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The example fails minimum inductance requirements

"A recent, specific example is increasing the inductance for a 300B amp from 24 henries to 40 henries, both with a 3000 ohm output transformer. The bass improvement is clearly audible."

Paul, the rule of thumb I use regarding the shunt reactance across an AC circuit is that it should be no less than 5X the operating impedance at the lowest frequency of operation. 10X the operating impedance is better. In the example you cited, with an operating impedance of 3K ohms, XL should ideally be about 30K, although 15K is probably acceptable. The 40H choke in your example fails to meet this requirement, as it presents only about 5K. Making matters worse, it's in parallel with the inductance of the OPT, so the final value is likely to be considerably less. The difficulty in maintaining minimum required inductance is one of many reasons I've never been tempted to build parafeed amplifiers.



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