plate transformer identification

[W4AMV]

Good day,

Does anybody recognize the manufacturer of this power transformer? Thought it may be TRIAD but the part number 24R86 does not match up with anything I could find. Estimate the transformer was put into use around '75-80. Wire brush, coat a new paint good as new... after checking for any possible issues

Tnx, Alan

[KA2DZT]

Most likely a Thordarson.  I'll try to check it out later tonight.

Fred

[W4AMV]

Thank you Fred. I would like to get specs to see if this unit can handle a pair of 813's in ICAS. Would not be using the 5 V line. This was used in handling a pair of 4-400A's using a voltage doubler and seems a little light in capability.

[KA2DZT]

Probably a little light for a pair of anything.  Are you talking about SSB or AM service??  Thordarson xfmrs numbers ran up to 26 series.  Although some early xfmrs had higher starting two numbers.  The later era numbers went to 26.  The 24 series are not common, but I think I remember seeing some info on them in my xfmr catalogs, etc.  I'll see if I can look today and get back.

Thordarson made thousands of different xfmrs.  Probably more so than any other manufacturer.

Fred

[W4AMV]

I agree Fred. It most definitely is Thordarson as the model numbers line up with what catalogs I could find. I am talking CW. I was thinking along the lines of trying to pull 500 mA from it when voltage doubled. Not using the 5 V winding for anything other than relay control. Currently running a pair of 811A's from a 500 VA 480 V control transformer and key down I am at about 1 kV best case. Not sure how this unit ran a pair of 4-400A's. I do have a Berkshire transformer but its a bit too large for the amps in mind for now.

[KA2DZT]

Control xfmrs can handle a good overload with no problem as they are rated for continuous operation.  CW should not be a problem for your xfmr.  Are you going to use FW bridge rectifiers??  Some xfmrs can't be run with the CT not grounded.  If this one was run like that already with the previous service, it passed the test.

Fred

[WD8BIL]

That secondary is 1235V at 500ma (617 watts). In a doubler 617 watts will be half that current.

[w4bfs]

need to be cautious here .... how much does it weigh ?  ... if it weighs 10 to 15 pounds then it is about 350 W or VA and the 1225 V labeled is the end to end voltage and is implied to be in a full wave center tap, inductor input supply for .5 A dc around 600 Vdc continuous .... to be a 600 W xfmr it will need to weigh around 30 pounds or so .... can't ignore physics

[W4AMV]

Thanks for the inputs! Weigh in is 19.8 pounds. Not sure how this ran 4-400A's, the PS was a voltage doubler and the CT was simply not used.

My thought is this unit is a good replacement for the control transformer and the 2x811A's as the 1200 V unloaded supply I am currently using sags to 900 V key down worse case. 

Alan

[KA2DZT]

20 pound xfmr should work OK for CW.  FWB, no voltage doubler,  choke input or cap input??  Measure the DC resistance of the whole secondary, let us know.

Fred

[W4AMV]

Hi Fred,  36 ohms.

I am currently using cap input. I have 1000 uF/450V units. I usually use series R to the diode bank, 25-50 ohms. I could go choke input but rather not, my selection is limited and most of my swinging chokes are bit old and noisy.

My current thinking is FW, not doubling.

Alan

[KA2DZT]

36 ohms is somewhat low for a 1200 volt secondary.  The 36 ohms is the entire secondary, end to end, correct??  Anyway if it is, that's good, indicates the winding uses a little heavier wire than might be used in lower grade xfmrs.  You're using a FW Bridge rectifier, not a FW which uses the CT.  The 1200 volt rating you see on the xfmr should be indicating the voltage of the whole secondary and not the voltage from the CT to an end.  You might check that to be true.

Normally with a FWB rectifier you can only pull half the rated current.  The xfmr is most likely rated for choke input filter.  Using a cap input filter and you can reduce that another 30%.

Having said all of this,  you're using it for CW service, so you can overlook the half current rule.  The xfmr was most likely rated for continuous service,  add in the fact that these xfmrs can easily handle 50-100% overloads continuously,  you should have no problem with what you're doing.  Not using the filament winding also helps.  A good overall indicator is the low DC resistance of the secondary.

Cap input filters always put heavier VA loads on the primary.  Using large input caps doesn't help,  you need that series resistor to limit inrush current.

Final operational test,  hook it all up,  make some QSOs,  if the xfmr doesn't get too hot,  should be OK FB.

