? A faster method of determining HV-RFC resonance freqs is to unplug the
amp and sweep the choke in place with a dip-meter.
>> Sounds like a neat trick, Tom, but I am not quite clear on the
>> connection between the light bulb and the T connector. Is the
>> lightbulb connected between one leg of the T connector and chassis
>> ground so that the bulb is lightly coupled to the choke via mutual
>> coupling, or do you actually connect the top of choke in series
>> between one leg of the lightbulb and ground?
>
>One connection goes directly through the T to the load.
>
>The T is ground directly to the chassis as close to the top of the
>choke as possible.
>
>A small low current bulb with wire leads connects between the open
>port of the T and the top of the choke.
>
>Everything else is left in place as close as is reasonably possible,
>including sheet metal, except all connections between the top of the
>choke and the rest of the system. Only the lamp (or an impedance
>meter) connects there.
>
>The amp is cold. The tank is set below or above the test frequency
>range so it does not act like a loosely coupled high-Q "suck-out"
>trap.
>
>You just sweep frequency slowly while keeping power low and any
>inadequacies in the coke show up as an increase in brightness. If you
>substitute a resistor for the choke you can get a very rough idea of
>the impedance, but that isn't really a necessary thing. At series
>resonances the bulb will glow very very brightly even with low
>exciter power.
>
>Now if you move the tip a screwdriver up and down the choke, you
>will find a point most sensitive to the tip being near the
>screwdriver. This is where voltage is highest, and where if you add
>capacitance or remove turns (to reduce capacitance at the that area)
>choke series resonant frequency will change the largest amount.
>
>The amount of inductance overall change can be quite small, but the
>removal of the tiniest amount of wire (reducing stray
>capacitance) can move the resonance quite a bit. That's because the
>impedance at that point is extremely high, with the choke acting like
>two high-L low-C back-to-back L-networks. That's what causes the
>series-resonance, and that's how you can find where to remove turns
>to park unwanted resonances outside desired frequencies.
>
>
>
> 73, Tom W8JI
>W8JI@contesting.com
>
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>http://lists.contesting.com/mailman/listinfo/amps
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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