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help ID tube with no marks


2012-02-05 1:15 am
Please need help to identify a tube with no marks .

Came in a custom Single ended stereo 300b amplifier from Japan that also use ECC82 tubes. It is a 9 pin tube and use 6.3v filament, overall high close to 66mm, 51mm without pis and exhaust tip, 20mm wide. No marks, letters or numbers on glass. The tube on amplifier use only pins 1,2,9 and 4&5 filaments. Wiring details wrote on photo.




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Its a 6S4A

The tube in the picture looks like a 6S4A, I have never seen that type of plate structure in a 12A4 or a 12B4.
The 12a4 and 12B4 have an open plate design which is open and you can see the grid and cathode from two directions.
Many tubes are mislabled, especially tubes with "International" as brand.

Been working with tubes 30+ years and still learning.

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