How can I add a balanced input to a tube amplifier?

[Johnny2Bad]

More details, please, with regard to that Power Supply?

 

[Kay Pirinha]

Attached is a common circuit for creating a CCS with an LED and transistor. In my case, the cathode is high enough (about 5v) above 0v that I can supply the LED voltage from the cathode.

Don't do that. If it works at all (does the common cathode current exceed those 5 mA that is needed by the LED?), it decreases the total impedance, as seen by the cathodes, significantly, presumably even below the value of an appropriate fixed resistor.

Best regards!

 

[lazzer408]

More details, please, with regard to that Power Supply?

Regulated soft-start 6.3vdc for filaments. ~300vdc unregulated B+ and ~250vdc unregulated for preamp.

 

[lazzer408]

Don't do that. If it works at all (does the common cathode current exceed those 5 mA that is needed by the LED?), it decreases the total impedance, as seen by the cathodes, significantly, presumably even below the value of an appropriate fixed resistor.

Best regards!

The LED sees less then 1ma.

 

[Kay Pirinha]

Even then there's abslutely no necessitiy to put it in parallel with the CCS. Best is to return the CCS to an auxilliary negative supply that your fixed bias amp already has. Then connect a resistor of proper value from the LED's anode to ground.

Best regards!

 

[jerrylong]

I am trying to add balence input now, this is really helpful