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Bootstrapping would certainly boost the shunt resistance at very low frequencies, but there's an inherent grid-cathode conductance that grows quadratically with increasing frequency to spoil the fun fairly soon. At even low "rf" that conductance will greatly exceed 1/100megohms, so I am pessimistic that bootstrapping will buy much at frequencies of relevance for most uses. I'm used to seeing unbootstrapped numbers like 10s of kilohms at 10s of MHz for tubes that are probably not grossly different from the 535. So, I would guess that the law of diminishing returns kicks in pretty hard a bit above the audio band. A bit beyond that and bootstrapping is not going to help materially. And that assumes no additional conductance arising from ordinary leakage due to grunge, humid ambient, etc.
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It's certainly worth a try, though, since the mod is quite easy (and easy to reverse). Cheers Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/23/2022 14:02, John Kolb wrote:
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