2. amps-preamps
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Cary SLI-80 Tube amp suddenly blowing fuses

Very strange problem. Everything works and plays fine, however, the past 2 days I have blown the ac fuse (3 amp slow blow 250v) twice now! The bizarre thing is that it only blows when the Cary is in a resting state ~ for an hour or two. When I am playing music, everything is fine! Strange. Could it be random power line surges? Do you think it is a deeper problem within the 6 month old Cary? Should I swap out the power cord?

Thanks,

Jason
jfiluk

Showing 3 responses by john_tracy

john_tracy
343 posts
 
Could be a bad rectifier tube. If they short it will pop the AC fuse. Happened to me with a NOS RCA GTB. Tube tested OK on tester, but the higher voltages in amp would cause it to short.
john_tracy
343 posts
 
Probably won't if you don't stick a "bigger" fuse in it.
john_tracy
343 posts
 
When you bias an amp you are setting the idle current in the output tubes. This is measured in mA. I think the confusion comes fronm the fact that different manufacturers use different methods for measuring this current. The Cary measures this directly with an ammeter. Others will insert a small value resistor (say 10 ohms) in series with the output tube and one determines the idle current by measuring the voltage drop across the resistor. For example, if you measure a voltage of 0.65mV across a 10 ohm resistor, then by Ohm's Law (V=I*R) the current is 65mA.
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