EL34 screen voltage

[RWood]

I was looking at data sheets on EL34 in AB1 PP operation.
At 475Va, Vg2 should be around 400 with Vg1 at -36v.
The 1987plexi schem I followed precisely yields Va=482, Vg2=480 with Vg1 at -36v.
I checked another "Ceriatone" which yielded Va=478, Vg2=476, Vg1=-35v.

Both amps held Screen to only a couple of volts below plates with the same PT, Choke and Screen resistors.
Is the Data sheet's 75v difference that conservative or am I missing something?

[Structo]

Yeah the choke doesn't seem to drop much voltage on the screens at idle.

Maybe it is more dynamic in that it opposes a change in current when a signal is present.

I don't know, a lot of amps were made that way.
Of course we know that modern tubes are not as rugged as vintage tubes were, so they don't tolerate higher voltage/ current as well.

I haven't tried the JJ 6V6GT yet.

I have a pair of Sylvania 6V6GT silver tops,that my Hammond amp came with, still going strong.

[jelle]

http://www.oestex.com/tubes/screens.htm

More than you ever wanted to know on screen grids, pentode operation, and plate/screen grid DC voltage.

jelle

[pdf64]

Great link, thanks!

More than you ever wanted to know on screen grids, pentode operation, and plate/screen grid DC voltage

That's a contradiction in terms

[tubeswell]

What you said about high voltages and modern tubes, I've tried running JJEL34s and New Sensor 'Svetlana' EL34s at 600 on the plates and even with 350 Screen volts and they don't seem to last very long (and that's with 1k Rg2)

[Roe]

with 1k screen resistors the voltage drops significantly under load.

[matt h]

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