Biasing info
Normally set EL34s to around 35-45mA. This will sound OK and will
give the tubes the maximum life. You can also bias up to about 50mA but then tube
life starts to go down.
For the KT88/KT100 the bias should be around 45-60mA but shouldn't go over 60mA.
Look out for red spots as a warning that the bias is too high.
On the Ella the bias is measured as a voltage. Since there is a 10ohm
resistor on the cathode circuit the current can be calculated using the formula I=V/R.
For example:
I = 0.42V / 10R = 0.042A = 42mA
(Note that 0.42V is the same as 420mV)
Valve pins
| |
Valve type |
| Pin |
6922 |
6SN7 |
EL34/KT88 |
| 1 |
T2: Plate |
T2: Grid |
Grid 3 (Suppressor) |
| 2 |
T2: Grid |
T2: Plate |
Heater |
| 3 |
T2: Cathode |
T2: Cathode |
Plate |
| 4 |
Heater |
T1: Grid |
Grid 2 (Screen) |
| 5 |
Heater |
T1: Plate |
Grid 1 |
| 6 |
T1: Plate |
T1: Cathode |
- |
| 7 |
T1: Grid |
Heater |
Heater |
| 8 |
T1: Cathode |
Heater |
Cathode |
| 9 |
Internal shield |
|
|
