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Thoughts on these xfrmrs




 
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Author Topic: Thoughts on these xfrmrs  (Read 915 times)
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va3dxv
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« on: March 08, 2020, 10:37:36 AM »

I've been looking for a good plate transformer without much luck. But I just found these and can get 2 of them pretty cheap. 1500VA@600V. Wondering about using 2 of them in series for 1200V (600-0-600?) and using a voltage doubler. Good idea or bad idea? Thanks for any input.



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W7TFO
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« Reply #1 on: March 08, 2020, 02:03:30 PM »

That type of iron is pretty tough, with great insulation.

I've done exactly that you ask with no problems, but not with a doubler.

Too much droop, a shame to waste the low source impedance of that type trans.

73DG
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WD5JKO
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WD5JKO


« Reply #2 on: March 08, 2020, 03:43:40 PM »



  With a Full Wave voltage doubler, you will get about 1700VDC no load from one 600vac winding. A rule of thumb with the FW doubler is to boost the two capacitors MFD size to 4X that of a FW CT arrangement, or FW Bridge. Many legal limit linear amplifiers use a Full Wave voltage doubler arrangement. Those do require a good stiff AC source, and 220V primary circuit. Depending on your Caps, and load, you might get 1400 to 1500v under load.

   Running two Tranny's in series to make a FW CT arrangement has the issue where each tranny sees a current pulse during only one half of the waveform. Some transformers don't like that, and may buzz, especially if the core saturates.

Jim
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va3dxv
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« Reply #3 on: March 08, 2020, 05:13:27 PM »

Ok thanks. I need more than 1700VDC so I guess they're out of the question.
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WD5JKO
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« Reply #4 on: March 08, 2020, 05:30:16 PM »


 What if you used both transformers, and put a voltage doubler on each? Then series up the DC side to make 3400v no load, and about 2800-3000 loaded +/-?

The caps would need to be a series string of two for each one needed, 8 total...something like 330 uf @ 450vdc.

Would need a step-start for sure.

Switch the primary to 120VAC feed into 220v windings for lower power or Tune position.

Comments?

Jim
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KL7OF
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« Reply #5 on: March 08, 2020, 09:58:05 PM »

1.5 kva?   What is your current requirement?
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va3dxv
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« Reply #6 on: March 09, 2020, 06:29:00 AM »

1.5 kva?   What is your current requirement?

Much less than that would provide. I probably wouldn't need more than an amp or so.
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WD5JKO
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« Reply #7 on: March 09, 2020, 07:12:09 AM »

1.5 kva?   What is your current requirement?

Much less than that would provide. I probably wouldn't need more than an amp or so.

Holy Cow.....that info should have been in your first post! Tum Tum Steve, glad you asked. Using a FW doubler just got a lot harder since the caps will see a lot of current. Best to model, or increase the cap size ~ 5X as a SWAG.

Jim
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va3dxv
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« Reply #8 on: March 09, 2020, 10:26:37 AM »

Meant half amp but I mean, a pair of 3-500z pulls about 600ma or so and that's the biggest tube I would ever use. Probably more likely to run something smaller but it would be nice to have the overhead.
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« Reply #9 on: March 09, 2020, 04:24:33 PM »

How about this? Both transformers work on both half cycles.


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va3dxv
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« Reply #10 on: March 15, 2020, 12:45:56 PM »

Well found the spec sheet and that throws this idea out the window, it's a 600v primary and 120/240 secondary, so I'd have to use it bassackwards

Wish this stuff wasn't so hard to find!
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W1ITT
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« Reply #11 on: March 15, 2020, 01:56:27 PM »

Having been through the difficulty of finding the "right" transformer for a new linear amplifier,  I decided to give up the search and wind my own, using modern C-cores.  KF8OD has done the work and his website has two cookbook solutions right there for us, as well as good paths to design our own.  It's not  real easy nor is it particularly cheap.  I'll have about $400 in mine when I get done but the excellent Peter W Dahl unit would have cost more.   I fear that when OMs may have gone beyond the ionosphere many of their heirs may have consigned some fine transformers to the dumpster or the scrap man, hence the scarcity in the hamfest market.
https://www.qsl.net/kf8od/ccore.html
The old buzzards of yore wound or rewound transformers to suit their needs.  We have better availability of the necessary supplies so there's no reason we can't do the same while we are waiting for the Wuhan virus to run its course.
73 de Norm W1ITT
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va3dxv
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« Reply #12 on: March 15, 2020, 02:18:54 PM »

Checked out the link, thanks. Pretty cool. Someday I'd like to do that but the initial expense of materials is too much right now.

I could get the 1500VA 950V (toroidal) from Antek to my door for about $300 but that is really pushing my limits. Our dollar is pretty weak right now. If that cost you $400, it would probably cost me $600!  Angry
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kb3ouk
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« Reply #13 on: March 15, 2020, 03:56:44 PM »

Well found the spec sheet and that throws this idea out the window, it's a 600v primary and 120/240 secondary, so I'd have to use it bassackwards

Wish this stuff wasn't so hard to find!

No problem with that, i use an Allis Chalmers control transformer that had i think a 480/240 primary and a 120 secondary in my homebrew rig backwards and it works fine.
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« Reply #14 on: March 15, 2020, 10:44:38 PM »

I am curious about why some people don't like a reversed transformer, especially on the higher quality ones?

It may be in a book, something I missed.

Not suggesting any change, but merely curious if I am missing something because I've had pretty good luck except for the smallest units like the typical Radio Shack 6.3V 2A unit or equivalent, which get warm.
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« Reply #15 on: March 16, 2020, 04:56:17 PM »

Well found the spec sheet and that throws this idea out the window, it's a 600v primary and 120/240 secondary, so I'd have to use it bassackwards

Wish this stuff wasn't so hard to find!

The transformer has no idea which side is which!

Fine to run it "backwards".

Nothing to worry about.

It's wire wound around a core on a form...
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W1ITT
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« Reply #16 on: March 16, 2020, 05:31:26 PM »

While it is true that a transformer doesn't know its nose from its tail, there is the potential problem of insulation ratings.  Especially when we hams start voltage doubling we may exceed safe insulation ratings, and that is even more possible if the transformer was built to a price rather than a quality specification.  I recall a few years ago a design in an article showing a linear amplifier with voltage quadrupling!  When I was 12 or 13 years old I found that transformer insulation is not infinite.  My parents objected to the smell of flaming insulation in my bedroom.
But we are hams, and we have a wonderful tradition of operating tubes and transformers beyond their ratings and most of the time people get away with it, at least for a while.  As long as we have safely grounded equipment, properly rated fuses or circuit breakers, and a fire extinguisher in the corner, we can throw caution to the winds and give it a try....  until Santa brings a PW Dahl hipersil transformer down the chimney.
73 de Norm W1ITT
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« Reply #17 on: March 20, 2020, 08:49:05 PM »

The simple thing to do is to call the company and ask what the insulation rating is. They make a big deal of their hi-pot testing. I truthfully believe there is not an issue at 1800V on the 600V side of that thing.
http://www.marcustransformer.com/pages/quality.agreement.php
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WD5JKO
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WD5JKO


« Reply #18 on: April 02, 2020, 11:17:41 AM »



Here is an idea:

http://www.kwarc.org/bulletin/99-04/tech_corner.htm

This circuit and one of those 1000va 1000v Toroidal Antek's would be ideal here...

Or run what you got, one tranny = 1700V and two tranny's in series, 3400v unloaded.

Another reference from fellow member IN3IEX:
http://www.ing.unitn.it/~fontana/FWvx2andvx1.pdf

Jim
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