[Amps] Other HV rectifier diodes

[Jim Thomson]

Date: Thu, 26 Sep 2013 17:31:43 -0400 (EDT)
From: "L L bahr " <pulsarxp at embarqmail.com>
To: Manfred Mornhinweg <manfred at ludens.cl>
Cc: amps at contesting.com
Subject: Re: [Amps] Other HV rectifier diodes

If you have a 1000 volt power supply, what should the diode stack voltage rating be?  I have heard it is good practice to make it 4 times the voltage of the operating voltage.  In other words, make the diode stack good for 4000 volts for a 1000 volt supply.  Is this correct?  Also, would there be a difference when a choke input is used VS capacitive input?

Lee, w0vt  

## Most commercial  FM –AM  broadcast TX amps use TRIPLE the piv.   In theory, you could get away with just 10-20%  more piv.  That is, until the spikes, transients, surges etc  come down your 240 line..from the street outside. 
The filter cap might be able to absorb some of the spikes, but don’t count on it.  You can also wire a 250-270 vac MOV across the primary of the plate xfmr.   But a MOV typ wont begin to conduct steep fast rising transients until double its V rating.
Hence using  triple the PIV rating for commercial applications.  The older arrl books said to use at least double the piv, since movs don’t conduct until  double the mov rating.... but that leaves it on the edge. 

##  6A10s  are so cheap these days, I just use triple the piv..and be done with it..... +  a big  bolt down   250-277 vac rated MOV  across the primary.  These are the bigger movs, that bolt to the chassis  with a pair of machine screws....
and also use a pair of machine screws for the wiring connections.  Mouser sells em cheap.   Like 2 inchs wide x 2 inches tall x half an inch thick.   You can also parallel the smaller quarter dollar size movs. 

##  If any movs are used, they should have a 250-300 vac rated fuse inserted in one  leg of the mov, either leg will do.    A 120 vac neon, wired   from junction of fuse + mov.....over to neutral  will suffice as the mov fuse  indicator.
IF mov ever shorts out, mov fuse blows open....and neon goes dead.  In normal operation, with a good fuse and a good mov, the neon will be lit up.   You can also get leds that run on 120 vac..does the same job.

Jim  VE7RF