[Amps] Limits of a Power transformer

[Ian White GM3SEK]

Tom W8JI wrote:
>> Nat Gurumoorthy wrote:
>>> Hi,
>>> I am in the process of scrounging together parts for a
>>> linear
>>> amp. I have a pair of GI-7BT. I have acquired a Triad
>>> P-14A (115
>>> primary, 1780V 250ma CCS secondary) Weighs about 14lbs.
>>> Secondary
>>> resistance seems to be about 160 ohms.
>
>I think you'll find a 160 ohm ESR transformer has horrible
>regulation.
>
>The hypersil in the AL12 series for example has about 10
>ohms of secondary resistance. The AL-811 around 20 ohms ESR.
>
>With 160 ohms secondary resistance the value of capacitance
>does not matter nearly as much, so I'd not worry about
>having higher values of C. As Steve points out, all it does
>is complicate stored energy problems.
>
>I'd look at that transformer real close before using it.
>Odds are it was never designed for capacitor input solid
>state supplies.

Don't forget the effect of primary resistance. It may seem low (often so 
low that it's difficult to measure accurately) but the value has to be 
multiplied by (turns ratio)-squared, and then added to the secondary 
resistance.

The total is the "effective Rs" value that you need to use in all 
calculations of voltage regulation. Unless the primary winding has been 
generously over-sized, the total effective Rs is often about 2x the 
secondary resistance alone.



-- 
73 from Ian GM3SEK