Brian, K3VR wrote:
"I get about 4400-4600V on the plate under load, depending on line sag. I
can
only get about 280 ma of plate current, though. Grid current can be up to
100
ma depending on drive. Filament V is 7.5 under load. The xfrmr is a 3500V@1
A, Peter Dahl with a voltage doubler: 2 oil filled caps in parallel. "
Note: a 3500 VAC xfmr with a doubler would give about 10KV no-load. Either
your transformer is mis-marked, or you're using a bridge. In that case,
your
voltage output is not terrfic, but OK.
My experience with the two 4-1000A amps here is that a good tube operating
correctly has about a 3:1 ratio of grid to plate current. By "grid
current"
I really mean grid and screen total (both grounded) Note that some 4-1000A
designs ground the screen but read the grid, in which case the ratio
doesn't
hold. Also, with certain metering schemes, "plate" current might actually
be "cathode" current, so again the 3:1 ratio doesn't hold.
If you're driving your amp with 100W, the results you're seeing are about
all you can expect. Up here in Michigan, experience of many amateurs is
that
a 4-1000A with 6KV on the plate is a 13 dB gain box (i.e. whatever does in,
twenty times that comes out). I tried running one of my 4-1000As at 3300V
and could only get 1KW before the grid current went out of sight. Really
makes you love 3-1000Zs...
73,
Dave/K8CC
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