Tube differential gain

[mbrennwa]

2- What kind of CSS doesn't need negative voltage ?

You could use "always on" FETs to make a CCS for the LTP tail, as shown in the attachment. You can set the current by changing the Rset value. I use this in the LTP front end in my SuSy T. PuckFo amp, and it works very well.

 

[wayne]

Here is a circuit that works just fine with no negative supply. The LM334 is a programmable current source.

 

[wg_ski]

Works ok with any tube requiring several volts of cathode bias at the operating current. When you’re down to a volt or two with a high mu tube you don‘t have enough headroom in the CCS. If you‘ve got degeneration resistors to set your gain to something less than the maximum you lose even more. Just a 5 or 10 volt negative supply would ensure you always have enough headroom, even if your CCS drops a minimum of two volts. An unused 5 volt rectifier-filament winding would work, or run an MJE340 CCS off your bias supply.

 

[mbrennwa]

Works ok with any tube requiring several volts of cathode bias at the operating current. When you’re down to a volt or two with a high mu tube you don‘t have enough headroom in the CCS.

Yep. You'll have to raise the grid bias to allow enough headroom for the CCS (example attached).

 

[legarem]

Thanks a lot for your help.