David McGown wrote:
Transformer coupling is generally regarded as better of the two, since it is not subject to blockage when entering Class A2 operation (i.e. when the driven signal at the grid swings positive with respect to the cathode and the grid starts pulling current). Therefore, you have more headroom with a transformer. On a full bandwidth amplifier, the quality of the interstage transformer is critical, and you want an interstage transformer that has enough inductance to support the driver tube at very low frequencies, and very good high frequency performance. This makes for a challenging design. It also needs to be carefully selected to match the driver tube plate impedance and operating current. However, you can use an interstage transformer to deliver more current (using a step down ratio) for output tubes needing more control, or increased voltage (step-up ratio) when using a driver that does not have enough voltage swing. Generally, it is preferred to either use a 1:1 or a step-down ratio for maximum bandwidth and driver current.
David
Very Informative
It makes the case for separately driving the low bass frequencies and hi-passing (at line stage) rest of the frequencies, doesnt it?
I am going to try both PowerDrive and Transformer coupling topologies. PowerDrive seems to be the simplest and cheapest as TubeLab is selling the PCBs and standard products from DigiKey/Mouser are used.