51-0-51 Toroidal transformer and virtual ground

[ondreji]

I salvaged this beast from audio amp. My original plan was to "upgrade" my linear PSU but then I realised that make use of 51V is quite difficult. There is an another 18-0-18 winding as well (but that would be no difference to what I have now apart from the fact that PSU will double the weight)

The best idea so far is to use opa548 (5A) or lm675 (3A) to create virtual ground. I did some reasearch:

http://www.goldpt.com/virtual_ground_circuit.html
http://www.radiolocman.com/shem/schematics.html?di=150753
http://forum.allaboutcircuits.com/threads/creating-a-virtual-power-supply-article.13678/
http://forum.allaboutcircuits.com/threads/plus-and-minus-9v-from-one-9v-battery.12989/#post-79413
http://tangentsoft.net/elec/vgrounds.html
http://www.jamesclements.net/heres-a-rail-splitter-circuit-30v-in-15v-out-aka-virtual-ground/

at the end of day it seems to be cheaper to just buy appropriately sized transformer. But then I'm not going to learn anything new 

Any suggestion?

[amspire]

Do you know the currents of the windings? My guess is that the 51V will be several amps at least, but the 18-0-18 could be only 1/2 an amp.

For a linear power supply, it would be better to have more taps in the 51-0-51 windings unless you want to make a high voltage supply at a limited amperage - like 0-120V at 1 A.

[ondreji]

Amperage is not marked but I was able to get almost 400W without getting it too hot (over 30min). Based on the weight it might be between 400 - 600VA.

I would say that 51-0-51 is close to 4A and 18-0-18 might be up to 2A. Multiple taps would be ideal but I haven't seen transformers like that (readily on the market).

Virtual ground allows me to have up to "8A". 10A op-amps are ridiculously expensive. So far the options are:
- multiple opa548 (two or three)
- multiple lm675 (five?)
- lt1970 + external FETs, low current PSU for LT1970, ...

[ondreji]

This turned out to be a great waste of time. Op-amp would need to dissipate around 80W (P = I*(Vrail - Vout) = 3A*(50-25)).

This is too much even for op-amp like PA50 (100A peak, 40A, ~$850). The SOA chat for 25V difference (rail - output) allows up to 4A only.

Another paperweight... (that toroidal transformer)