Another power supply question

[tom42107]

I was wondering. What is the theory behind taking a circuit that is designed for a regular, B+ power supply and changing it to a circuit that would accept a bipolar + and - supply? What would be the advantages or disadvantages? Where would the - side attach? I've included a schematic for reference. Thanks.

Tom

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/AikidoAmp3.gif.html

[PRR]

> a circuit

Can't answer the general question.

> AikidoAmp3.gif

In simple vacuum tube circuits there is NO point going to bipolar supply.

Tubes only come N-type. Their output pin is always at a DC voltage more positive than the input pin. (There are tricks but they can be painful.)

By contrast, when you have both N-type and P-type devices, it is possible to contrive the output DC to be the same as input DC voltage, which has some advantages in specific applications (not so much audio).

[amptramp]

The only advantage of having separate ground and supply voltages is with a differential or op amp where the signal ground is between the supply voltages and carries no power.  The tube amp as shown would not benefit at all.  But differential amplifiers and op amps (which are usually based on differential input stages) are better off using separate power rails so that power currents do not flow on the signal ground return as they do with a lot of single-supply circuits.  Typical op amp circuits have considerable power supply rejection for positive supply voltages and somewhat less but usually adequate power supply rejection for negative voltages.  Power supply rejection is the ratio of output voltage change to supply rail change.  For something like a triode amplifier, this is usually around -3 db and can approach 0 db as determined by the ratio of Rp and the load resistor.  For a pentode amplifier in a transformer-coupled output stage, the rejection is higher (say, -20 db for a single-ended 6V6 amplifier) due to the pentode acting as a current source.  For an op amp, it is common to see -80 db for the positive rail and -60 db for the negative rail.

So there can be advantages, but not for the circuit in your example.  BTW, congratulations on finding Tube CAD, the best tube circuit analysis site on the web.

[tom42107]

Ok. Thanks to both PRR and Amptramp for your replies. That's great help.

Tom