# Transformer substitution help

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#### moray james

I just asked Hammond for a step up transformer to run a HV ESL supply. I need 120V in and 750V out almost no current necessary. Quote was about \$285.00 OUCH!!!
Can anybody suggest a transformer running backwards that would work for a lot less money? Thanks for the help/suggestions. Regards Moray James

#### gingertube

Just a suggestion - You might try 269GX.

These are 225 - 0 - 225 transformers with 6.3V 2.5A Heater supplies which you probably don't need.

Leave the centre tap not connected and feed the full secondary i.e. the 225 and 225 (450V total) taps to a voltage doubler. This will probably give you around 1050 to 1100 volt rail.

If thats too much then I think there are 200 - 0 - 200 Volt (to give about 950 to 1000 volt) and even 180 - 0 - 180 (to give about 850 to 900 volt rail) trannies in the standard range

Because you are using the full secondary on both half cycles rather than half at a time on each half cycle you want to get a transformer rated for twice the current you are actually going to draw.

Rail volts above calculated on 2.4 times the rated voltage (i.e. 225 + 225 = 450 x 2.4 = 1080 volts) . If you are actually drawing practically no current, then you will get more than this - approx 2.8 times rated voltage which in this case would be 1260 volts.

you might want to model it using PSUD II from the Duncan Amps site before choosing the tranny.

Cheers,
Ian

#### moray james

This transformer feeds a cap/diode multiplier that outputs 5KV that feeds a 500 meg ohm resistor then on to the diaphragm. Hope this explains better the job at hand. I know squat about transformers so your help is most welcome. Regards Moray James.

#### PRR

Paid Member
> I need 120V in and 750V out

From context, this is 750VAC.

Use something like 375-0-375VAC, and just take the two Red end wires, tape-off the Red/Yel, Violet, and other un-used wires. Since transformers are rated full-load and your load is near-zero, but not too tolerant of overvoltage, go for about 325-0-325 or 350-0-350. Which in Hammond's standard 300 line looks like this:

372X 75 310-0-310 70 50 5V CT @ 2A 6.3V CT @ 2.4A - X8
376X 157 320-0-320 150 50 5V CT @ 3A 6.3V CT @ 5A - X20
373AZ 52 325-0-325 40 50 5V CT @ 2A 6.3V CT @ 2A - Z6
373CZ 159 325-0-325 150 50 5V CT @ 3A 6.3V CT @ 5A - X20
373DX 101 350-0-350 90 50 5V CT @ 2A 6.3V CT @ 3A - X10
373DZ 101 350-0-350 90 50 5V CT @ 2A 6.3V CT @ 3A - Z10
373X 125 350-0-350 110 50 5V CT @ 2A 6.3V CT @ 4A - X11
373BX 187 350-0-350 175 50 5V CT @ 3A 6.3V CT @ 5A - X13
374AX 136 360-0-360 120 50 5V CT @ 3A 6.3V CT @ 3.5A - X11

Lower "X" numbers are physically smaller, and probably cheaper. Nobody actually stocks all parts; I leave it to you to find the best deal.

#### moray james

Many thanks

I will check availability and cost of these at the local dealer tomorrow. Thanks for the help and information. Regards Moray James.

#### Tom Bavis

If one side of this supply is grounded, no problem. Transformer insulation could be a problem otherwise. Actually, Hammond doesn't recommend using the center-tapped transformers this way, but they are 100% tested at high voltage, typically 2*V +1000 Volts.

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