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Author Topic: Want to build a tube full wave bridge rectifier  (Read 7887 times)
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kv5i
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Me & best friend John-W5ZKT(SK)


« on: January 30, 2015, 01:43:28 AM »

I am restoring a home brew amp that my best friend left me. Can you steer me to parts and articles to help me build it? I have all QST, CQ, Ham Radio, and 73's, plus several Bill Orr handbooks. I need to supply 5-7.5kv at 1amp.
73,
Ed
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There are more things in heaven and earth, Horatio,<br />Than are dreamt of in your philosophy. <br />- Hamlet (1.5.166-7), Hamlet to Horatio
w1vtp
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« Reply #1 on: January 30, 2015, 10:02:46 AM »

You will need three filament transformers[1] to build a full wave bridge PS.  9th edition of the west coast handbook The Radio Handbook 9th ed... pg 312

One word of caution: most old style grounded center tap transformers are not properly insulated to run them in full wave bridge config...  the center tap will short out to ground blowing the transformer.

___________________________

[1]  See attached, Kenyon S 9883


* kenyon 9883 (1).jpg (741.76 KB, 1492x1624 - viewed 523 times.)

* KENYON S 9883.jpg (1143.68 KB, 4928x3264 - viewed 602 times.)

* FULL WAVE BRIDGE CIRCUIT.jpg (138.97 KB, 1479x1227 - viewed 473 times.)
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KA2DZT
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« Reply #2 on: January 30, 2015, 11:12:04 AM »

I have a single xfmr that will light six 872As
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N2DTS
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« Reply #3 on: January 30, 2015, 11:15:15 AM »

That is doing it the hard and heavy way.
4 little solid state bricks would do it, or all the big filament transformers and large very high voltage tubes in a huge heavy setup, then add big chokes and oil filled caps.

Then there is the mercury vapor warm up times/flashover  and toxic waste/contamination to worry about...
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Detroit47
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« Reply #4 on: January 30, 2015, 11:21:23 AM »

The B&W L1000 amplifier uses a full wave bridge.
http://bama.edebris.com/manuals/b&w/l1000a/
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w1vtp
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« Reply #5 on: January 30, 2015, 12:53:22 PM »

The B&W L1000 amplifier uses a full wave bridge.
http://bama.edebris.com/manuals/b&w/l1000a/

Yup - it's basically the same circuit I shared.   Interesting filament transformer, huh?  The three required filament windings on the same transformer.  The hefty requirements that Ed has specified eliminates a lot.

Ed:  I have to agree with Brett - using solid state rectifiers would certainly cut down of the effort.  You could use some blue LEDs to provide the MV effect (kidding)
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N8ETQ
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Mort


« Reply #6 on: January 30, 2015, 01:47:37 PM »

  Hey Ed,


         You may want to consider a voltage doubler. Thats
what all the current production and late production Amps
are and have used.  Commander, Ameritron, BTI, Dentron all
used them.

         The strings of 450V caps simplify such things as
Bleeder's and HV Metering. Power it up with "Zero Cross"
SSR's and throw away the step start too. No center Tap
issues with the Plate iron either.

         The diode stacks are cheap and easy to construct
and I think the DC still pulses at 120cy.

         If thats not enough "Good News" for ya' add the
fact that this thing will weigh about 100 LBS less than
inefficient, chemical job as originally designed.

        You could probably hide the whole thing under
the chassis if you need "The Look".

GL

/Dan

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w1vtp
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« Reply #7 on: January 30, 2015, 02:19:18 PM »

Ed

Could you share the RF deck, modulator tube line up?  That would help us visualize in our minds what would work for you

Al
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Detroit47
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« Reply #8 on: January 30, 2015, 02:21:12 PM »

Ed

Do you have the plate iron already? You stated that you needed a full wave bridge so I take it you have already have the plate iron. I would stay away from voltage doublers unless that is the only iron you have. They are prone to voltage sag under load as well as ripple. I have never built or seen a big amp with a doubler. I am aware that a lot of commercial stuff goes that route, but as far as I am concerned the Ameritron stuff is over priced and cheaply made. The regulation is dismal and can never compare with a bridge with L input. I am sure that a lot of people will disagree with me. I have never seen a dielectric unit or broadcast transmitter use one. I have always said over build once instead of fixing it later.

