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" <[EMAIL PROTECTED]> > To: "Discussion of AM Radio" <amradio@mailman.qth.net>; > <[EMAIL PROTECTED]> > 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 <[EMAIL PROTECTED]> 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@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@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@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami
