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In Reply to: RE: Q: When is Full-Wave not Full-Wave? posted by Triode_Kingdom on October 15, 2016 at 15:34:08
FWIW, I say "full wave". What you have, in fact, is 2X 1/2 wave rectifiers wired back to back. However, the liabilities usually associated with 1/2 rectification, like "standing" DC on the trafo and only 1/2 of the waveform being "captured", are not present. The construct can exhibit low copper losses. Combine low copper losses with the cost and limitations of the SS diodes of the early 1960s and it's (IMO) obvious why H/K, Fisher, Marantz, McIntosh ... gravitated towards the "full wave" doubler.
As PSUs are inherently differential, not single ended, that very diode/cap. setup could be used for a bipolar supply and each rail would exhibit a 60 Hz. ripple frequency.
A 100% true full wave multiplier is possible, but it's complex and costly. Look at the last (full wave series-parallel) setup on the linked page. IMO, motor run parts are needed in the connections to the AC feed.
Eli D.
Follow Ups:
You lost me regarding the copper losses. The doubler causes 2X the current at the transformer's secondary for a given PS output power (vs the usual full wave supply). If the secondary wire gauge isn't upgraded to accommodate this, losses will be higher. I'm with you regarding the diodes, although they did know how to series them back then. I have an RF amplifier with a 1,500 VDC @ 1A supply from the early '60s. It's all solid-state using strings of diodes (four 811As as finals).
Yes, I've looked at a few of the other doubler circuits. They all seem to have some drawback when I SPICE them, usually more difficult to overcome than this one.
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Buy Chinese. Bury freedom.
The H/K Cit. 2 has the requisite copper mass in the rectifier winding and does exhibit low copper losses. Remember, higher AWG needed, but fewer turns.Stu Hegeman called for series wired pairs of "top hat" diodes in the "Duece". In their day, those diodes were about the best available and they were expensive.
We take 1000 or greater PIV for granted, these days. Stuff like that did not exist in 1960.
Eli D.
Edits: 10/15/16
I like doublers,especially when the transformer was specially wound for it as in the case of the Mac Mc240 and the Deuce.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
JOC, how did they make the Kilo-volts needed for transmitters, in the 1940-50s?
Thanks!
The 5R4GYB could handle powers up to a few hundred watts. Mercury vapor rectifiers like the 866 were used up to 1KW or so. Above that, commercial broadcast transmitters used larger mercury vapor tubes or high-vacuum rectifiers. The 8008 MV rectifier is rated at 10KV inverse peak and 5A peak current. The 8020 vacuum rectifier is rated at 40KV inverse and 750 mA peak. I'm thinking a couple of those would work well in my next line stage. :)
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Buy Chinese. Bury freedom.
To have KV+ rating? Or did they use a series of, say, 450VDC caps --- in a string?
I have a RF linear amplifier from the '60s with a 1,500V/1A solid-state supply. It's a choke input filter with series 450V electrolytics. I don't know what the high power broadcast transmitters use, I've never worked with them.
Incidentally, I still remember going to see the "artificial lightning" demonstration at the natural science museum in Philadelphia when I was a boy. The demo charged a large bank of capacitors, then let go when there was enough voltage to arc across the gap. During the demo, there was a huge bang, following which a block of wood in the path of the arc literally disappeared. The high-vacuum rectifier they used was about three feet tall, lit up like a bunch of 100W bulbs. Yowee!
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Buy Chinese. Bury freedom.
Scary, just thinking about it. Boy, to be a tech in those days!
8^)
Steve
They were using tube rectification in those days and they were good sized rectifiers along with the power supply iron and the modulator iron.
Take a look at this Collins broadcast transmitter manual.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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