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Hi folks, I just wanted to ask how safe is it to run a transformer in reverse? I'm currently looking at one rated at 250va with 0-115 0-115 secondary and multiple primary inputs from 230-700 volts. The amp I want to build requires an ht of 700v to run 4 kt88. So I'm thinking of running it in reverse and using the 500 volt tap as the ht supply. Has anyone done this, is it safe?
Thanks for reading
Cheers Just

I've done it. Was told to degrade performance about 15%, and it might lose a bit or regulation.
What I do to check transfomers is to series string together several light bulbs, all the same power and get them to the current that the transformer is rated for and make sure it doesn't get too hot. Give it at least 2 hours.

DeathRex wrote:Was told to degrade performance about 15%, and it might lose a bit or regulation.

This is accurate.

Transformers normally can be run like this, unless their datasheet specifically specifies they do not (some Signal, Tamura and Triad do, as their energy-limiting cores will saturate quickly).

Cheers!

Newbietube wrote:Hi folks, I just wanted to ask how safe is it to run a transformer in reverse? I'm currently looking at one rated at 250va with 0-115 0-115 secondary and multiple primary inputs from 230-700 volts. The amp I want to build requires an ht of 700v to run 4 kt88. So I'm thinking of running it in reverse and using the 500 volt tap as the ht supply. Has anyone done this, is it safe?
Thanks for reading
Cheers Just

It doesn't matter: it's a bilateral device. Just make sure you don't make a wiring mistake such as putting 230V across parallel connected 115V coils instead of series connecting them, and do make sure the series connected coils are phased correctly, or letting unused taps cross, to prevent poofage.

From the description, this looks like a "control transformer". Its 250VA rating presumes an AC load, so don't be expecting to extract 250W of DC power from it, as you'll have to de-rate to use it in a bulk DC power supply.

Thanks folks, pretty much answers my question.