Re: [Amps] Tuned power transformer

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

Angel Vilaseca wrote:
> I am taking apart an old HV power supply made in the late '40s, 
> probably in Germany. From its size, the power transformer should be 
> rated for approximately 1 KW. It has an HV secondary winding 800-0-800 
> Volts and two 12 V for filaments. It has a vacuum rectifier.
>
> It has tuned chokes and I also found that a 10 uF cap is wired across 
> the primary winding of the power transformer.
>
> So I guess that this must be a tuned-primary power trnsformer. I never 
> saw this before. How does this work? What are the properties of a 
> tuned-primary power transformer? Does it prevent current inrush at 
> power-on like a tuned choke?
>
> Of course, I will replace the vacuum rectifier with solid-state diodes. 
> Should I leave the 10 uF cap acros ethe primary or remove it?

The capacitor is probably for power factor correction.

There are a number of unusual things about this power supply, so you 
should be a little bit suspicious about the transformer.

If you can, try to see if the core configuration looks normal - look 
particularly for any deliberate gaps or magnetic shunts. Measure the 
primary and secondary DC resistances to check if those appear normal 
too, as compared with similar transformers - a few tens of ohms for the 
secondary; a few ohms maximum for the primary.

If you intend to use the whole secondary with a full-wave bridge and 
capacitor input (should give about 2kV on load), test the transformer 
with an existing power supply before you build it into a new one.


--
73 from Ian G3SEK
http://www.ifwtech.co.uk/g3sek
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