I have a pioneer sa-410 amplifier with open circuit mains transformer (on primary). Can anyone tell me what the secondary ac output is, and the current rating. Many thanks
Only schematic I can find is the sa-610.. and that has no details of the transformer except that it is a xxx-0-xxx secondary with a fuseable link in the primary winding. Educated guess time (knowing a bit about audio amps) Have a look at the main smoothing caps. They are usually rated at twice the transformer secondary voltage.. What is the rated power output per channel RMS?.. add them together gives a figure of xxx watts.. example.. say 60.. so we can work it out by a bit of rule of thumb.. allowing for losses in the output stages and the rest of the circuitry a nice guess would be the full amp wants about 80 watts on full load.. damn.. It's been so long I can't remember how to do it My brain says to me.. and I couldn't begin to explain how or why.. 24-0-24 secondary @ 6A But as it's a mains safety component seek professional advice or you could burn the house down. Remember something caused the primary to blow the fusible link.. which says to me there is a pretty serious fault somewhere else, either in the power supply or the output stages. Seriously.. If you don't know enough about electronics to look at the other components in the power supply and make an educated guess on the rating.. should you really be trying to fix it? The transformer will output the same in AC as the output DC from the bridge rectifier.. and that is usually printed on the top (or google it by number) or printed on the board somewhere. TP 24v or something similar.
Assuming that the mains winding has failed open circuit the most effective way of determining the winding voltages of your transformer is as follows: 1/ Disconnect all transformer connections or make sure all valves and any other loads are removed from the amplifier. 2/ Be aware that during this process high voltages will appear on some secondaries. 3/ Locate a heater winding (there may be more than one), This will be the one with the thickest copper wires. 4/ Obtain a 6.3 volt a.c. supply (switched off) and connect it to the heater winding. (Another valve amp transformer could be used for this). 5/ After making sure that any flying wires are safe and seperated and preferably secured into a nylon connector block you can now switch on the 6.3 volt supply. 6/ Accurate measurement with a suitable D.V.M. that measures R.M.S. can now be made of all other windings with the exception of course of the mains winding which you don't need to know anyway. REMEMBER !!! Please be careful, you could have around 900V total across the centre tapped H.T winding (450-0-450) - this could be lethal. Happy fault finding --- Tony D
