Connections to beam mini-plates to triode an 813 ?

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W3RSW:
The ol' twin 813 rig construction is coming along fine but here's a proposed modulator question.  I feel I'll need more strap than the current 811A's (at 1500) volts are providing. -Well, headroom anyway.

In an audio amp using 813's as triodes do you just strap the beam forming plates together with the other grids or would it be more efficient to ground the mini beam forming plates? 

I'm aware that you can make a tetrode into either a hi mu triode or low mu triode by tying all the grids to either the 1st grid or all the grids except gr.#1 to the plate.  Also aware of the 20k jumper from screen to grid (signal to screen) lashup in triode service but wonder about the beam forming plates.   

Thanks.
Rick

WBear2GCR:
The main trick is to not exceed the current ratings of the respective "grids".
Afaik.

But if you need swing, you'll get the most power out using it with a screen supply.

             _-_-bear

KI4YAN:
The beam forming plates MUST be grounded if you want anything resembling the power of a beam tetrode. If you tie these plates to a positive supply, or to the other grids, you WILL nuke the tube at modest power levels. Tying the plates to the grid, you will get an uncontrollably high mu tube anyway.

To properly triode a beam tetrode, you'd ground the beam forming plates, and then tie the screen to either the plate, for a low mu triode, or tie the screen to the grid, for a high mu triode.

k4kyv:
I forget where I first found the info on triode connecting the 813.  I recall strapping together the screen and control grids.  That way it would work like a zero-bias  triode.  I don't remember what I did with the BFP's.

Does anyone remember where this information first came out?  The tube data in ARRL handbooks from the 50's describe using the 807 as a triode by connecting the grids together with 20k resistors and feeding the audio to the screen grids.  The BFP's in the 807 are internally connected to the cathode.  But those handbooks do not contain any information about using the 813 as a triode.

I am thinking the original circuit with the 813 may have been published in GE Ham News.

The Slab Bacon:
From what I have seen over the years, typically the screen grid was tied to the plate in smaller tubes for low power class A amps, but the screen and control grids were tied tobether in one fashion or another and driven for high power class B type applications.

I question whether it would be better to tie the BFPs to the grids or to ground them. I somehow think they would be better grounded or even kept at a slightly negative potential to keep the electron beam focused onto the plate properly.

                                              the Slab Bacon

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