• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube 'test' interpretation

I was getting some weird results swapping around driver tubes in an amplifier, so I wanted to get an idea of the state they were in.
I don't have a tube tester, so I just put them in another amplifier with a similar topology.
The type in question is the EF184.
B+ = 295V
Vg2 = 145V
Ra = 10K
Rk = 105 Ohm

I measured the anode voltage:

1. 121V
2. 195V
3. 198V
4. 152V
5. 196V
6. 189V
7. 191V
8. 198V
9. 176V
10. 198V

I don't have much experience with such measurements, how do I interpret these results? Most are around 190-200V, the ones with a significantly lower voltages seem 'not so good', and the 121V seems really questionable.
Would you agree, or am I missing something?

Thanks in advance.
Joined 2004
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If you see the EF184 datasheet, and interpolate from -the lowest- Vg2=160V curve to 145V, on this gate the current would be a little more than 4mA.
The estimated anode current about 10.. rather 11mA.
Via the cathode resistor (105R) flow these currents, about 15mA, so bias voltage a little bit more, than 1.5V.
The estimated anode current flow through anode resistor (10k), so there the voltage drop 110V.


Weaker tubes produces higher voltage here, stronger creates lower.
If you select tubes 185V +/- 5% (about +/- 10V), its behaviour would be similar.
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