Help on 6L6GC Triode PP..working points..

[Maurizio]

Hello all,

I've a pair of 8K OPT from a Bell amplifier.

I would like to use them to realize a PP of 6l6GC triode wires.

Anyone can help me with the rights working points?

It's possible to reach 10-12 Wrms?

Thanks to all..!!!

Maurizio.

 

[ErikdeBest]

Hi Maurizio

here you go
http://tdsl.duncanamps.com/show.php?des=6L6
different classes of operation, with different optimal loads, and different power outputs. Trioded 6L6 seems to be good for 6W. (More power can be obtained with class 2, at the cost of increased complexity.)

Erik

 

[jon_010101]

http://tdsl.duncanamps.com/show.php?des=6L6
different classes of operation, with different optimal loads, and different power outputs. Trioded 6L6 seems to be good for 6W. (More power can be obtained with class 2, at the cost of increased complexity.)

This suggested operating point would be very conservative with 6L6GCs. With GC's, you can increase plate voltage to ~400-440V (with cathode bias) and current to 55-60mA. You can expect around 10-12W while staying mostly in class A.

 

[Maurizio]

What about fixed bias?

Hi John,

What do you think, is better to go on fixed bias?

My opt are 8k load..is this load good for the 6L6GC?

Thanks,

Maurizio.

 

[Salas]

If your speakers average below nominal 8 Ohm you will be fine with such an OPT.

 

[Maurizio]

Wich cathode resistors to read 50-60 ma?

Hi John,

wich cathode resistor i've to use to read 50-60 ma at 400 V of anode Voltage.?

Thanks,

Maurizio.

 

[jon_010101]

Re: Wich cathode resistors to read 50-60 ma?

Hi John,

wich cathode resistor i've to use to read 50-60 ma at 400 V of anode Voltage.?

Thanks,

Maurizio.

That would be about 35V-38V on the cathode -- 35V/120mA to 38V/100mA -- so, somewhere between approximately 300 and 400 ohms shared between both tubes. But I would suggest designing for some adjustment capability for balance and total bias current. Balance of current between the tubes is very important for low distortion. Perhaps look at some Williamson amplifier schematics, for example.

Or, you could use fixed bias. If you design it to be adjustable from -35 to -45V on the grid, you should be able to find a good bias point. Remember that the total voltage across the plate is higher in fixed bias (since you don't have the bias voltage across the cathode resistors).

Good luck!

6L6 data sheet

Also, 8k is a great load for a 6L6 in triode -- low distortion, and plenty of damping factor. It will need the ~400 volts though!