Rich, Ian & all...
Am I missing something? There's no reason for the cathode and bias circuit
to go way negative when the "glitch resistor" is in the negative HV lead
and a +HV arc occurs.
Putting the resistor in the negative lead means only that the -HV POWER
SUPPLY SIDE of the resistor goes to ~full -HV during a +HV short or arc to
ground. The cathode side of the resistor should be at or close to ground
potential for negative voltage, so that the full HV drops across the
resistor.
With grounded-grid triodes we almost always apply positive bias to the
cathode(s). A cheap, husky 1N5404 or similar diode, connected with its
cathode to the cathode end of the resistor and its anode to ground, does
the job of routing fault current to ground (and protecting cathodes & bias
supplies) quite nicely.
73, Dick
When +HV arcs (or is directly shorted) to ground, virtually ALL the HV
appears across the glitch resistor until the arc, short, or voltage goes
away.
-----Original Message-----
From: Rich Measures [SMTP:measures@vc.net]
Sent: Wednesday, May 12, 1999 1:08 AM
To: Ian White, G3SEK; amps@contesting.com
Subject: Re: [AMPS] Henry 2K2
>
>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 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.
- cheers, Ian
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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