From Newsgroup: rec.audio.tubes

These old Br|+el & Kj|ar 2107 units are incredible pieces of analog engineering, but they definitely get finicky with age. If your frequency response or filter sweeps are tracking inconsistently, it's usually down to dried-out electrolytic capacitors in the power supply or dirty contacts on the range switches. Give the mechanical contacts a thorough clean with some DeoxIT before adjusting any internal pots.
If you are trying to verify its filter accuracy and don't have a second calibrated hardware analyzer handy, it can be helpful to cross-reference your sweep measurements digitally. You can look at a modern <ahref="https://noisemeter.co/sound-spectrum-analyzer/">sound spectrum analyzer</a> software setup just to map out the audio spectrum and check if the B&K hardware is actually centering on the correct harmonic bands.
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For full context, visit https://www.electrondepot.com/repair/bruel-kjaer-2107-frequency-analyzer-111868-.htm

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