to be safe. They're $1 to $3 depending on precisely what you want- you can get 1% for about $2.

Also worth noting this is well within the current handling capabilities of the 2N3055, at 15A or so; at 4A, with 7V across it, it will dissipate 28W, so you'll need a heatsink for sure, since the TO-3 case only dissipates a few watts on its own. Get the ST part, BTW- the original part didn't handle this kind of current.

Personally I would not bother with that arrangement I would use a fuse.

I guess that's a matter of the use you intend to put it to- and I wouldn't use a standard or fast-acting fuse, I'd go with a slo-blo. But then again, since my amplifier is intended to be used in performances, I'd rather not be blowin fuses on stage.