Cary SLI-80 Tube amp suddenly blowing fuses

John, you're definitely more on the ball than I am when it comes to this stuff. I've only owned VTL amps, and the Cary. With the VTL amps, one measures the voltage vs. the amperage. Of course, using your formula, it looks like one is actually indirectly measuring amperage?

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.

The manual I received with the amp state that one uses mA to bias with. I have had no trouble biasing the amp. It's actually much easier than adjusting bias on the VTL amps I've owned.

Hedge- Give Cary a call. They're great guys and will talk you through all the ins and outs od biasing, etc.

Have fun!

Doesn't Cary recommend measuring mA, not mV, when adjusting bias?

Probably won't if you don't stick a "bigger" fuse in it.

I wonder if this would damage any internal components of the amp?

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.

I had blowned the ac fuse on my Jolida amp once. I checked the bias setting and there's no problem, think it's more a bad tube. I have replaced the tube and it's doing well now.

Jason-

In talking with Cary regarding biasing that amp, they gave me some advice that I found was very useful.

If your system leans toward the bright side of things, bias higher than 75. I experimented and found mine sounds best biased at about 90 to 92. You can bias that unit at up to 105 or so and never worry. 175 however, is definitely out of the park!

You may want to experiment sometime.

Enjoy that lovely and incredible amp. I love mine!

Ok I just rechecked the BIAS. I had it set to 175mV instead of 75mV. Heh heh. Hope I didnt wear down the new tubes too much.

Could that have been the problem? Keep in mind it was the AC fuse that blew, not the tube fuse.

Thanks,

Jason

Jason:

Which power tubes are you using? The fuse blew on my SLI-80 once due to a bad tube. What's the bias value? BTW: There's no resting state for a tube amp. Once warmed up, mine draws a steady 215 watts whether playing or idling. It's called a resistive load.

Good luck,
Jay