sealed box tubes are audiophile crown jewels, hard to find sought after top sonic echelon, warm immersive hifidelity vintage
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the tube-era british supplied expertise + tooling via 'transfer of technology' resulted in several critical audiophile advantages:
...same anodes, micas, electrode geometry, glass envelope, spot welding, grid wire spacing and cathode processing chemistry!
carefully curated and screened direct japan import, popular 12au7 ecc82 plugin sub, ships w/ free postage
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if opened, give 100+ session hours w/ your specific amps voltage to fully cure and break-in
ships well packed worldwide ~ vintage hifidelity audio curation by cali acoustics