Putting this into "repair" though it is really "modification".
I have a Parasound HCA-1200 amplifier from the 1990s. I bought it in the USA but now live in Germany. The amp is set up for 120V 50/60Hz, and I have used it in the past with a 240V/120V transformer. I'd like to eliminate that conversion transformer and if possible power it directly from the mains.
While the amplifier has no provision to switch input voltages, I just took a look at the large (1kVA) torroidal transformer that provides DC. The good news: the primary comes out as four wires, with two pairs in parallel. So I think it is likely that there are two primary coils, currently being run in parallel, and that if I put them into series then I can drive the transformer directly from 230V.
The amplifier has a soft-start circuit. When initially turned on, there is a 10 ohm 30W resistor in series with the primary. Then, when the DC voltage (from a separate low-current secondary winding, time constant set by a 22uF capacitor and a 220k resistor, so a couple of seconds) has risen to a reasonable level a relay closes and shorts out the 10 ohm resistor. I assume this is to keep the input surge current down and also to provide a gentler start to the amplifier itself.
My question: if I am correct that if there are two primary windings, currently in parallel, and that all I need to do is put them in series, then is it also correct that I should replace the 10 ohm 30W resistor with a 20 ohm 30W resistor, to maintain the soft start? (If so, I will probably get another 10 ohm 30W resistor and put it in series, thus ending up with a 20 ohm 60W resistor.)
Snapshot of the relevant bit of the schematic is attached. The resistor in question is R05. Note that this schematic does not show the primary as made of two separate windings.
Thanks, Bruce