9b260a7e   
   From: pds@ktb.net   
      
   Tabby  wrote:   
   > On May 31, 6:59?am, "Phil Allison"  wrote:   
   >> "Paul D. Spiegel"   
   >>   
   >>   
   >>   
   >> > What do RATS use as a "rule of thumb" to select a fuse for a power amp?   
   >> > In the past I've doubled the idle current, but honestly, that was just a   
   >> > guess. ?How do you choose?   
   >>   
   >> ** Kinda depends a lot a WHERE ?in the circuit the fuse is going to go.   
   >   
   > It also depends in this case on the supply voltage. Eg for 240v, for a   
   > general purpose audio amp, 2A fuses tend not to last so well, 3A do.   
   > On 110v you're likely not looking at a slightly fragile low current   
   > value like 2A.   
   >   
   >> HT line before or after filter caps ?   
   >   
   > which also depends on the resistance/impedance in teh circuit, since   
   > that determines the power up surge. And reservoir cap size determines   
   > its duration - eg a prewar amp with 4uF main resevoir cap will see way   
   > less i squared r at startup than a later amp with maybe 100uF. Also   
   > the type of rectifier: a valve rec will pretty much eliminate power up   
   > surge, but silicon diodes wont.   
      
   Interesting point, NT.  In this case the line voltage is 120 (I forgot   
   to mention in my previous reply).  The PS for this amp is a tube   
   rectifier with a choke input, so start-up current is minimized, but it   
   is something I should consider when using SS diodes and a large filter   
   cap first.   
      
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