hallicrafters tw-500

[pwdrive]

hi joe and guys, the schematic that colin kindly sent me , gives.... il6. iu4, iu4, iu5. 3v4, my set is fitted with dk96 ,df 86, df86,daf91, and a brimar [unknown] four of the d type are mullard ,the numbering is anything but clear , so the plot thickens, any suggestions chaps ?maitiu.

The 96 series are 25ma heater current, the 91 is 50ma heater current, if they are all still connected in series then the heater shunt values need to be adjusted to compensate, don't forget that the shunts will also shunt the anode/screen currents.
Personally I would investigate all the heater shunt resistors to see if they are the original specified values or if they have been changed at some time for different values, then take it from there. Let the forum know if they are the original values as specified in the schematic.

Lawrence

Forgot to add that if by any chance the output valve has 50ma heaters then that along with the DAF91 which is also 50ma will put a serious strain on the other 96 series valves which are 25ma heaters if the latter heaters haven't been sufficiently shunted, I would also check the heater feed dropper resistor as well which is switched in on mains operation.
It would be handy to draw a schematic diagram of the whole heater chain as it stands so you can see what's exactly what.

Lawrence.