Fixed Bias setting for 6GW8

[TIMBO]

Hi guys, This is the area I'm lacking education in...
I have a push pull pair of 6GW8, I would normally do cathode bias for these but feel they preform better fixed biased.
But when it comes to fine tuning them i don't want them to have a melt down.
http://www.r-type.org/pdfs/ecl86.pdf
This pdf has great info but not sure what i need to look at...
The PT with an EZ81 is putting out about 203v on the plates.
With the usual power valves(EL34, 6l6) there is plenty of info the give you a cathode mA reading at different plate voltages.
When it comes to these oddball valves i'm a little lost when the plate voltage is different to the above datasheet.

[2deaf]

Looks like somewhere between -5V and -6V for 31mA and with the screens somewhere around 203V, also.

[DummyLoad]

-9 to -10V with 300V G2 and anodes. use -12 to start for safe zone.


--pete

[TIMBO]

Thanks guys, Screen voltage is similar to plate voltage.
Are you able to point me to the graph that gives the info needed.

[2deaf]

I just moved the 250V line on page five over the same distance as between 250V and 300V and called it 200V.

[TIMBO]

Thanks 2deaf, This is what we are looking at...
https://imgur.com/ehhd6H5
https://imgur.com/zupftP1

[tubeswell]

Loadline for ECL86 (pentode section) is plottable on this page

https://www.vtadiy.com/loadline-calculators/loadline-calculator/


I assumed a Zout = 8k2, Vp=203, Vg2=203, Ip=31mA*  and plotted the Class AB1 loadline  Vg1 on this is about -5.8V. See attached


*quiescent current idling at 70% of Pmax.

[TIMBO]

AWESOME MATE, that's great!!!!
Thanks

[TIMBO]

Yep, 8.2k