Power Transformer ratings?

[Blair]

Hi Gregg,

Thanks for the offer, but I am always prowling for parts. I build mostly preamps and sell them to keep my hobby going. Recently, someone bought the remainder of my surplus stock of transformers online, so I am left at a new beginning:)

I rarely build amps for sale, and doubt I will ever reach the iconic level of Tom and Min, but it is fun!

Thanks again for yours and everyone's help here!

Blair

[Blair]

To revisit this thread and make sure I "get" it, I have an HT receiver transformer I would like to use for a preamp.

I measured the HV winding at 90VCT, so I measured 90V across the whole winding with a resistance of .9 ohms across the entire winding.

So, 10% of 90 is 9/.9=10

Is this a 10A winding, or do I need to divide it by 5?

There is also a 38VCT winding with a total winding resistance of .6 ohms.

3.8/.6=6.33A is this correct?

Thanks!

Blair

[Geek]

Hi,

I've only tested this rule of thumb for vacuum tube power transformers.

I doubt that it's a 90V @ 10A winding... that's 900VA and the transformer should be in the neighbourhood of 10Kg, then.

On HT amp transformers, I personally go by the wire size (the wire is usually visible) and the chart I have about 1/2 way down the page: http://geek.scorpiorising.ca/lcms/index ... ansformers

Cheers!

[EWBrown]

How big / heavy is this 90VAC transformer?

I have a PT from some "no-name" 1960's Japanese made 6MB8 integrated amp (or receiver) which has two 6.3 VAC filament windings, and one fairly hefty 90 VAC winding, this was used with a voltage doubler circuit to generate about 230-240VAC VDC under the normal B+ current load. The winding is fairly hefty, with high current, because the voltage doubler circuitry consumes about 3.6X AC current to produce a given B+ DC current.

Presuming that the B+ total current is 200 mA (which is probably about 25% more than actual DC consumption), then the 90VAC wnding's current rating would have to be at least 720 mA.

This transformer is somewhat smaller and lighter than the standard ST-70 power trannie.

/ed B

[Blair]

Hi Ed,

This is definitely bigger than an ST-70 PT it outweighs it also.



Gregg, it could be pretty beefy really because the amp was rated at 3 X 100W and 2 x 50W for 5.1. Here is an image of the windings.



It just looked like a good candidate for a doubler.

Blair

[Geek]

Ohhhh, I have one of those! yeah, it's good for about 3A in FWCT