[Amps] Limits of a Power transformer

[Steve Thompson]

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. If I full wave rectify it I
> should get a noload voltage of about 2.6Kv. I have 9 470uf 450V
> 105degree CDE electrolytic caps. Maybe I don't have to use all of them?
> With the secondary being 160 ohms will I need step start circuitry to
> limit the inrush current to the capacitors?
> 	My mode of operation is going to be SSB. How much power could I
> squeeze out of this transformer. I am going to design this to be a
> class-B amp. My bias point is going to be at the tube cutoff voltage.
> Looking at the PDF file available online it looks to be -45v. It will be
> a GG design with tuned input.
There's a useful tool at http://www.duncanamps.com/psud2/index.html

Plug in your values and get predictions of what your PSU will do in 
practice (accurate predictions in my experience). Run with zero delay to 
see the input surge (10Aish at 240V) and 1s delay to see the settled 
operating conditions with different loads. Look at the RMS currents in 
the caps to compare against their ripple ratings and RMS current in the 
transformer to see the heating effect in it.

Personally, I'd use all the capacitors, just to get the final value down 
and reduce the stored energy.

Steve