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Post by roly on Jun 9, 2021 23:07:32 GMT -5
A reverb driver tube in an AB763 amp is like a bridged power amp. ?
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pdf64
Wholenote
Posts: 553
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Post by pdf64 on Jun 10, 2021 3:49:57 GMT -5
No, it’s a single ended power amp, same simple mode of operation as the 6V6 in a typical Champ. The 2 triode sections in the 12AT7 are wired in parallel. That effectively creates a valve that has twice the max anode dissipation, twice the gm, and half anode resistance, compared to a single section. So it’s a simple method of getting more muscle from the driver, pushing twice the power into the reverb tank. Of course the designer could just as easily decided to get similar, perhaps better, results by using a ‘proper’ pentode output valve such as a EL90 / 6AQ5, but for whatever reason, the paralleled 12AT7 was chosen and it does the job just fine.
So how’s that different to a bridged amp? A bridged amp uses 2 power amps working in push pull, ie a balanced system with each side handling opposing polarity signals. That doubles the signal voltage across the load (speaker cab) and twice the voltage equates to 4 times the power. But both lines to the cab are ‘live’, carry signal, neither are ground / neutral. So 1/4” jack connectors aren’t really suitable.
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Post by roly on Jun 10, 2021 14:10:13 GMT -5
Thanks very much Peter.
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