backwards transformers

[Positron]

Yes, Chris, refreshed my memory back to the good old college days, when every part was worth its weight in gold. Searched and saved every part I could find to be reused again.

[tiroth]

theChris,

I don't know how much current or what voltage you need. But I would consider getting two of Steve's smaller transformers unless the Basler is just what you need. I mean, you could get a couple of the $4 ones and still have some cash left over. You could even use three if you need more voltage.

Steve has had tubes on stock in the past, so you could do some one-stop-shopping. I suggest you ask him what he's got because I've been surprised in the past at the things that don't make it onto the site.

[PRR]

> "instantly" because I wanted to scare him

"Instant death" may be possible. I don't want him disappointed if he has to wait a minute for flames (or just stinky smoke) to pour out.

Chris, what do you really want? Tube headphone amp? How can you need a 300 watt transformer?

You want fairly high power at 6 or 12 volts (heaters), and probably not-much power at 250-350VDC for the plates.

A 115/230:12V 48VA transformer is a universal item selling for $12 or so. Two of these plus a resistor-pack will make a minimum order most places.

Wire one transformer for your local line voltage (120V or 230V... Illinois is in 120V-land). Wire the 12V winding of the first tranny into the 12V winding of the second tranny. The other side will give 115/230VAC, and the 230VAC winding will give about 330VDC after rectification, enough to run most tubes.

The 12V winding also powers your heaters. Run 6V tubes in series to make a 12V string. Or rectify to DC and do your math.

A pair of 48VA cores working this way will supply 12V-2A of heaters (an awful lot of mini-9-pins) and about 50mA of plate power before the double-core configuration sags the voltage enough to be a problem.

> parts i ...could reuse if the amp ever got take out of use.

A 12V 48VA tranny is always useful. Put a car tail-light bulb on it for a compact powerful light-source. Use a 2-diode voltage doubler to make +/-17V to power scores of op-amp chips (whoops, wrong forum). Heater power for your next quad-6550 150Watt speaker-amp project. Even works as a doorbell transformer (though permanently install bell transformers are supposed to have flame-proofing and electrician-type connections).

[theChris]

what happens to current output rating when you do this. like if you had 2 50V (1A) transformers and hooked them up with secondaries in series, you would get 100V (1A) right? or is there de-rating? i assume the output impedance of the tranformer combo will increase, but anything else?

[PassFan]

Originally posted by theChris
what happens to current output rating when you do this. like if you had 2 50V (1A) transformers and hooked them up with secondaries in series, you would get 100V (1A) right? or is there de-rating? i assume the output impedance of the tranformer combo will increase, but anything else?

In a series circuit voltage adds and current remains the same. In a parallel circuit current adds and voltage remains the same. In a sense though your VA's will increase, 50 volts x 1 amp = 50 VA's. 100 volts x 1 amp = 100 VA's. So you doubled the wattage or VA's your secondary would deliver. Wattage and VA's are basically the same thing.