HV transformer applicability

[k7mdo]

I "acquired" a power transformer at the local surplus house and am wondering about its potential as a "universal" transformer for a HV bench supply.

I often get HF projects going with tubes and they always need plate, filament and/screen supplies.  My hope with this transformer was that maybe I would just have a single supply that I could use to test the projects rather than always building a supply for each one and later finding out that my project requires some tweaking of its power supply before I finalize it by building a dedicated one for it. 

My only real concern is that the transformer has what I would think is an odd set of primaries.  It has four (4) 110 vac with only a single secondary. 

Does anyone feel this presents a problem and/or whould I parallel up the primaries or just use two  and then use the other two for additional HV secondary voltages?

Ideas? 73, Tom

4X110 VAC primaries
0/373/545/803 VAC secondary @ .735 ampere

[N2DTS]

That is some odd iron.
I suppose you can paralel the 110 windings, but its not center tapped on the secondary, which means bridge which is not my favorite way to build a supply.

My big supplies are all generic, step start, variac, choke input, oil filled cap output, 0 to 3000 volts.

Last winter I built a VFO-exciter for my 2x 4x125 rig, and only having two small chassis, I put the power supply on its on chassis.
Its got a wire wound pot unregulated voltage output for the screen supply, a regulated (VR tubes) supply fed with another wire wound so I can plug in various VR tubes to get the regulated voltage I want, and a seperate HV output (600 volts I think).

It makes a lot of sense to build things in a modular way, and make things adjustable.

I have a rack that takes two RF decks, power supply, modulator, control deck, vfo/exciter, rf deck.
I could build yet another RF deck, or modulator, and just plug it in, or mix and match any deck to any other.

[w4bfs]

this is basically a 600W xfmr and if you use it step-up then there will need some idea of the 110V winding size.... Ohm it out and see if the 110V windings ohm out similarly .... probably just a few ohms with a 10 or so max

[W3RSW]

Good idea to ohm It out.
Primaries probably identical. Industrial, with options to run 110/220/440 back in the day.

Not sure the "0" tap on secondary can handle the full AC to case if used as a bridge full wave rectifier.  One way to find out.

I like the idea of using some of the primaries as auxiliaries for other DC supplies. Of course the main secondary will have to be derated, not just for what's pulled by the aux. windings but by the loss of how many other primary feeds are used for other purposes.

[KA2DZT]

I agree with Rick,  110/220/440 volt primary, industrial xfmr.  To get the full current load from the secondary you need to used all the primary windings.  Four in parallel for 110 volts, two parallel pairs in series for 220 volts.  Using some of the primaries in series with the secondary made exceed the wkg voltage rating of the primary.

A better way the increase the output voltage is to do the following;

Use a FWB rectifier on the secondary.  This will yield about 800VDC.  Use two of the 110 primary windings in series, put another FWB rectifier across those two windings.  This will yield about another 220 VDC.  Now use the 220V FWB rectifier output (from the diodes) and connect it directly to the negative terminal of the FWB rectifier diodes of the secondary(note that the 800V diode negative is not grounded)(the diode negative of the 220 FWB is grounded).  The two voltages will add together giving you about 1000 volts.  With the higher AC line voltage (120-125 volts) you should get better than 1100 volts into your filter.  The filter output will be less with choke input, higher with cap input.  You have to reduce the current load to half the rated current because you are only using two of the primary windings for your primary side.  Using this method you will notice that you haven't exceeded any of the voltage ratings of the xfmr.

This method will also work with any two separate xfmrs.  Using two separate xfmrs the second xfmr in the series has to have a high enough voltage rating on its secondary winding.  Note your xfmr has a 2100 volts wkg rating.

Using two xfmrs, you can reduce the output voltage by simple shutting off either xfmr.  No need the alter any connections, simple shut off either xfmr.

This will give you ideas to work on.  Especially if you have any additional xfmrs to work with.

Fred

[k7mdo]

For those that asked about "ohming" the 4 110vac windings..  here it is: (caveat: used Fluke model 77)

1-2: 1.2 ohms
3-4: 1.35 ohms
5-6: 1.45 ohms
7-8: 1.5 ohms

I would bet 1-2 and 3-4 are the same and 5-6 and 7-8 are the same within the statistical boundaries of the number of measurements taken.

This is certainly at the low end of the Fluke's capability but on repeated mearurments I got fairly consistent readings.  To eliminate some of the issues with such low readings I "randomly" took them, not in sequence.  I have found the Fluke to have some hysteresis(?) in sequential measurements.

On another note, I am not sure I need more than 3 or 4 different hv voltages from this unit, particularly if I make limited and conservative use of a variac on the primary side.

There should be plenty of arrangements for a range of outputs that would satisfy my future requirements. I hope.

Thanks for the input, Tom

[KA2DZT]

For those that asked about "ohming" the 4 110vac windings..  here it is: (caveat: used Fluke model 77)

1-2: 1.2 ohms
3-4: 1.35 ohms
5-6: 1.45 ohms
7-8: 1.5 ohms

I would bet 1-2 and 3-4 are the same and 5-6 and 7-8 are the same within the statistical boundaries of the number of measurements taken.

This is certainly at the low end of the Fluke's capability but on repeated mearurments I got fairly consistent readings.  To eliminate some of the issues with such low readings I "randomly" took them, not in sequence.  I have found the Fluke to have some hysteresis(?) in sequential measurements.

On another note, I am not sure I need more than 3 or 4 different hv voltages from this unit, particularly if I make limited and conservative use of a variac on the primary side.

There should be plenty of arrangements for a range of outputs that would satisfy my future requirements. I hope.

Thanks for the input, Tom

Those resistances make perfect sense.  Each one is slightly higher than the last.  Each winding is wound over the last requiring a greater length of copper wire to complete the same number of turns, thus a slightly greater resistance.  No need to worry about any of those primary measurements.  Primary windings usually have very low resistances.

Fred

[wa3dsp]

It looks like it was intended to be used as a  110V/220V/440v  primary in different series/parallel arrangements. The primary windings have a 690V rating so I wouldn't mix them with the secondary.

It would give you possibly a good solid 850 volts with a bridge and a choke input. The primary is 110V so with typically 120V it would run 10% higher on secondary voltages. It would be great for a sweep tube amplifier supply back when you could get tubes. It would do 1000 watts icas in SSB service I am sure. Maybe a half dozen 6146's in parallel!!

You could also use a voltage doubler and have enough voltage for an 813 or 811/572.

With a variac it would make a good 0-800 volt bench supply

[W3RSW]

4d32 Heaven.
Pair or trio modulated by a pair.  Choke input supply and just watch the screen voltage.  Even Art Collins thought ICAS wasn't enough to push these babies.  _{no reference, just Puttin' words in his mouth.}

Also see n2dts's remarks in some posts.

I don't think I've ever heard of a 4d32 going south.  Similar to 813's, a way underrated tube.