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RE: Bias on Manley Snappers

Posted by Jim McShane on February 16, 2017 at 13:47:59:
You got 6CA7s that are too hot (hot = higher current under a given set of operating conditions). Your amp does not have sufficient bias adjustment range to bring the current down to spec. There is nothing wrong with the tubes per se - they are just a misfit for the amp.

You need a set of 6CA7s that are mid range to cool biasing (cool = lower current under a given set of operating conditions). Then you'll be able to adjust the bias to the specified range.

Yes it IS a problem that the 2 tubes are at .416! That is roughly 30% over the spec for the amp.

And finally the .416 is NOT current (ma.) It is VOLTAGE!! It's the voltage developed across a 10 Ohm resistor in the circuit between the tube cathode and ground by the current flowing through the tube and on through the resistor. Using Ohm's Law you can compute the current. The current equals the voltage (.416 volts) divided by the resistance (10 Ohms) which equals .0416 or 41.6 milliamps (abbreviated ma.)

If you own a tube amp it behooves you to learn about bias and biasing so you don't get confused by it.

BTW - what brand 6CA7s are you using?