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Old 25th Apr 2017, 6:45 am   #173
Diabolical Artificer
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Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,638
Default Re: 807 (maybe) amplifier build. Now EL34

It's curious that a lot of beam tetrodes or pentodes max G2 is given as 300v like the EL84 807 and 13E1 and some like the 6DQ6B, QQV02-6 are less in the region of 250v. but a lot of these valves designed for use as AF amplifiers, so their data sheets don't give AF amplification info.

Whilst designing this amp I've had some people tell me it's ok to exceed g2 max V as long as the power limit isn't exceeded. One person said this is rubbish as this POV is given by folk who've never designed an amplifier. The general consensus is NEVER to exceed the maximum ratings given on a data sheet.
But then you look at the 807 datasheet which gives total max plate dissapation as 25w, but further on gives examples of PP outputs of 80w!

Valves are pretty hardy beasts, so I guess the best way to find out if a valve can function at Xvolts g2 or whatever is to stick it in a circuit and test it.

I ran the 807's with 400v on the screen grids but not for any length of time. As they were configured in UL on 43% taps I calculated the max power wasn't being exceeded. Still, not being rich and having a box full of 807's to test to destruction, I erred on the side of caution and used EL34's.

Andy.
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