Klausmobile Tube Tester Files

What a small tube tester can do with a power tube?

This is an odd octal beam tetrode - not used in any modern amps. It is small, about the size of 6SN7 / 6H8C, and the whole bottle, excluding the very top, is stained black. No wonder this tube was forgotten, as there's a direct replacement - 6P1P - in 9-pin mini package. However, even this one (in it's own time) was quickly replaced with 6P14P (=EL84). All these tubes operate at the same rated power/voltage/current/gain, yet EL84 yields more undistorted output and in fact became THE standard amplifier tube in old Soviet radios and TVs (SE output, of course).

Triode-connected curves - obviously, with 5W tester capacity only a small fragment of work area is exposed. What's worse (and it IS annoying) - opamp grid driver cannot go lower than 10V, and this tube needs -12V bias. Anyway, what's worth in this curve set?

We can compare the instrumental data with datasheet curve. As the superimposed charts show - the readings are fitting stock chart but the curves lay closer to Y-axis, showing somewhat higher transconductance.

Indeed, the datasheet quotes 4.1-4.6 mA/V at 45mA/250V while this tube has 5.2-5.5 at lower current.

Original datasheet - in addition to power audio application - also quotes terms of operation under extremely low plate voltage (26V at plate and G2, -1.5V at G1, 2.75 mA total current for 20mW output into 10k load). Which is quite close to this tube's measurements.

Triode connection

Legend: White curves: Ig<5uA Yellow: 5<Ig<20uA Red: 20<Ig<300uA. Measurements terminate at Ig>300uA

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