Hello Folks, my tube power amp transform have 3 separated 6.3vac o/p are 2A, 5A, 5A respectively, so I just use 2A with Lm317 regulated DC 6.3VDC for voltage elevation connection to B+, and other two 6.3VAC direct supply to power tubes. My question is the whole amp just need a single voltage elevation circuit or not ? Or should have all filaments supply do the same this connection ?
If I deploy 6.3VAC virtual ground by two 100R resistors to ground, then how to make upper connections?
If I deploy 6.3VAC virtual ground by two 100R resistors to ground, then how to make upper connections?
It is usual, if you require elevation, to connect the heater virtual ground to up to 50volts DC either from the cathode resistor of the output valves or make up a ladder to give you around 45 volts from the HT supply and ground from a potential divider.
500v DC would be 100k feed and 10k to ground. Decouple it with a 22uF capacitor to ground. etc.
500v DC would be 100k feed and 10k to ground. Decouple it with a 22uF capacitor to ground. etc.
Thanks Jonsnell your advice.
However, I need 3 set of 6.3V do the same arrangement? Or just single set have this connection?
However, I need 3 set of 6.3V do the same arrangement? Or just single set have this connection?
Power amp tubes don't need heater elevation, cathodes are grounded (at least for AC) so there's no noise entry. Signal tubes probably do if a split-load or long-tail phase inverter is used. One side grounded is fine for power tubes - but don't use chassis as a conductor.
Thanks Tom your advice.
You said one side grounded, does it means only single power tube do this elevation.
You said one side grounded, does it means only single power tube do this elevation.
Elevation of heater winding is used to reduce heater-to-cathode voltage, and to reduce heater-to-cathode hum coupling (the latter probably only matters for the first voltage amplifier stage. Power tube heater windings can have one side grounded - makes voltage measurement easier, as one meter lead can clip to the chassis. Obviously, if you only have one heater winding, it should be elevated. With multiple windings, the one for small signal tubes should be elevated, has no benefit for power tubes.
If you use DC filaments you do NOT elevate them, what for?
And does LM317 have any ground reference to get 6.3VDC?
6.3VDC relative to what?