# Tube 'test' interpretation

#### Miniwatt

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?

#### euro21

Paid Member
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.

295-110V=185V

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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