The "catch" when bridging vacuum tube amplifiers is that you need to go down to the next lower output transformer matching tap for correct impedance matching to the speaker. A 16 ohm speaker looks like an 8 ohm load to a bridged amp, an 8 ohm speaker a 4 ohm load and so on.
With solid state amplifiers with very low output impedances there is no multiple output taps, one source drives anything within the current limits of the amplifier.
With vacuum tube amplifiers you need to match impedances as mentioned above. And each lower output tap puts out a higher output current but less output voltage than the higher impedance taps. So when you bridge vacuum tube amps, you do not double the output voltage and thus quadruple the bridged single power rating, you only double the power rating. V remains the same, but R is cut in half and V squared over R only yields X2 power instead of X4.
Got it?
However, X2 power and X2 current into that load is still provides a very healthy bridged amp into difficult loads.
Regards,
Frank (just back from being snowed in, very happily, in the Wisconsin North Woods for three days watching the deer play in the yard).
