Which mounting box ? (there's a 10.5" one (BA11-K IIRC) where the PCBs go in from the top with a PSU on the back or a 21" one (BA11-F ?) where the PCBs go in from the left side and with a separate H742 PSU in the rack). Do you have any periperhals for them? THere are 2 main issues. Voltage and Frequency. AFAIK the PSUS in these mahcines all have trnasofomres with 2 primary windings which are wired in series for 230V and parallel for 115V. The fans are 115V and run off the trnasformer primary (acting as an autotransformer)_ for 230V mains. There may also be a small transformer as part of the power control circuitry. Looking at hte printset nad compairing the wiring for 115V or 230V mains shold tell you what to do. I can take a look if you let me know eaactly what you have. The differnece in mains frequency is not an issue for the CPU unit. Some peripehrals most certianly care abvout it (the RK05 disk, for exmaple, the disk speed is set my the mains frequency, so there's a pulley change if you go between 50Hz and 60Hz). There is a 'line time clock' (I think it's an option in the 11/35, but most have it). This generates an interrupt every (half?-) cycle of the mains. Most OSes have a configuration option for 50Hz mains, there's no hardware change. That sort of trnasofmrer is very useful!. However, there is an electrical differeice between its output and normal US mains, namely that US mains has one side (neutraL) connected to safety grounmd, these trnasofmers have the centre tap of the secondary connected to groud. This is not an issue with PDP11s, though. THey will run fine from such a trnasformer (I've done it for testing). I suspect you can rewire the PSU, You will not have to replace the large transoformer or the fans, you might have to replace the little trnasofrmrer for the power control. -tony

On 07/10/2011 12:52, Tobias Russell wrote: It's safe, but not very efficient, and there a few other considerations. First, you need to realise that a lot of those big yellow site transformers are not rated for continuous use at the load they claim. They're intended to run power tools which by their nature are used intermittently. I don't know about that particular one, but most need derated by 50%-75% for continuous operation.

Secondly, they produce 55-0-55VAC, ie centre-tapped to ground. Probably not an issue, but you should be aware of it. Lastly, although transformers can be very efficient, no transformer is 100% efficient (80%-90% is more typical).

The 11/35 (ditto the 11/40, like mine) uses an H742 supply to drive the

power bricks. It has a terminal strip inside that you can easily jumper for either 110V or 230V, so there's no reason not to just change it. Well, no reason except the damned thing is VERY heavy and therfoe awkward to handle, but you already know that :-)