>
>Greetings,
>
>I've searched some of the reflector archives as I know this topic has been
>discussed before, but I cannot find any info. I'm ondering what
>experiences others have had with respect to non-inductive resistors that
>are commercially available.... source.... manufacturer... results etc. I
>seem to recall discussions to the effect that some in that supposed
>non-inductive resistors were actually not so non-inductive in HF service.
>
** Every Resistor has intrinsic inductance, Typically, this is roughly
12nH per inch of length. Grid terminating resistance is usually chosen
so they are compatible with 50-ohm drivers/transceivers and broadband
matching transformers such as 1:4 (200-ohm out); 4:1 (12.5-ohm out), no
transformer (50-Ohms), and 1:9 (450-ohm out). The choice of which
resistance is better depends on the # of Watts available and the DC grid
bias required. For example, a tube that needs -200V bias could use a
200-ohm grid-R with a 1:4 transformer and a garden-variety 100W-rms
(200W-peak) radio. For the cleanest signal, do not operate the grid in
the positive region where it draws current. Thus, an adjustable output
radio is an advantage in AB1. Good engineering practice is to locate the
grid resistor as close to the grid as possible, use a low-L
triple-cap-bypass (such as 100pF/1000pF/0.01uF in parallel) to RF ground
the cold end of the resistor, and connect the DC bias V at the cold end
through a 100 to 1000-ohm resistor. (this assures better stability /
less surprises). Neutralized AB1 is he most stable. // See Figure 5 on
my Web site. Neutralized AB1 is also a natural for general freq.
coverage since the neutralizer-bridge's roller-L simultaneously tunes
out grid Xc for any operating freq. when input SWR is tuned to minimum
with he roller-L.
- have fun.
> ... ...
- Rich..., 805.386.3734, www.vcnet.com/measures.
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