23-09-2019, 09:16 PM
It's a cute little valve, easy on the heater power as you say.
The common cathode makes it awkward to use sometimes though. In your circuit you have made things easy for yourself, with the external pentode bias, and contact-potential bias for the triode, and taking the cathode directly to circuit 0V.
There is a fair bit of gain present, depending how much of a rats nest your wiring is! Long wiring on the pentode anode is bad news as is unscreened wiring on the triode grid. Coupling between the two will be positive feedback so it is easy to make it hoot.
It is good for a watt of audio, which with a decent speaker is highly useable!
Mullard developed a circuit using two in push-pull for 3W. And they had another, rather quirky circuit which uses the ECL80 pentode as a phase inverter (working at very low current), and the triode as an oscillator... the grid-leak bias developed in the triode was used to bias two push-pull PL81 output valves without wasting voltage in cathode resistors. But that's all going off-topic!
The common cathode makes it awkward to use sometimes though. In your circuit you have made things easy for yourself, with the external pentode bias, and contact-potential bias for the triode, and taking the cathode directly to circuit 0V.
There is a fair bit of gain present, depending how much of a rats nest your wiring is! Long wiring on the pentode anode is bad news as is unscreened wiring on the triode grid. Coupling between the two will be positive feedback so it is easy to make it hoot.
It is good for a watt of audio, which with a decent speaker is highly useable!
Mullard developed a circuit using two in push-pull for 3W. And they had another, rather quirky circuit which uses the ECL80 pentode as a phase inverter (working at very low current), and the triode as an oscillator... the grid-leak bias developed in the triode was used to bias two push-pull PL81 output valves without wasting voltage in cathode resistors. But that's all going off-topic!
