Radio Chassis Cradle

[Yorkie]

Yes, if it's the post-war T16/T17 AC only version they had 6.3V parallel heaters powered from an auto transformer, using an indirectly heated cathode on the rectifier valve, powered from the same 6.3V supply, rather than from a separate winding. An auto transformer is far superior to a mains dropper as it doesn't dissipate the heat that a mains dropper does, which is kinder to the cabinet and to other components, though as you say, the same precauions must be taken as an auto transformer doesn't isolate the chassis from the mains.

David, According to my Trader service sheet the Transformer is a conventional double wound isolation type transformer and on test the windings do appear to be seperate, but both primary and secondary windings are connected to earth which would negate any isolation, so just as dangerous just a little cooler. The Bakelite case also doesn't have the Asbestos heat shield built into the top, which was probably more dangerous to life than anything else ...........

Mike

A rather belated response to your comments Mike, but having looked again at the circuit I see that I was mistaken - it doesn't in fact use an auto-transformer - just a heater filament transformer, with the HT straight from the mains. An auto transformer is one in which the primary is tapped part way down so that although the HT is still taken straight from the mains (so all the same precautions as with live chassis designs are called for), as it's from a tapping on the primary the HT voltage is dropped to the required level rather than wholly relying on a dropper resistor in which the mains voltage has to be dropped to a suitable level for the HT - perhaps 100V less than the mains. Some radios use droppers which generate so much heat that it would be more accurate to describe them as 'electric fires' rather than 'radios':D

Maybe by now, you've successfully used your cradle to good effect, and have completed the restoration of your 'Major Maestro', in which case, some pics would be of interest!

MOD NOTE: Quotes tidied up.