>
>Wilbert Knol wrote:
>>
>>
>>> With the glitch R in the negative return, the cathode circuitry may be
>>> driven to several kV by a B+ to chassis arc.
>>
>>Good point.
>>
>>I don't like the idea of most of the HT appearing across the filament
>>transformer secondary...
>>
>Does it?
With filament-type cathodes, without glitch (meter protection) diodes, it
does.
>The current around the loop is the same, regardless of whether
>the glitch resistor is connected to the top of the capacitor stack (B+)
>or the bottom (B-minus). If we keep chassis potential as the voltage
>reference, the only difference in the second case is only that the B-
>minus end of the resistor spikes to a high *negative* voltage. The other
>end of the resistor should be held close to chassis potential by the
>usual meter protection diodes.
>
When the glitch R is connected to the neg. return, the meter protection
diodes limit the voltage drop across the glitch R. This prevents the
glitch R from doing its job of limiting current.
Thus, when the hot end of a B- glitch resistor is held close to chassis
potential, the meter protection diodes limit the voltage across the
resistor to a couple of volts. Thus, virtually no current limiting is
provided.
>The practical problem about having the glitch resistor in the B-minus
>return is therefore the need for high-grade insulation at *both* ends of
>the capacitor stack.
>
The negative end of the capacitor stack is limited to a couple of volts
above gnd potential due to use of glitch diodes in the metering
circuitry. The logical place for a glitch resistor is in the positive HV
lead.
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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