The idea of multiple leads is to minimize the inductance for UHF operation.
At UHF, every little fraction of a nH counts!
As a UHF amplifier it most likely was used in grounded grid connection (notice 3 grid pins).
The other clue is that 2 of the grid pins are between the 2 plate pins and the 2 cathode pins. That minimized the capacitance of the cathode to the plate, when the grid pins were grounded (acts like a shield).
I am guessing you will use this tube as an amplifier in common cathode mode (not grounded grid mode).
So . . .
You almost certainly will need a grid stopper resistor connected directly to one grid tab of the socket. That will slow it down at UHF (but not to audio)
Otherwise you may have an oscillator.
Connecting only one cathode pin, and connecting only one plate pin will also slow it down at UHF (but not to audio).
Depending on the placement of your wires, the circuit parts values, wire lengths, etc. you should be able to prevent oscillation.
Your mileage may vary.
Happy circuit building and listening.
At UHF, every little fraction of a nH counts!
As a UHF amplifier it most likely was used in grounded grid connection (notice 3 grid pins).
The other clue is that 2 of the grid pins are between the 2 plate pins and the 2 cathode pins. That minimized the capacitance of the cathode to the plate, when the grid pins were grounded (acts like a shield).
I am guessing you will use this tube as an amplifier in common cathode mode (not grounded grid mode).
So . . .
You almost certainly will need a grid stopper resistor connected directly to one grid tab of the socket. That will slow it down at UHF (but not to audio)
Otherwise you may have an oscillator.
Connecting only one cathode pin, and connecting only one plate pin will also slow it down at UHF (but not to audio).
Depending on the placement of your wires, the circuit parts values, wire lengths, etc. you should be able to prevent oscillation.
Your mileage may vary.
Happy circuit building and listening.
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Hello Goran!
The EC86 is a good little triode. But it likes to oscillate! This can spoil the sound. You can use an AM radio, to make sure it is not oscillating (tune to a weak station 150kHz-1500kHz and hold it near to the EC86) .
The oscillation happens because of the high gain and low capacitances of the EC86. You can help with some precautions:
- only use one grid pin, and one anode in.
- remove the socket contacts for the anode and grid positions you do not need. (The extra metal increases coupling, and makes oscillation more likely).
- use ferrite beads on the grid, and anode wires, very close to the socket.
- make the anode wire as short as possible.
- connect 1µF capacitor (stacked-film construction type) between the anode power supply + and -. Connect directly between the Anode load, and the cathode resistor. Make the wires short. (This reduces the effective distributed inductance of the anode circuit).
The EC86 is a good little triode. But it likes to oscillate! This can spoil the sound. You can use an AM radio, to make sure it is not oscillating (tune to a weak station 150kHz-1500kHz and hold it near to the EC86) .
The oscillation happens because of the high gain and low capacitances of the EC86. You can help with some precautions:
- only use one grid pin, and one anode in.
- remove the socket contacts for the anode and grid positions you do not need. (The extra metal increases coupling, and makes oscillation more likely).
- use ferrite beads on the grid, and anode wires, very close to the socket.
- make the anode wire as short as possible.
- connect 1µF capacitor (stacked-film construction type) between the anode power supply + and -. Connect directly between the Anode load, and the cathode resistor. Make the wires short. (This reduces the effective distributed inductance of the anode circuit).
Hello Rod,
Thank you for datailed answer. Actualy I m working on adapter from 5842 to EC86. Amplifier is Tubelab TSE II with 5842 driver stage....4K7 on grid input...
I don't know if EC86 is more sensitive regarding oscilations....?
BR,
Goran
Hello,
Just for information .... with this Rod suggestions, the adapter from 5842 to EC86 works very well ... I have a Siemens EC806S and it is a good upgrade from the Amperex AX-569. Even more fine details and body to the instruments ...
BR,
Goran
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