>
>Rich Measures wrote:
>>
>>
>>>
>>>Picking up on one of Rich's remarks:
>>>
>>>>Henry's glitch-R in the neg. HV
>>>>lead is a mistake. A glitch R should be added to the pos. HV circuit.
>>>
>>>It doesn't really matter which end of the HV circuit the glitch resistor
>>>and HV fuse are - unless the designer thinks that putting them in the
>>>negative return rail requires less insulation. In fact it requires
>>>*more* insulation, because a "crowbar" short from HV+ to chassis will
>>>tend to push the return rail down to *minus* the normal HV.
>>
>>>To avoid breakdown, the negative rail and the negative end of the
>>>capacitor stack therefore need to be insulated to the same standard as
>>>the positive end.
>>>
>>? The sticky wicket
>
>You're obviously a bigger cricket fan than I am, Rich!
>
>Where were we...?
>
>>? The sticky wicket with putting the glitch-R in the neg. hv circuitry
>>is that the filament transformer/cathode circuitry must be insulated for
>>several kV. However, allowing the cathode to rise to several neg. kV
>>during a HV+ short to chassis is likely to cause an arc to the
>>grounded-grid. Thus, it is my opinion that it matters which end of the
>>HV circuit the glitch-R is in.
>
>The cathode doesn't go strongly negative at all - it stays around
>chassis potential, much as it would if the glitch resistor is in the
>positive lead.
? provided that the glitch-R is placed on the neg. side of the
anode-current mete shunt-R. .
>The point that dives several kV negative at the start of
>the glitch is where the negative (power supply) end of the resistor
>connects to the negative end of the smoothing capacitor.
>
>In both cases, the full HV appears across the glitch resistor, as it's
>intended to, and the resistor limits the maximum current that can flow.
>
? Is there a tube manufacturer who does not recommend placing the
glitch-R in the positive side of the anode supply?
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|