Muirhead B-21-F Decade Condenser Internally screened polished wood case with polished black front panel. Three decade switches; tenths, hundredths and thousandths microfarad. UK
The Muirhead decade condensers were I believe made at their Elmers End works a mile or two from where I live, the factory has now gone to be replaced by a Tesco supermarket. No I do not know what would be the safe max voltage you could put across it, but I guess the typical 250v or so would not do it any harm. Mine was open circuit on many of the settings, this was because the contacts which as I remember were silver plated had gone very black. After cleaning all was well and I used it to check my Mullard CR bridge.
