help ID tube with no marks

[kkstereo]

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.

PHOTOS ATTACHED

THANKS

 

[smoking-amp]

12A4, 12B4

check for htr tap on pin3
Check heater current.

 

[Tubelab_com]

12B4 was my first thought, but a careful look at the picture shows no tap on that spiral wound heater. It's probably a Japanese made vertical output tube with similar characteristics.

I bet a 12B4 or 6S4 could be made to work. There is a similar Russian tube but I don't remember the number, 6S19P or 6P19S maybe.

 

[kkstereo]

current heater is 300mA, pin 3 just mica support

 

[kkstereo]

well,filaments are wired as parallel with the ec82cc so I assuming is 300mA

 

[kkstereo]

size compared to ecc82/12AU7

 

[kkstereo]

The 12B4 should be a winner , match data and pinout except the pin 3 , no heater tap on mine just mica support , but I think should work as good replacement for it. This amp using pins 1,2 9 only for that tube. The 6s4 do not match on pins. Thanks

 

[livingdeliberately]

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.

Cheers