Hallicrafters S120 hum at no vol and hum with volume

[tubetwister]

Originally Posted by old_coot88

Dude, just to reiterate, check the heater wiring to verify that the 1st audio tube's heater is at the bottom (ground) end of the string. If it's not, it could be introducing hum downstream of the vol. control

that sounds plausible and also given that the factory put in the incorrect uf value output tube control grid cap,

SRSLY no joke and it exact matches mica caps all over that radio and its a .0046 uf Mica vs an .001 presumably film cap it's supposed to have there per the schematic and the AA5 reference design that can go to .002 uf also
who knows what else they did .

I'm obviously not an AA5 or even radio expert like most of you here , so the input is all good and teaching me thank's

During my career ,some of those screw ups and product were butt of inside humor or more or a PITA ,

IOW some misplaced wires would not suprise me in a USA mid century home radio ,they already put the wrong output tube cntrl.grid cap in that crude radio with 1936 AA5 budget model ciruits in a deaf SWL 1965 radio .


It's almost criminal and that radio or a AA4/AA5 would be today because it can electrocute us without much provocation ! You cant make that up