Date: Thu, 11 Feb 2010 18:38:17 -0500
From: Roger <sub1@rogerhalstead.com>
Subject: Re: [Amps] Results from new PSUD... resistor b4 the B+ filter
caps !
My question becomes, will this do anything to protect the tube(s) in
case of a flash over?
If the tube flashes over you still end up dumping all of the power in
the caps into them.
73
Roger (K8RI)
### NO... it won't do anything to protect the tube[s] !!!
It's NOT a 'glitch' resistor. For a glitch R.... you have to install
a typ 50 ohm /50 W WW... in series with B+... on the OUTPUT
side of the caps. I use a HV sand fuse, on OUTPUT of B+ supply,
followed by the 50 ohm glitch R.
## If a B+ fault occurs [anode to grid, B+ to chassis/ metal, etc,
then the 50 ohm GLITCH R ..LIMITS the fault current to a safe
value. The HV FUSE, just b4 the glitch R.... INTERRUPTS the
fault current.... and does so in , 2 msecs.
## To protect HV lytics from raw AC being pumped into em, on
1/2 cycles, because one or more of the 4 x legs of a FWB shorted out...
..or one or both legs of a FWD shorted out... here is the easy fix. Install
6A10 /1N5408's in parallel with each lytic, ONE diode per lytic. Polarity
of diodes are reversed of course. In normal operation, nothing happens.
Now IF 1+ legs of ur FWB ever shorted out, and started pumping raw AC
into the string of lytics... the diodes across each cap simply conduct, and
rectify
the raw AC.. and do so directly between B+ and B- . The breaker in the 240
line
will blow open.
## I also install a 2nd HV sand fuse... between SEC of plate xfmr... and
INPUT to FWB.. [either leg]. In the above case, this HV fuse will blow open
before the 240 vac breaker blows open. Also, this 2nd hv sand fuse will
protect
the FWB, in case an oil cap shorts, or any other short/fault, between xfmr
sec.... and
HV fuse #1 [ located just prior to 50 ohm glitch]. I also use a mag
/hydraulic breaker in the
240 vac line.. with a super fast trip function.. "instant trip". With this
setup, I can cro-bar
ANYTHING, anywhere, inside the B+ supply... and only hv fuses open /breaker
pops open.
That includes short across pri /sec of plate xfmr. Short in the FWB, short
in the B+ filter,
short inside the RF deck, etc, etc.
## The above simple protection concepts has been thoroughly tested, and work.
### super fine wire, suspended taut, between 2 x standoffs, will also suffice
as a HV fuse,
just wrap the fine wire, loosely, with 88 tape. 1-2" C to C spacing, between
the 2 x standoffs.
later........ Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|