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November 28th 08, 05:49 PM posted to rec.radio.amateur.homebrew

Stev eH[_11_] Stev eH[_11_] is offline

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Passive grid linear

wrote:
On 28 Nov,
ken scharf wrote:

200W from a PAIR of 813's? You must be running them with less than
1.5KV on the plates. That's the problem with 813's, they don't live up
to their potential (pardon the pun) unless you run them with lots of HV.
The point though is that in conventional grounded grid (all three
'grids' grounded) you still don't need a SG supply and the drive power
should be about the same.

I could get well over 400w (probably nearer 800w) out of mine, with 2,5-3KV
on the anodes.

With G2DAF mode I found the screen grid supply (from the RF drive) produced
lots more TVI than when conventionally used in class AB2. That's why I
changed. I used separate screen and bias supplies, but made sure the anode
supply was present before the screen was energised.

That's with 10W of drive (From a 10W radio) and 2KV on the anode,
maximum output is around 600W with about 40W of drive. You can wet away
with over 3KV on the anode if you are careful.
If you introduce a 4:1 transformer on the input the drive required is
far lower.
I have a KW500 with a single 813 in grounded grid, it produces 40W with
10W in and is a bad load for a transistor TX (No tuned input as it was
designed to work with a valve TX). With passive grid you don't need a
separate tuned input for each band so it keeps it simple.

Steve H

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