JanusRec
Well-known member
Hi everybody,
I have a really nic tube pre design from a german pro audio magazin using a EF98 pentode and optinally a ECC86 double triode for an alternative sound or as a second stage. My plan is to switch the tubes with relays (already designed a pcb and everything) but I left them on the schematic to keep it simple:
So here are my questions:
As you can see the original was designed for +24V supply voltage (they made the thing for a switched wall supply) and drop it to soemething like 6 to 10V with R22, R23 and R30. But I'm going to use a linear supply with about 15V or 18V, so I can use the same power rail for the tubes and the output stage which consists of a OPA2134 and a DRV134.
1. How do I calculate R22, R23 and R30 and what kind of voltage drop is happening in the tube, respectively? I know ohm's law, but as it seems that's not sufficient for this case
In the audio mag it sais you can adjust the gain of the EF98 via R29.
2. How do I calculate the voltage gain? I guess it has something to do with biasing and the katode voltage, but in the data sheet I found only charts for the anode current... So I'm ignoarant in how to use tube data sheets. Please illuminate me ;-)
Thanks for your help,
Sebastian
I have a really nic tube pre design from a german pro audio magazin using a EF98 pentode and optinally a ECC86 double triode for an alternative sound or as a second stage. My plan is to switch the tubes with relays (already designed a pcb and everything) but I left them on the schematic to keep it simple:
So here are my questions:
As you can see the original was designed for +24V supply voltage (they made the thing for a switched wall supply) and drop it to soemething like 6 to 10V with R22, R23 and R30. But I'm going to use a linear supply with about 15V or 18V, so I can use the same power rail for the tubes and the output stage which consists of a OPA2134 and a DRV134.
1. How do I calculate R22, R23 and R30 and what kind of voltage drop is happening in the tube, respectively? I know ohm's law, but as it seems that's not sufficient for this case
In the audio mag it sais you can adjust the gain of the EF98 via R29.
2. How do I calculate the voltage gain? I guess it has something to do with biasing and the katode voltage, but in the data sheet I found only charts for the anode current... So I'm ignoarant in how to use tube data sheets. Please illuminate me ;-)
Thanks for your help,
Sebastian