John N8QPC
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KA3EKH
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« Reply #9 on: January 30, 2015, 04:32:47 PM »

Wow, big plan. 5 to 7 kV input at 1 amp that’s 5 to 7 kW input power that would still be around 2 kW output at 30% efficiency. All the old designs and broadcast transmitters I have worked with were designed around center tap transformers and two tubes for full wave that way but wondering if you need to go back and take a look at the design because that’s a hefty power requirement. Most of the old time stuff I dealt with had plate inputs of around 2 kV or so in the hundreds of mills. What kind of PA tube is in there or how many tubes? Things like the 4-1000 start to melt above 6 kV@ 0.7 A, What’s the highest plate voltage anyone around here has run? I have had IOT running at 33 kV in commercial television service but highest plate voltage ever used for Ham stuff was only around 2,500 DC.



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flintstone mop
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« Reply #10 on: January 30, 2015, 06:35:58 PM »

ED ,V5I,
Let's see this nice amp. 5-7.5kv WOW @ 1A??

Fred
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Fred KC4MOP
N8ETQ
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Mort


« Reply #11 on: January 30, 2015, 07:55:46 PM »

    Maybe the guy needs a full wave rectifier..  3.5 kv
would be about right.  Little Amps like the BTI/Hafstrom
LK2000 with a 3X1 used about 2600 out of a doubler.

     Yeah, Ok for the car, wouldn't want it in the house.

/Dan




What kind of PA tube is in there or how many tubes? Things like the 4-1000 start to melt above 6 kV@ 0.7 A, What’s the highest plate voltage anyone around here has run? I have had IOT running at 33 kV in commercial television service but highest plate voltage ever used for Ham stuff was only around 2,500 DC.






* Hafstrom 005.jpg (881.03 KB, 3648x2736 - viewed 569 times.)
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John K5PRO
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« Reply #12 on: January 31, 2015, 02:48:28 PM »

I run 12 kV for driver tetrode and 23 kV for final tetrode in new rig at the particle factory. I know some hams who are playing around with 4CX15,000s. Those can handle almost 10 kV DC. Most of us are happy with less than 4 kV though. The Collins Power Rock AM transmitters were PDM with tubes, and the 1 kW used -8500 volts while the 5 kW used about 15 kV.

Instead of using tube FWB, has solid state been considered. A lot simpler, not needing an isolation filament winding for each tube.

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Patrick J. / KD5OEI
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« Reply #13 on: February 01, 2015, 12:11:47 AM »

Tube rectifier is going to be interesting.

The 6894 and 6895 rectifier are rated 20KV/1.8A. They are about $100-$200 each NOS, not usually found surplus or used/cheap.
The 673 or 575 rated 15KV/1.5A  might work, are cheaper NOS and are easier to find used, It depends on your circuit, demand for output voltage, and how much reverse voltage you make.
You will have a possibly problematic issue with peak rectifier current unless you use choke input filtering or a CLC filter with a -small- input cap.
Solid state may be easier for the higher voltages. I personally like 673s & 575As but don't have any to spare.


It looks like you either need a custom transformer with several taps, or maybe you can use 2/3 of a surplus 3 phase transformer out of some commercial big rig. There are sometimes TMC 10KW units parted out. Those ran 7500V and a 4CX5000. The plate transformer might be useful. Also parted out regulated HV supplies from the semiconductor industry, for example in Gainesville TX there's a supply with the regulator tube removed but 3 phase HV transformer still there, maybe the solid state rectifier, and it was a 12KV 1A continuous duty regulated power supply. Might go with my ML-892 if I had a boiler for it but that's too much esoterica for me. Point is that HV transformers can't be so rare - check the industrial surplus.

People here part out stuff all the time. If you know what you want, the wanted ad section will usually turn it up! That's the best.  Grin
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WTF-OVER in 7 land Dennis
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« Reply #14 on: February 01, 2015, 02:19:14 AM »

I can't resist the allure of the blue tubes either, thumping along under load Cheesy

We have a plan of action, full speed ahead!

73DG
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