Re: Frequency counters
The issue of "light touch" pick-off buffers is both interesting and tricky- I've tried a few lash-ups, but even tiny capacitance can make a difference at the HF ends where there is a wide frequency span and reliance on minimum strays.
This may be heretical to some, but the next rainy-day step is to try one of the cheaply and widely available tiny wire-ended battery pentodes as fractional-pF ("gimmick", etc) pick-off, low anode load initial buffer into an otherwise semiconductor slight gain/low-Z output stage. Even a cathode-follower EC90 or low anode load EF95 would give space, power, heat and stray capacitance issues in many oscillator boxes.
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