[Amps] Results from new PSUD... resistor b4 the B+ filter caps !

[Gary Schafer]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On Behalf Of Paul Christensen
> Sent: Thursday, February 11, 2010 12:17 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Results from new PSUD... resistor b4 the B+ filter
> caps !
> 
> > It seems to me that a primary step start is a much better way to go,
> if
> > one
> > is even needed. As long as the breaker don't trip and the diodes can
> > handle
> > the peak current.
> 
> But the series R between the rectifier and filter C should still keep
> current limited in the event of a filter C short -- and hopefully,
> assist in
> protecting the rectifier stack.  That's something the step-start circuit
> cannot protect after the initial "step" sequence.

If the filters short the next thing you want to happen is for the primary
breaker to open which it should without harming the rectifiers (same as if
you have a glitch on the other side of the filters).
Even if it did take out the rectifiers, they are so cheap that they are
almost free anyway compared to the cost of the filter caps.

> 
> My "take away" from this discussion is that a distributed surge
> suppression
> approach may be best comprising of: 1) primary step-start to strictly
> limit
> filter C in-rush current, 2) series R between the rectifier and filter C
> for
> rectifier preservation during a C short; 

If you are going to place a series R before the filter then you might just
as well buy a cheaper transformer with a higher R winding. Also don't worry
about a heavy power line to the amp.

>and 3) Series R close to the anode
> for arc-fault protection of all HV cabling, inter-compartment HV
> connectors
> and components ahead of the anode.

If you want to protect the HV connector, cabling etc. then the glitch
resistor should be placed near the power supply.

> 
> Regarding placement of series R between the rectifier and filter C on a
> gg
> amplifier with a traditional elevated HV(-) return, I am still pondering
> whether that R should be broken up in equal amounts of say 10-ohm each
> between both HV terminals and the filter C.  In other words, is there
> some
> fault condition where a surge resistor placed in the HV(-) lead >between
> the
> rectifier and filter C that would assist in fault protection?

I can't think of any. You want to always keep the B- close to ground. In the
event of an arc over in the tube you do not want the B- to be able to go
much above ground.

73
Gary  K4FMX

> 
> Paul, W9AC
> 
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