Fred

[W4AMV]

Hi Fred,

The 36 ohms is the entire secondary, end to end, correct??

Yes, that is correct.

I will check the V_RMS across the secondary winding and from the label on the transformer that is my understanding, 1200 V end-end with a CT connection. As I received the unit, the PS was set up for doubling, so 2400 V rms for 4-400A is reasonable while 4800 is certainly not. I just had a problem with the current rating and why I was originally after the rating, continuous or intermittent. Thus the original question, finding a data sheet. 

[KA2DZT]

Looked thru my xfmr books,  found some 24 series xfmrs.  Your 24R86 was not shown.  Even saw some 27 series xfmrs, so Thordarson later era xfmr numbers went to at least 27.  The ratings you see on the xfmr are continuous.  Even if we find your xfmr in some listing somewhere it probably won't say much more than what you see on the xfmr.

Hook it up, run it, check the temperature rise.  Not much else you can do  More of a concern would be the CT not at ground.  The xfmr was already used with the CT not grounded, so it passed this test.

Fred

[K7LYF]

Go here and ask for specs: http://www.thordarsonmagnetics.com/customTransformers.php

I saw 24r87 and 24r89 listed there.

[KA2DZT]

Go here and ask for specs: http://www.thordarsonmagnetics.com/customTransformers.php

I saw 24r87 and 24r89 listed there.

Thanks for posting that.

Seems the 24 series xfmrs were designed for cap input for the stated current rating.  So with choke input you can increase the stated current rating by 30%.  Not sure if this is true for the OP's 24R86 since it was not shown, but probably.

Fred

[W3RSW]

Here is how I test plate transformers.
I have a 25k 200 watt CT WW resistor which I can hook up as 25 k, 12.5k and 6.25k for brief periods.
Simply build up your bridge circuit, place your relatively light bleeder resistor/ filter cap string across it for your first point.
Then progressively load it heavier and plot each point on a sheet of semi-log paper of DCvolts vs. the resistors attached (or converted to amps using ohms law).

If you get a straight line, the Xfor's good all the way to heaviest load point. If it starts to droop, the knee at sag point will tell the tale.

You can also plot AC RMS without using any DC Conversion for first trials.

I've done this on an 800-o-800 at 500 ma , approx. 20 lb. potted military transformer having 105, 110, and 115 primary, used it for 1900 VDC bridge, CT floating for years on my pair of 8875 HB linear, ( 120 on 105 tap, SSB /CW ) and independently on a 811a's modulator with 120 vac on 115 tap, choke input, 1600 VDC or so out.
Tough iron. Curve just started to droop on the 6.25k load.

Ran same tests on a PDahl 3000v / 1 amp CCS showing zero droop (dv/log dI) with a far better slope showing. Really tells the tale.  I'd need a 500 ohm resistor for that beast to show a sag. . ( Exaggeration for fun and profit.)

[W4AMV]

Thanks Rick. Yes, I have something similar although not quite as focused on the measurement detail. A dozen or so 200 W 4 K ohm ceramic R's that I can series and parallel to achieve the load and power handling and then load the PS and note the drop. The initial post was motivated by a sanity check as to what sort of tube would this transformer handle. Alan

[WD5JKO]

A lot of good stuff discussed thus far. A couple of things though come to mind:

The primary is rated at 115vac. I would not assume that it will work fine at 125 vac. Might use a variac and a clamp on ammeter to look at primary current. As the voltage rises from 115 vac, at some point the primary current will rise quickly indicating core saturation. Hopefully that point is over 130 vac. If it is a little too close to your line voltage, consider using that 5v 6A winding in series (phased) such that the primary voltage rating moves up 5 volts higher. This will change the turns ratio though, and decrease the secondary voltage a bit.

The HV secondary center tap might not be insulated to float above ground. Might take the end bell off to see how the wingdings appear. Maybe there is a clue as to how things are wound, and from that clue decide to try floating the CT or not.

Jim
Wd5JKO

[KA2DZT]

Jim,

Good point on the line voltage.  Alan says that this xfmr has already been used in a FWB set up.  So, CT should be OK not being grounded.

Fred

[W4AMV]

Tnx Fred and Jim for additional inputs. Prior use was in a VOLTAGE DOUBLER. This xmfr used with cap input total C at 100 uF and 4000V. The tubes were a pair of 4-400A's running grounded grid. That in itself is still a bit of a mystery how well that worked. My plan(s) either a pair of 811A's or a single 813.