Date: Thu, 26 Sep 2013 17:31:43 -0400 (EDT)
From: "L L bahr " <pulsarxp@embarqmail.com>
To: Manfred Mornhinweg <manfred@ludens.cl>
Cc: amps@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
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