[AMRadio] High Voltage Power Supplies


bcarling at cfl.rr.com bcarling at cfl.rr.com
Sun Oct 30 13:41:37 EST 2005


They tell me that with some of the newer diodes you don't need all 
of those equalizer resistors and caps.

Back in the 1970s I regularly ran a pair of 4-400As at about 2.8 to 
3.2 KV.  The diode strings consisted of eight per leg, rated for 
1000V p.i.v. at 2.5 A - and I think they blew out about every three 
months or so!

I guess the other gentleman was probably about right with his 
suggestion of a 10 KV rating for the string!

On 30 Oct 2005 at 11:07, Ed Swynar wrote:

> Hi Jim,
> 
> Many thanks for all the info!
> 
> Well, mine is the "classic" late 70's era string of 7 diodes per leg, each
> paralleled with a resistor / disk capacitor combo. The transformer is,
> indeed, centre-tapped, & the design is full-wave rectification, the output
> of which goes directly to a series of "parallel resistor-equalized"
> high-voltage electrolytics.
> 
> The transformer itself is a classic --- an old Fred Hammond job, with a cast
> iron(!) frame! The thing weighs-in at a "mere" 90 pounds! I got it surplus
> NOS from an old surplus house in Montreal some 30 years ago now...
> 
> I took a suggestion of Bry's, Jiim, & placed an RCA plug-in type surge /
> transient suppressor that I happened to have available between the p.s. &
> the AC outlet --- that is one thing that I'd never done before. If / when
> the supply fails again in future, I'll most likely "upgrade" the silicone
> string with some of the newer, more robust chunks of silicone that were
> simply unavailable 30-odd years ago...
> 
> ~73!~ Eddy VE3CUI - VE3XZ
> 
> 
> 
> 
> ----- Original Message -----
> From: "Jim Candela" <jcandela at prodigy.net>
> To: "Discussion of AM Radio" <amradio at mailman.qth.net>;
> <glowbugs-list at piobaire.mines.uidaho.edu>
> Sent: Sunday, October 30, 2005 9:42 AM
> Subject: Re: [AMRadio] High Voltage Power Supplies
> 
> 
> > Eddy,
> >
> >     It might be helpful if you describe that power
> > supply topology. Is it full wave with transformer
> > center tap, full wave bridge, and is the filter a pi
> > type, choke input filter, etc. If this is an option
> > for you, make a sketch, and scan it into a JPEG file,
> > and upload it to the net soemwhere. I have net space
> > if you email it to me. This way we can all look at
> > your schematic, and comment better without guessing.
> >
> >    In general diodes fail from two transient factors.
> > The first is current surge, and the second is
> > avalanche reverse voltage breakdown. Since you added a
> > step/start circuit already, the current surge issue
> > should be contained. That leaves reverse breakdown. As
> > Brian mentioned, a transformer primary varistor (like
> > V130LA10A, for 115 volts, or V250LA10A, for 220 volts)
> > might help from power line transients.
> >
> >     If you look at the Bill Orr handbooks around 1970,
> > Bill goes into detail describing diode failure modes,
> > and ways to protect them. This includes a custom
> > series R-C across the transformer secondary, and
> > across the filter choke (if choke input). Today's
> > diodes are tougher, and this precaution is often
> > unnecessary so long as good diodes are used, and the
> > diode PIV rating is at least 2X what the formulas
> > state you need. However diodes like the 1N4007 (1A 100
> > PIV) need protection, whereas diodes like the 1N5408
> > (3A 100 PIV) are a lot more rugged. In researching
> > diodes, look for the term "controlled avalanche".
> > These are the best because they can take repetitive
> > PIV spikes beyond rating without turning into a piece
> > of wire. The 1N4001 to 1N4007 series are not in this
> > catagory. Unfortunately the data sheets sometimes omit
> > the "controlled avalanche" term.
> >
> > Regards,
> > Jim Candela
> > WD5JKO
> >
> > --- Ed Swynar <gswynar at durham.net> wrote:
> >
> > > 'Morning All,
> > >
> > > I'm curious as to why I have to replace the silicon
> > > diode strings in my 2500 VDC power supply about
> > > every 8-10 years, or so...I just went through the
> > > exercise again early this morning --- turned on the
> > > B+ to my 2 x 813 linear, & got nothing back for my
> > > trouble but smoke from inside the enclosed p.s.
> > > unit...
> > >
> > > Opened it up, & the resistor across the relay in my
> > > time delay circuit --- transformer primary side ---
> > > was fried. I checked the conductivity of both legs
> > > of my diode string (it's a full-wave set-up), & sure
> > > enough, one leg was A-OK, but the other displayed
> > > conductivity on BOTH sides of each diode...not good.
> > >
> > > Is this the reult of transients / voltage spikes
> > > somehow "overwhelming" the diodes...?
> > >
> > > It used to be more frequent prior to the
> > > incorporation of the delay circuitry --- but,
> > > despite its presence, this HAS to be at least the
> > > second time that a re-build was in order.
> > >
> > > Any thoughts re. a dose(s) of possible "preventative
> > > maintenance" for the future...? I'm at a loss as to
> > > anything else here that I might try...
> > >
> > > Thanks in advance...
> > >
> > > ~73!~ Eddy VE3CUI - VE3XZ
> > >
> > >
> > ______________________________________________________________
> > > AMRadio mailing list
> > > Home:
> > > http://mailman.qth.net/mailman/listinfo/amradio
> > > Help: http://mailman.qth.net/mmfaq.html
> > > Post: mailto:AMRadio at mailman.qth.net
> > > AMfone Website: http://www.amfone.net
> > > AM List Admin: Brian Sherrod/w5ami
> > >
> >
> > ______________________________________________________________
> > AMRadio mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/amradio
> > Help: http://mailman.qth.net/mmfaq.html
> > Post: mailto:AMRadio at mailman.qth.net
> > AMfone Website: http://www.amfone.net
> > AM List Admin: Brian Sherrod/w5ami
> >
> 
> 
> ______________________________________________________________
> AMRadio mailing list
> Home: http://mailman.qth.net/mailman/listinfo/amradio
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:AMRadio at mailman.qth.net
> AMfone Website: http://www.amfone.net
> AM List Admin: Brian Sherrod/w5ami





More information about the AMRadio mailing list

This page last updated 20 Oct 2017.