[AMPS] HV board indicators.

[nospam4me@juno.com]

re:  Neon indicators in the hv supply 

I've always relied on a quality meter to detect voltages, 
but I thought the addition of an Neon Bulb - resistor 
combo in the ps was a pretty neat poor mans HV 
indicator.  

One side bar is the ~70 volts required to fire the NE-2, 
below that amount the bulb is dark and one might 
be fooled, leaving a nice surprise for the quick handed 
screw driver types. 

I've now retro'd the circuit into an LED version, with 
current limiting and piv protection (for the led).  The 
LED continues to indicate voltage present in the HV 
to much lower values.  

I still have and use the meter first, but the LED's sure 
are nice to look at and a quick visual reference. 

cheers
skipp 

>From: Peter Chadwick <Peter_Chadwick@mitel.com>
>:I've asked before on this topic without an answer - maybe lucky this
time.
>:What's the failure mode for SSRs? Do they fail short circuit or open?

>Working on the basis that 'Murphy rules - OK?', I've always assumed that
the
>failure mode is short circuit, and then figured that mechanical relays
can at
>least be seen to be stuck closed (well, sometimes) and gone for those.
Plus a
>neon indicator across the bottom electrolytic of the HV stack, a circuit
breaker
>on the AC feed so the amp can be totally isolated, and final line of
defence, a
>shorting stick. Even so, I never feel happy about touching the HV lines
after
>all that....but if the SSR fails short, it could be inconvenient at
best.

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