50CA10 triode vacuum tube - Rarer and rarer...

Unobtanium audio output tubes - The NEC 50CA10 Triode vacuum tube.

Luxman had a thing for "special" vacuum tubes back on the 1970s. The 6RA8 triode (also used in the Sansui BA-202) and the big, robust 50CA10 used exclusively by Luxman. Both were one-off units made by NEC (Nippon Electric Company) in Japan and no modern or vintage equivalent exists. They are no longer in production since the late 1970s. The 50CA10 was (is) also a triode tube capable of a max of 30 watts. Fairly robust and really excellent as an output tube. Shuguang Tube Factory in China made a copy for a time, but they were of questionable reliability and not much is known about them. They are no longer in production from Shuguang. Any 50CA10 is most likely available in Japan, used or NOS, for pretty steep prices. Amps that used them were the excellent SQ-38F, FD, FD MkII and some of the MQ series. They are long-lasting and sound excellent...as long as they are in a well-restored and balanced amp.

Here’s a cross-reference chart comparing the NEC 50CA10 to similar vertical oscillator/output triode-pentode tubes, focusing on heater specs, electrical functions, and general compatibility:

📊 Vertical Oscillator/Output Triode-Pentode Tube Cross-Reference Chart

Tube Type	Heater Voltage / Current	Triode Function	Pentode Function	Notes
50CA10 (NEC)	50V / 0.45A	Vertical oscillator	Vertical output	Japan-only tube, 12-pin base
10CA10 (NEC)	10V / 0.6A	Vertical oscillator	Vertical output	Same tube as 50CA10 with different heater
6CA10 (NEC)	6.3v / 0.9A	Vertical oscillator	Vertical output	Same tube as 50CA10 with different heater
17GT3 (GE, RCA)	17V / 0.45A	Vertical oscillator	Vertical output	U.S. TV use, similar functions
21GV8	21V / 0.6A	Vertical oscillator	Vertical output	Functionally similar, different heater
10GV8	10V / 0.6A	Vertical oscillator	Vertical output	Japan/US tube, lower heater voltage
PCL85 (Europe)	13.3V / 0.3A	Vertical oscillator	Vertical output	Very common in European TVs
PCL805 (Europe)	13.3V / 0.3A	Vertical oscillator	Vertical output	Improved version of PCL85
6GV8 / ECL85	6.3V / 0.76A	Vertical oscillator	Vertical output	6V heater version of PCL85

🔍 Notes:

• 50CA10 and 6CA10 / 10CA10 are electrically identical except for the heater—50V vs 6.3V / 10V.

• PCL85/PCL805 are close functional matches but use different heater specs (European 300mA series string).

• 17GT3 and 21GV8 are the closest in American TV usage.

• 10GV8 is sometimes listed as a sub for 10CA10 and functionally very similar to 50CA10 (except heater voltage again).

• So while the electrical function of the 50CA10 aligns with tubes like the 17GT3, 10GV8, or PCL85, the mechanical base (12-pin) and heater voltage make it not physically interchangeable with those 9-pin types.

  There is no Western direct counterpart with the same electrical + mechanical combination — the 50CA10 is distinctly Japanese, purpose-built for their unique power and design constraints.