[Amps] Resistor b4 the B+ filter /glitch/ notes.

[Jim Thomson]

Date: Thu, 11 Feb 2010 18:38:17 -0500
From: Roger <sub1 at 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