15-07-2013, 07:00 PM
(14-07-2013, 07:00 PM)pwdrive Wrote: I think those larger sized dogbones are around 2 Watts or so? they did some big fat ones as well, about 12 mm in diameter, my old Marconi CR300 has one of them in the heater circuit I seem to recollect, I guess those ones are nearer 5 Watt.
Lawrence.
Just checked in the CR300 book of words, the large dogbone is 120 ohms but no wattage rating is given.
However the CR300 uses a 24-28 volt heater supply, (from a seperate power supply) the valves are .3 amp heaters except the sound output valve (6V6G) it's heaters are .45 amp, that valve is in series with two KTW61's and a DH63 so that means the last mentioned valves need the 120 ohm resistor across them to give a current of .45 amp to match the current of the 6V6G heaters, this means the dogbone needs to be able to dissipate 2.7 watts, so as a guess I would say it is rated somewhere between 3 and 5 watts.
Just to avoid any confusion the total number of valves in the receiver are arranged in a twin series parallel arrangement ie: four 6.3v heater valves in each series circuit the two series circuits then being connected in parallel.
Lawrence.
