2X "6" V. tubes of the same type and same production run, with their heaters in series, will be fine connected to the toroid. You could bias the junction point of the 2 heaters off B+, for noise control.
Take the center connection of the two heaters, the two that you connected together and are not connected to the transformer, and place about 50V of bias using a resistor divider from B+. It's not a requirement, but can reduce hum.
You can ground the centre point but, if it is a high gain circuit such as an MM or MC preamplifier, elevating the filament can yield a useful reduction in hum as previous posters have said.
In addition to biasing that point off B+ with a resistive voltage divider, you ground that point via an electrolytic cap. of several μF. As the other posters stated, the network of 2 resistors and 1 cap. reduces vulnerability to hum and other noise.
+1 on the cap.
If you want, you can calculate its value based on the resistance. But, I'd probably just make it 10uF and be done with it.
Last edited:
- Status
- Not open for further replies.